1
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Xu W, Yao Y, Zhu D, Han L, Wang L, Wang Y. Involvement of the BNP/NPR-A/BKCa pathway in rat trigeminal ganglia following chronic constriction injury. J Neurophysiol 2021; 125:1139-1145. [PMID: 33596737 DOI: 10.1152/jn.00682.2020] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Accumulating evidence indicates that the brain natriuretic peptide (BNP) and its receptor (natriuretic peptide receptor, NPR) are widely distributed in a variety of tissues including trigeminal ganglion (TG). Furthermore, recent studies support the involvement of the BNP-NPR-A pathway in acute and chronic pain. To investigate the role of this pathway in chronic pain, an infraorbital nerve-chronic constriction injury (ION-CCI) model of trigeminal neuralgia (TN) was produced in the rat. The time course of changes in mechanical pain threshold was examined. We observed an upregulation of BNP and NPR-A and a downregulation of large-conductance Ca2+-activated K+ (BKCa) mRNA and protein in rats subjected to ION-CCI. Patch clamping experiments in vitro found that BKCa currents were significantly reduced in rats subjected to ION-CCI. BNP increased BKCa currents in ION-CCI rats. These results suggest that BNP and NPR-A might serve as endogenous pain relievers in ION-CCI rats. Modulation of the BNP/NPR-A/BKCa channel pathway in TG may be a viable strategy for the treatment of TN.NEW & NOTEWORTHY BNP has been known to activate its receptor, NPR-A, to modulate inflammatory pain. However, the potential modulatory roles of BNP in TN have not been investigated in detail. We established an ION-CCI model of TN in the rat and observed an upregulation of BNP and NPR-A and a downregulation of BKCa in rats subjected to ION-CCI. Moreover, BNP can increase BKCa currents in ION-CCI rats. Thus, BNP and NPR-A might have inhibitory effects on trigeminal neuralgia through activating the BNP/NPR-A/BKCa channel pathway.
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Affiliation(s)
- Wenhua Xu
- Key Lab of Oral Diseases Research of Anhui Province, Stomatologic Hospital & College, Anhui Medical University, Hefei, People's Republic of China
| | - Yuzhi Yao
- Key Lab of Oral Diseases Research of Anhui Province, Stomatologic Hospital & College, Anhui Medical University, Hefei, People's Republic of China
| | - Dawei Zhu
- Key Lab of Oral Diseases Research of Anhui Province, Stomatologic Hospital & College, Anhui Medical University, Hefei, People's Republic of China
| | - Liang Han
- Key Lab of Oral Diseases Research of Anhui Province, Stomatologic Hospital & College, Anhui Medical University, Hefei, People's Republic of China
| | - Liecheng Wang
- Department of Physiology, School of Basic Medical Sciences, Anhui Medical University, Hefei, People's Republic of China
| | - Yuanyin Wang
- Key Lab of Oral Diseases Research of Anhui Province, Stomatologic Hospital & College, Anhui Medical University, Hefei, People's Republic of China
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2
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Babicheva A, Ayon RJ, Zhao T, Ek Vitorin JF, Pohl NM, Yamamura A, Yamamura H, Quinton BA, Ba M, Wu L, Ravellette KS, Rahimi S, Balistrieri F, Harrington A, Vanderpool RR, Thistlethwaite PA, Makino A, Yuan JXJ. MicroRNA-mediated downregulation of K + channels in pulmonary arterial hypertension. Am J Physiol Lung Cell Mol Physiol 2020; 318:L10-L26. [PMID: 31553627 PMCID: PMC6985878 DOI: 10.1152/ajplung.00010.2019] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2019] [Revised: 08/19/2019] [Accepted: 09/06/2019] [Indexed: 12/22/2022] Open
Abstract
Downregulated expression of K+ channels and decreased K+ currents in pulmonary artery smooth muscle cells (PASMC) have been implicated in the development of sustained pulmonary vasoconstriction and vascular remodeling in patients with idiopathic pulmonary arterial hypertension (IPAH). However, it is unclear exactly how K+ channels are downregulated in IPAH-PASMC. MicroRNAs (miRNAs) are small non-coding RNAs that are capable of posttranscriptionally regulating gene expression by binding to the 3'-untranslated regions of their targeted mRNAs. Here, we report that specific miRNAs are responsible for the decreased K+ channel expression and function in IPAH-PASMC. We identified 3 miRNAs (miR-29b, miR-138, and miR-222) that were highly expressed in IPAH-PASMC in comparison to normal PASMC (>2.5-fold difference). Selectively upregulated miRNAs are correlated with the decreased expression and attenuated activity of K+ channels. Overexpression of miR-29b, miR-138, or miR-222 in normal PASMC significantly decreased whole cell K+ currents and downregulated voltage-gated K+ channel 1.5 (KV1.5/KCNA5) in normal PASMC. Inhibition of miR-29b in IPAH-PASMC completely recovered K+ channel function and KV1.5 expression, while miR-138 and miR-222 had a partial or no effect. Luciferase assays further revealed that KV1.5 is a direct target of miR-29b. Additionally, overexpression of miR-29b in normal PASMC decreased large-conductance Ca2+-activated K+ (BKCa) channel currents and downregulated BKCa channel β1 subunit (BKCaβ1 or KCNMB1) expression, while inhibition of miR-29b in IPAH-PASMC increased BKCa channel activity and BKCaβ1 levels. These data indicate upregulated miR-29b contributes at least partially to the attenuated function and expression of KV and BKCa channels in PASMC from patients with IPAH.
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Affiliation(s)
- Aleksandra Babicheva
- Section of Physiology, Division of Pulmonary, Critical Care and Sleep Medicine, University of California, San Diego, La Jolla, California
- Departments of Medicine and Physiology, The University of Arizona, Tucson, Arizona
| | - Ramon J Ayon
- Departments of Medicine and Physiology, The University of Arizona, Tucson, Arizona
| | - Tengteng Zhao
- Section of Physiology, Division of Pulmonary, Critical Care and Sleep Medicine, University of California, San Diego, La Jolla, California
- Departments of Medicine and Physiology, The University of Arizona, Tucson, Arizona
| | - Jose F Ek Vitorin
- Departments of Medicine and Physiology, The University of Arizona, Tucson, Arizona
| | - Nicole M Pohl
- Department of Medicine, University of Illinois at Chicago, Chicago, Illinois
| | - Aya Yamamura
- Kinjo Gakuin University School of Pharmacy, Nagoya, Japan
| | - Hisao Yamamura
- Nagoya City University Graduate School of Pharmaceutical Sciences, Nagoya, Japan
| | - Brooke A Quinton
- Departments of Medicine and Physiology, The University of Arizona, Tucson, Arizona
| | - Manqing Ba
- Departments of Medicine and Physiology, The University of Arizona, Tucson, Arizona
| | - Linda Wu
- Departments of Medicine and Physiology, The University of Arizona, Tucson, Arizona
| | - Keeley S Ravellette
- Departments of Medicine and Physiology, The University of Arizona, Tucson, Arizona
| | - Shamin Rahimi
- Section of Physiology, Division of Pulmonary, Critical Care and Sleep Medicine, University of California, San Diego, La Jolla, California
| | - Francesca Balistrieri
- Section of Physiology, Division of Pulmonary, Critical Care and Sleep Medicine, University of California, San Diego, La Jolla, California
| | - Angela Harrington
- Section of Physiology, Division of Pulmonary, Critical Care and Sleep Medicine, University of California, San Diego, La Jolla, California
| | - Rebecca R Vanderpool
- Departments of Medicine and Physiology, The University of Arizona, Tucson, Arizona
| | | | - Ayako Makino
- Division of Endocrinology and Metabolism, Department of Medicine, University of California, San Diego, La Jolla, California
- Departments of Medicine and Physiology, The University of Arizona, Tucson, Arizona
| | - Jason X-J Yuan
- Section of Physiology, Division of Pulmonary, Critical Care and Sleep Medicine, University of California, San Diego, La Jolla, California
- Departments of Medicine and Physiology, The University of Arizona, Tucson, Arizona
- Department of Medicine, University of Illinois at Chicago, Chicago, Illinois
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3
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Granados ST, Castillo K, Bravo-Moraga F, Sepúlveda RV, Carrasquel-Ursulaez W, Rojas M, Carmona E, Lorenzo-Ceballos Y, González-Nilo F, González C, Latorre R, Torres YP. The molecular nature of the 17β-Estradiol binding site in the voltage- and Ca 2+-activated K + (BK) channel β1 subunit. Sci Rep 2019; 9:9965. [PMID: 31292456 PMCID: PMC6620312 DOI: 10.1038/s41598-019-45942-1] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2019] [Accepted: 06/17/2019] [Indexed: 01/14/2023] Open
Abstract
The accessory β1 subunit modulates the Ca2+- and voltage-activated K+ (BK) channel gating properties mainly by increasing its apparent Ca2+ sensitivity. β1 plays an important role in the modulation of arterial tone and blood pressure by vascular smooth muscle cells (SMCs). 17β-estradiol (E2) increases the BK channel open probability (Po) in SMCs, through a β1 subunit-dependent modulatory effect. Here, using molecular modeling, bioinformatics, mutagenesis, and electrophysiology, we identify a cluster of hydrophobic residues in the second transmembrane domain of the β1 subunit, including the residues W163 and F166, as the binding site for E2. We further show that the increase in Po induced by E2 is associated with a stabilization of the voltage sensor in its active configuration and an increase in the coupling between the voltage sensor activation and pore opening. Since β1 is a key molecular player in vasoregulation, the findings reported here are of importance in the design of novel drugs able to modulate BK channels.
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Affiliation(s)
- Sara T Granados
- Departamento de Nutrición y Bioquímica, Facultad de Ciencias, Pontificia Universidad Javeriana, Bogotá, Colombia
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile
| | - Karen Castillo
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile
| | - Felipe Bravo-Moraga
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile
- Center for Bioinformatics and Integrative Biology, Facultad de Ciencias de la Vida, Universidad Andrés, Bello, Chile
| | - Romina V Sepúlveda
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile
- Center for Bioinformatics and Integrative Biology, Facultad de Ciencias de la Vida, Universidad Andrés, Bello, Chile
| | - Willy Carrasquel-Ursulaez
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile
| | - Maximiliano Rojas
- Center for Bioinformatics and Integrative Biology, Facultad de Ciencias de la Vida, Universidad Andrés, Bello, Chile
| | - Emerson Carmona
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile
| | - Yenisleidy Lorenzo-Ceballos
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile
| | - Fernando González-Nilo
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile
- Center for Bioinformatics and Integrative Biology, Facultad de Ciencias de la Vida, Universidad Andrés, Bello, Chile
| | - Carlos González
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile
| | - Ramón Latorre
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile.
| | - Yolima P Torres
- Departamento de Nutrición y Bioquímica, Facultad de Ciencias, Pontificia Universidad Javeriana, Bogotá, Colombia.
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4
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Zhao Y, Ge J, Li X, Guo Q, Zhu Y, Song J, Zhang L, Ding S, Yang X, Li R. Vasodilatory effect of formaldehyde via the NO/cGMP pathway and the regulation of expression of K ATP, BK Ca and L-type Ca 2+ channels. Toxicol Lett 2019; 312:55-64. [PMID: 30974163 DOI: 10.1016/j.toxlet.2019.04.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2019] [Revised: 03/28/2019] [Accepted: 04/06/2019] [Indexed: 12/12/2022]
Abstract
Formaldehyde (FA), a well-known toxic gas molecule similar to nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H2S), is widely produced endogenously via numerous biochemical pathways, and has a number of physiological roles in the biosystem. We attempted to investigate the vasorelaxant effects of FA and their underlying mechanisms. We found that FA induced vasorelaxant effects on rat aortic rings in a concentration-dependent manner. The NO/cyclic guanosine 5' monophosphate (cGMP) pathway was up-regulated when the rat aortas were treated with FA. The expression of large-conductance Ca2+-activated K+ (BKCa) channel subunits α and β of the rat aortas was increased by FA. Similarly, the levels of ATP-sensitive K+ (KATP) channel subunits Kir6.1 and Kir6.2 were also up-regulated when the rat aortas were incubated with FA. In contrast, levels of the L-type Ca2+ channel (LTCC) subunits, Cav1.2 and Cav1.3, decreased dramatically with increasing concentrations of FA. We demonstrated that the regulation of FA on vascular contractility may be via the up-regulation of the NO/cGMP pathway and the modulation of ion channels, including the upregulated expression of the KATP and BKCa channels and the inhibited expression of LTCCs. Further study is needed to explore the in-depth mechanisms of FA induced vasorelaxation.
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Affiliation(s)
- Yun Zhao
- Hubei Key Laboratory of Genetic Regulation and Integrative Biology, School of Life Sciences, Central China Normal University, 152 Luoyu Road, Wuhan 430079, PR China
| | - Jing Ge
- Hubei Key Laboratory of Genetic Regulation and Integrative Biology, School of Life Sciences, Central China Normal University, 152 Luoyu Road, Wuhan 430079, PR China
| | - Xiaoxiao Li
- Hubei Key Laboratory of Genetic Regulation and Integrative Biology, School of Life Sciences, Central China Normal University, 152 Luoyu Road, Wuhan 430079, PR China
| | - Qing Guo
- Hubei Key Laboratory of Genetic Regulation and Integrative Biology, School of Life Sciences, Central China Normal University, 152 Luoyu Road, Wuhan 430079, PR China; School of Public Health, Huazhong University of Science and Technology, Hangkong Road, Wuhan, 430030, PR China
| | - Yuqing Zhu
- Centre of Stem Cell and Regenerative medicine, School of Medicine, Zhejiang University, 866 Yuhangtang Road, Hangzhou, 310058, PR China
| | - Jing Song
- Hubei Key Laboratory of Genetic Regulation and Integrative Biology, School of Life Sciences, Central China Normal University, 152 Luoyu Road, Wuhan 430079, PR China
| | - Luoping Zhang
- Division of Environmental Health Sciences, School of Public Health, University of California, Berkeley, CA, 94720, USA
| | - Shumao Ding
- Hubei Key Laboratory of Genetic Regulation and Integrative Biology, School of Life Sciences, Central China Normal University, 152 Luoyu Road, Wuhan 430079, PR China
| | - Xu Yang
- Hubei Key Laboratory of Genetic Regulation and Integrative Biology, School of Life Sciences, Central China Normal University, 152 Luoyu Road, Wuhan 430079, PR China.
| | - Rui Li
- Hubei Key Laboratory of Genetic Regulation and Integrative Biology, School of Life Sciences, Central China Normal University, 152 Luoyu Road, Wuhan 430079, PR China.
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5
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Carrasquel-Ursulaez W, Alvarez O, Bezanilla F, Latorre R. Determination of the Stoichiometry between α- and γ1 Subunits of the BK Channel Using LRET. Biophys J 2018; 114:2493-2497. [PMID: 29705199 DOI: 10.1016/j.bpj.2018.04.008] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2018] [Revised: 03/20/2018] [Accepted: 04/05/2018] [Indexed: 11/18/2022] Open
Abstract
Two families of accessory proteins, β and γ, modulate BK channel gating and pharmacology. Notably, in the absence of internal Ca2+, the γ1 subunit promotes a large shift of the BK conductance-voltage curve to more negative potentials. However, very little is known about how α- and γ1 subunits interact. In particular, the association stoichiometry between both subunits is unknown. Here, we propose a method to answer this question using lanthanide resonance energy transfer. The method assumes that the kinetics of lanthanide resonance energy transfer-sensitized emission of the donor double-labeled α/γ1 complex is the linear combination of the kinetics of the sensitized emission in single-labeled complexes. We used a lanthanide binding tag engineered either into the α- or the γ1 subunits to bind Tb+3 as the donor. The acceptor (BODIPY) was attached to the BK pore-blocker iberiotoxin. We determined that γ1 associates with the α-subunit with a maximal 1:1 stoichiometry. This method could be applied to determine the stoichiometry of association between proteins within heteromultimeric complexes.
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Affiliation(s)
- Willy Carrasquel-Ursulaez
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso, Valparaíso, Chile
| | - Osvaldo Alvarez
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso, Valparaíso, Chile; Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago, Chile
| | - Francisco Bezanilla
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso, Valparaíso, Chile; Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois; Institute for Biophysical Dynamics, University of Chicago, Chicago, Illinois
| | - Ramon Latorre
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso, Valparaíso, Chile.
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6
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Pratt CP, Kuljis DA, Homanics GE, He J, Kolodieznyi D, Dudem S, Hollywood MA, Barth AL, Bruchez MP. Tagging of Endogenous BK Channels with a Fluorogen-Activating Peptide Reveals β4-Mediated Control of Channel Clustering in Cerebellum. Front Cell Neurosci 2017; 11:337. [PMID: 29163049 PMCID: PMC5671578 DOI: 10.3389/fncel.2017.00337] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2017] [Accepted: 10/12/2017] [Indexed: 01/10/2023] Open
Abstract
BK channels are critical regulators of neuronal activity, controlling firing, neurotransmitter release, cerebellar function, and BK channel mutations have been linked to seizure disorders. Modulation of BK channel gating is well characterized, regulated by accessory subunit interactions, intracellular signaling pathways, and membrane potential. In contrast, the role of intracellular trafficking mechanisms in controlling BK channel function, especially in live cells, has been less studied. Fluorogen-activating peptides (FAPs) are well-suited for trafficking and physiological studies due to the binding of malachite green (MG)-based dyes with sub-nanomolar affinity to the FAP, resulting in bright, photostable, far-red fluorescence. Cell-excluded MG dyes enable the selective tagging of surface protein and tracking through endocytic pathways. We used CRISPR to insert the FAP at the extracellular N-terminus of BKα in the first exon of its native locus, enabling regulation by the native promoter elements and tag incorporation into multiple splice isoforms. Motor coordination was found to be normal; however, BK channel expression seems to be reduced in some locations. Alternate start site selection or post-translational proteolytic processing resulted in incomplete FAP tagging of the BKα proteins in brain tissues. In Purkinje cell somata, FAP revealed BK channel clustering previously only observed by electron microscopy. Measurement of these clusters in β4+/- and β4-/- mice showed that puncta number and cluster fluorescence intensity on the soma are reduced in β4-/- knockout animals. This novel mouse line provides a versatile fluorescent platform for studying endogenous BK channels in living and fixed tissues. Future studies could apply this line to ex vivo neuronal cultures to study live-cell channel trafficking.
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Affiliation(s)
- Christopher P Pratt
- Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA, United States.,Molecular Biosensor and Imaging Center, Carnegie Mellon University, Pittsburgh, PA, United States.,Center for the Neural Basis of Cognition, Carnegie Mellon University, Pittsburgh, PA, United States
| | - Dika A Kuljis
- Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA, United States
| | - Gregg E Homanics
- Department of Anesthesiology, University of Pittsburgh, Pittsburgh, PA, United States.,Department of Neurobiology, University of Pittsburgh, Pittsburgh, PA, United States.,Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, PA, United States
| | - Jianjun He
- Molecular Biosensor and Imaging Center, Carnegie Mellon University, Pittsburgh, PA, United States.,Department of Chemistry, Carnegie Mellon University, Pittsburgh, PA, United States
| | - Dmytro Kolodieznyi
- Molecular Biosensor and Imaging Center, Carnegie Mellon University, Pittsburgh, PA, United States.,Department of Chemistry, Carnegie Mellon University, Pittsburgh, PA, United States
| | - Srikanth Dudem
- Smooth Muscle Research Centre, Dundalk Institute of Technology, Dundalk, Ireland
| | - Mark A Hollywood
- Smooth Muscle Research Centre, Dundalk Institute of Technology, Dundalk, Ireland
| | - Alison L Barth
- Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA, United States.,Center for the Neural Basis of Cognition, Carnegie Mellon University, Pittsburgh, PA, United States
| | - Marcel P Bruchez
- Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA, United States.,Molecular Biosensor and Imaging Center, Carnegie Mellon University, Pittsburgh, PA, United States.,Department of Chemistry, Carnegie Mellon University, Pittsburgh, PA, United States
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7
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Wang Y, Sun HY, Liu YG, Song Z, She G, Xiao GS, Wang Y, Li GR, Deng XL. Tyrphostin AG556 increases the activity of large conductance Ca 2+ -activated K + channels by inhibiting epidermal growth factor receptor tyrosine kinase. J Cell Mol Med 2017; 21:1826-1834. [PMID: 28294531 PMCID: PMC5571560 DOI: 10.1111/jcmm.13103] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2016] [Accepted: 12/28/2016] [Indexed: 01/08/2023] Open
Abstract
The present study was designed to investigate whether large conductance Ca2+‐activated K+ (BK) channels were regulated by epidermal growth factor (EGF) receptor (EGFR) tyrosine kinase. BK current and channel tyrosine phosphorylation level were measured in BK‐HEK 293 cells expressing both functional α‐subunits and the auxiliary β1‐subunits using electrophysiology, immunoprecipitation and Western blotting approaches, respectively, and the function of rat cerebral basilar arteries was determined with a wire myography system. We found that BK current in BK‐HEK 293 cells was increased by the broad spectrum protein tyrosine kinase (PTK) inhibitor genistein and the selective EGFR tyrosine kinase inhibitor AG556, one of the known tyrphostin. The effect of genistein or AG556 was antagonized by the protein tyrosine phosphatase (PTP) inhibitor orthovanadate. On the other hand, orthovanadate or EGF decreased BK current, and the effect was counteracted by AG556. The tyrosine phosphorylation level of BK channels (α‐ and β1‐subunits) was increased by EGF and orthovanadate, while decreased by genistein and AG556, and the reduced tyrosine phosphorylation of BK channels by genistein or AG556 was reversed by orthovanadate. Interestingly, AG556 induced a remarkable enhancement of BK current in rat cerebral artery smooth muscle cells and relaxation of pre‐contracted rat cerebral basilar arteries with denuded endothelium, and these effects were antagonized by the BK channel blocker paxilline or orthovanadate. These results demonstrate that tyrosine phosphorylation of BK channels by EGFR kinase decreases the channel activity, and inhibition of EGFR kinase by AG556 enhances the channel activity and dilates rat cerebral basilar arteries.
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Affiliation(s)
- Yan Wang
- Department of Physiology and Pathophysiology, School of Basic Medical Sciences, Xi'an Jiaotong University Health Science Center, Xi'an, Shaanxi, China.,Department of Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China
| | - Hai-Ying Sun
- Department of Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China
| | - Ying-Guang Liu
- Institute of Basic Medical Sciences, Xi'an Medical University, Xi'an, Shaanxi, China
| | - Zheng Song
- Department of Physiology and Pathophysiology, School of Basic Medical Sciences, Xi'an Jiaotong University Health Science Center, Xi'an, Shaanxi, China
| | - Gang She
- Department of Physiology and Pathophysiology, School of Basic Medical Sciences, Xi'an Jiaotong University Health Science Center, Xi'an, Shaanxi, China
| | - Guo-Sheng Xiao
- Xiamen Cardiovascular Hospital, Xiamen University, Xiamen, Fujian, China
| | - Yan Wang
- Xiamen Cardiovascular Hospital, Xiamen University, Xiamen, Fujian, China
| | - Gui-Rong Li
- Department of Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China.,Xiamen Cardiovascular Hospital, Xiamen University, Xiamen, Fujian, China
| | - Xiu-Ling Deng
- Department of Physiology and Pathophysiology, School of Basic Medical Sciences, Xi'an Jiaotong University Health Science Center, Xi'an, Shaanxi, China.,Cardiovascular Research Centre, School of Basic Medical Sciences, Xi'an Jiaotong University Health Science Center, Xi'an, Shaanxi, China
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8
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Overexcited MaxiK and K ATP channels underlie obstructive jaundice-induced vasoconstrictor hyporeactivity of arterial smooth muscle. Sci Rep 2016; 6:39246. [PMID: 28000721 PMCID: PMC5175282 DOI: 10.1038/srep39246] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2016] [Accepted: 11/21/2016] [Indexed: 01/14/2023] Open
Abstract
Substantial evidence has shown that obstructive jaundice can induce vascular hyporesponsiveness. The present study was designed to investigate mechanisms of MaxiK channel and KATP underlying cholestasis-induced vascular dysfunction. The isolated thoracic aorta was used to explore norepinephrine (NE)-induced contraction. The function of MaxiK and KATP channels were investigated using whole-cell patch clamp recording. Compared with Sham group, NE-induced vascular contraction was blunted after bile duct ligation (BDL), which could not be ameliorated significantly after endothelial denudation. Charybdotoxin and glibenclamide induced a more pronounced recovery from vascular hyporesponsiveness to NE in BDL group compared with Sham group. BDL significantly promoted the charybdotoxin sensitive MaxiK current and KATP current in isolated aortic smooth muscle cells. In addition, the expression of auxiliary subunits (MaxiK-β1 and SUR2B) rather pore-forming subunits (MaxiK-α and Kir6.1) was significantly up-regulated after BDL. These findings suggest that MaxiK and KATP channels play an important role in regulating vascular hyporesponsiveness in BDL rats.
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9
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Li N, Liu B, Xiang S, Shi L. Similar enhancement of BK(Ca) channel function despite different aerobic exercise frequency in aging cerebrovascular myocytes. Physiol Res 2016; 65:447-59. [PMID: 27070745 DOI: 10.33549/physiolres.933111] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
Aerobic exercise showed beneficial influence on cardiovascular systems in aging, and mechanisms underlying vascular adaption remain unclear. Large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels play critical roles in regulating cellular excitability and vascular tone. This study determined the effects of aerobic exercise on aging-associated functional changes in BK(Ca) channels in cerebrovascular myocytes, Male Wistar rats aged 20-22 months were randomly assigned to sedentary (O-SED), low training frequency (O-EXL), and high training frequency group (O-EXH). Young rats were used as control. Compared to young rats, whole-cell BK(Ca) current was decreased, and amplitude of spontaneous transient outward currents were reduced. The open probability and Ca(2+)/voltage sensitivity of single BK(Ca) channel were declined in O-SED, accompanied with a reduction of tamoxifen-induced BK(Ca) activation; the mean open time of BK(Ca) channels was shortened whereas close time was prolonged. Aerobic exercise training markedly alleviated the aging-associated decline independent of training frequency. Exercise three times rather than five times weekly may be a time and cost-saving training volume required to offer beneficial effects to offset the functional declines of BK(Ca) during aging.
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Affiliation(s)
- N Li
- Institute for Fetology, First Hospital of Soochow University, Suzhou, China, Department of Exercise Physiology, Beijing Sport University, Beijing, China.
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10
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β1-subunit-induced structural rearrangements of the Ca2+- and voltage-activated K+ (BK) channel. Proc Natl Acad Sci U S A 2016; 113:E3231-9. [PMID: 27217576 DOI: 10.1073/pnas.1606381113] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Large-conductance Ca(2+)- and voltage-activated K(+) (BK) channels are involved in a large variety of physiological processes. Regulatory β-subunits are one of the mechanisms responsible for creating BK channel diversity fundamental to the adequate function of many tissues. However, little is known about the structure of its voltage sensor domain. Here, we present the external architectural details of BK channels using lanthanide-based resonance energy transfer (LRET). We used a genetically encoded lanthanide-binding tag (LBT) to bind terbium as a LRET donor and a fluorophore-labeled iberiotoxin as the LRET acceptor for measurements of distances within the BK channel structure in a living cell. By introducing LBTs in the extracellular region of the α- or β1-subunit, we determined (i) a basic extracellular map of the BK channel, (ii) β1-subunit-induced rearrangements of the voltage sensor in α-subunits, and (iii) the relative position of the β1-subunit within the α/β1-subunit complex.
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11
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Bae H, Lee D, Kim YW, Choi J, Lee HJ, Kim SW, Kim T, Noh YH, Ko JH, Bang H, Lim I. Effects of hydrogen peroxide on voltage-dependent K(+) currents in human cardiac fibroblasts through protein kinase pathways. THE KOREAN JOURNAL OF PHYSIOLOGY & PHARMACOLOGY : OFFICIAL JOURNAL OF THE KOREAN PHYSIOLOGICAL SOCIETY AND THE KOREAN SOCIETY OF PHARMACOLOGY 2016; 20:315-24. [PMID: 27162486 PMCID: PMC4860374 DOI: 10.4196/kjpp.2016.20.3.315] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/08/2016] [Revised: 04/01/2016] [Accepted: 04/04/2016] [Indexed: 01/29/2023]
Abstract
Human cardiac fibroblasts (HCFs) have various voltage-dependent K(+) channels (VDKCs) that can induce apoptosis. Hydrogen peroxide (H2O2) modulates VDKCs and induces oxidative stress, which is the main contributor to cardiac injury and cardiac remodeling. We investigated whether H2O2 could modulate VDKCs in HCFs and induce cell injury through this process. In whole-cell mode patch-clamp recordings, application of H2O2 stimulated Ca(2+)-activated K(+) (KCa) currents but not delayed rectifier K(+) or transient outward K(+) currents, all of which are VDKCs. H2O2-stimulated KCa currents were blocked by iberiotoxin (IbTX, a large conductance KCa blocker). The H2O2-stimulating effect on large-conductance KCa (BKCa) currents was also blocked by KT5823 (a protein kinase G inhibitor) and 1 H-[1, 2, 4] oxadiazolo-[4, 3-a] quinoxalin-1-one (ODQ, a soluble guanylate cyclase inhibitor). In addition, 8-bromo-cyclic guanosine 3', 5'-monophosphate (8-Br-cGMP) stimulated BKCa currents. In contrast, KT5720 and H-89 (protein kinase A inhibitors) did not block the H2O2-stimulating effect on BKCa currents. Using RT-PCR and western blot analysis, three subtypes of KCa channels were detected in HCFs: BKCa channels, small-conductance KCa (SKCa) channels, and intermediate-conductance KCa (IKCa) channels. In the annexin V/propidium iodide assay, apoptotic changes in HCFs increased in response to H2O2, but IbTX decreased H2O2-induced apoptosis. These data suggest that among the VDKCs of HCFs, H2O2 only enhances BKCa currents through the protein kinase G pathway but not the protein kinase A pathway, and is involved in cell injury through BKCa channels.
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Affiliation(s)
- Hyemi Bae
- Department of Physiology, College of Medicine, Chung-Ang University, Seoul 06974, Korea
| | - Donghee Lee
- Department of Physiology, College of Medicine, Chung-Ang University, Seoul 06974, Korea
| | - Young-Won Kim
- Department of Physiology, College of Medicine, Chung-Ang University, Seoul 06974, Korea
| | - Jeongyoon Choi
- Department of Physiology, College of Medicine, Chung-Ang University, Seoul 06974, Korea
| | - Hong Jun Lee
- Biomedical Research Institute, College of Medicine, Chung-Ang University, Seoul 06974, Korea
| | - Sang-Wook Kim
- Department of Internal Medicine, College of Medicine, Chung-Ang University, Seoul 06974, Korea
| | - Taeho Kim
- Department of Internal Medicine, College of Medicine, Chung-Ang University, Seoul 06974, Korea
| | - Yun-Hee Noh
- Department of Biochemistry, School of Medicine, Konkuk University, Seoul 05029, Korea
| | - Jae-Hong Ko
- Department of Physiology, College of Medicine, Chung-Ang University, Seoul 06974, Korea
| | - Hyoweon Bang
- Department of Physiology, College of Medicine, Chung-Ang University, Seoul 06974, Korea
| | - Inja Lim
- Department of Physiology, College of Medicine, Chung-Ang University, Seoul 06974, Korea
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12
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Pratt CP, He J, Wang Y, Barth AL, Bruchez MP. Fluorogenic Green-Inside Red-Outside (GIRO) Labeling Approach Reveals Adenylyl Cyclase-Dependent Control of BKα Surface Expression. Bioconjug Chem 2015; 26:1963-71. [PMID: 26301573 PMCID: PMC4576318 DOI: 10.1021/acs.bioconjchem.5b00409] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
![]()
The
regulation of surface levels of protein is critical for proper
cell function and influences properties including cell adhesion, ion
channel contributions to current flux, and the sensitivity of surface
receptors to ligands. Here we demonstrate a two-color labeling system
in live cells using a single fluorogen activating peptide (FAP) based
fusion tag, which enables the rapid and simultaneous quantification
of surface and internal proteins. In the nervous system, BK channels
can regulate neural excitability and neurotransmitter release, and
the surface trafficking of BK channels can be modulated by signaling
cascades and assembly with accessory proteins. Using this labeling
approach, we examine the dynamics of BK channel surface expression
in HEK293 cells. Surface pools of the pore-forming BKα subunit
were stable, exhibiting a plasma membrane half-life of >10 h. Long-term
activation of adenylyl cyclase by forskolin reduced BKα surface
levels by 30%, an effect that could not be attributed to increased
bulk endocytosis of plasma membrane proteins. This labeling approach
is compatible with microscopic imaging and flow cytometry, providing
a solid platform for examining protein trafficking in living cells.
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Affiliation(s)
- Christopher P Pratt
- Department of Biological Sciences, ‡Department of Chemistry, §Molecular Biosensor and Imaging Center, and #Center for the Neural Basis of Cognition, Carnegie Mellon University , 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, United States
| | - Jianjun He
- Department of Biological Sciences, ‡Department of Chemistry, §Molecular Biosensor and Imaging Center, and #Center for the Neural Basis of Cognition, Carnegie Mellon University , 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, United States
| | - Yi Wang
- Department of Biological Sciences, ‡Department of Chemistry, §Molecular Biosensor and Imaging Center, and #Center for the Neural Basis of Cognition, Carnegie Mellon University , 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, United States
| | - Alison L Barth
- Department of Biological Sciences, ‡Department of Chemistry, §Molecular Biosensor and Imaging Center, and #Center for the Neural Basis of Cognition, Carnegie Mellon University , 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, United States
| | - Marcel P Bruchez
- Department of Biological Sciences, ‡Department of Chemistry, §Molecular Biosensor and Imaging Center, and #Center for the Neural Basis of Cognition, Carnegie Mellon University , 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, United States
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13
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Carrasquel-Ursulaez W, Contreras GF, Sepúlveda RV, Aguayo D, González-Nilo F, González C, Latorre R. Hydrophobic interaction between contiguous residues in the S6 transmembrane segment acts as a stimuli integration node in the BK channel. ACTA ACUST UNITED AC 2015; 145:61-74. [PMID: 25548136 PMCID: PMC4278184 DOI: 10.1085/jgp.201411194] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Phenylalanine 380 and leucine 377 in the BK channel S6 transmembrane helix of contiguous subunits participate in a hydrophobic interaction in both the closed and open state; this interaction is important in the allosteric coupling between the Ca2+ and voltage sensors and pore domain. Large-conductance Ca2+- and voltage-activated K+ channel (BK) open probability is enhanced by depolarization, increasing Ca2+ concentration, or both. These stimuli activate modular voltage and Ca2+ sensors that are allosterically coupled to channel gating. Here, we report a point mutation of a phenylalanine (F380A) in the S6 transmembrane helix that, in the absence of internal Ca2+, profoundly hinders channel opening while showing only minor effects on the voltage sensor active–resting equilibrium. Interpretation of these results using an allosteric model suggests that the F380A mutation greatly increases the free energy difference between open and closed states and uncouples Ca2+ binding from voltage sensor activation and voltage sensor activation from channel opening. However, the presence of a bulky and more hydrophobic amino acid in the F380 position (F380W) increases the intrinsic open–closed equilibrium, weakening the coupling between both sensors with the pore domain. Based on these functional experiments and molecular dynamics simulations, we propose that F380 interacts with another S6 hydrophobic residue (L377) in contiguous subunits. This pair forms a hydrophobic ring important in determining the open–closed equilibrium and, like an integration node, participates in the communication between sensors and between the sensors and pore. Moreover, because of its effects on open probabilities, the F380A mutant can be used for detailed voltage sensor experiments in the presence of permeant cations.
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Affiliation(s)
- Willy Carrasquel-Ursulaez
- Centro Interdisciplinario de Neurociencia de Valparaíso and Doctorado en Ciencias Mención Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso 2366103, Chile Centro Interdisciplinario de Neurociencia de Valparaíso and Doctorado en Ciencias Mención Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso 2366103, Chile
| | - Gustavo F Contreras
- Centro Interdisciplinario de Neurociencia de Valparaíso and Doctorado en Ciencias Mención Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso 2366103, Chile
| | - Romina V Sepúlveda
- Centro de Bioinformática y Biología Integrativa and Doctorado en Biotecnología, Facultad de Ciencias Biológicas, Universidad Andres Bello, Santiago 8370146, Chile Centro de Bioinformática y Biología Integrativa and Doctorado en Biotecnología, Facultad de Ciencias Biológicas, Universidad Andres Bello, Santiago 8370146, Chile
| | - Daniel Aguayo
- Centro de Bioinformática y Biología Integrativa and Doctorado en Biotecnología, Facultad de Ciencias Biológicas, Universidad Andres Bello, Santiago 8370146, Chile
| | - Fernando González-Nilo
- Centro Interdisciplinario de Neurociencia de Valparaíso and Doctorado en Ciencias Mención Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso 2366103, Chile Centro de Bioinformática y Biología Integrativa and Doctorado en Biotecnología, Facultad de Ciencias Biológicas, Universidad Andres Bello, Santiago 8370146, Chile
| | - Carlos González
- Centro Interdisciplinario de Neurociencia de Valparaíso and Doctorado en Ciencias Mención Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso 2366103, Chile
| | - Ramón Latorre
- Centro Interdisciplinario de Neurociencia de Valparaíso and Doctorado en Ciencias Mención Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso 2366103, Chile
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14
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Yang H, Zhang G, Cui J. BK channels: multiple sensors, one activation gate. Front Physiol 2015; 6:29. [PMID: 25705194 PMCID: PMC4319557 DOI: 10.3389/fphys.2015.00029] [Citation(s) in RCA: 77] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2015] [Accepted: 01/19/2015] [Indexed: 01/01/2023] Open
Abstract
Ion transport across cell membranes is essential to cell communication and signaling. Passive ion transport is mediated by ion channels, membrane proteins that create ion conducting pores across cell membrane to allow ion flux down electrochemical gradient. Under physiological conditions, majority of ion channel pores are not constitutively open. Instead, structural region(s) within these pores breaks the continuity of the aqueous ion pathway, thereby serves as activation gate(s) to control ions flow in and out. To achieve spatially and temporally regulated ion flux in cells, many ion channels have evolved sensors to detect various environmental stimuli or the metabolic states of the cell and trigger global conformational changes, thereby dynamically operate the opening and closing of their activation gate. The sensors of ion channels can be broadly categorized as chemical sensors and physical sensors to respond to chemical (such as neural transmitters, nucleotides and ions) and physical (such as voltage, mechanical force and temperature) signals, respectively. With the rapidly growing structural and functional information of different types of ion channels, it is now critical to understand how ion channel sensors dynamically control their gates at molecular and atomic level. The voltage and Ca2+ activated BK channels, a K+ channel with an electrical sensor and multiple chemical sensors, provide a unique model system for us to understand how physical and chemical energy synergistically operate its activation gate.
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Affiliation(s)
- Huanghe Yang
- Ion Channel Research Unit, Duke University Medical Center Durham, NC, USA ; Department of Biochemistry, Duke University Medical Center Durham, NC, USA
| | - Guohui Zhang
- Department of Biomedical Engineering, Washington University in Saint Louis St. Louis, MO, USA
| | - Jianmin Cui
- Department of Biomedical Engineering, Washington University in Saint Louis St. Louis, MO, USA ; Cardiac Bioelectricity and Arrhythmia Center, Washington University in Saint Louis St. Louis, MO, USA ; Center for The Investigation of Membrane Excitability Disorders, Washington University in Saint Louis St. Louis, MO, USA
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15
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Dopico AM, Bukiya AN, Martin GE. Ethanol modulation of mammalian BK channels in excitable tissues: molecular targets and their possible contribution to alcohol-induced altered behavior. Front Physiol 2014; 5:466. [PMID: 25538625 PMCID: PMC4256990 DOI: 10.3389/fphys.2014.00466] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2014] [Accepted: 11/13/2014] [Indexed: 11/30/2022] Open
Abstract
In most tissues, the function of Ca2+- and voltage-gated K+ (BK) channels is modified in response to ethanol concentrations reached in human blood during alcohol intoxication. In general, modification of BK current from ethanol-naïve preparations in response to brief ethanol exposure results from changes in channel open probability without modification of unitary conductance or change in BK protein levels in the membrane. Protracted and/or repeated ethanol exposure, however, may evoke changes in BK expression. The final ethanol effect on BK open probability leading to either BK current potentiation or BK current reduction is determined by an orchestration of molecular factors, including levels of activating ligand (Ca2+i), BK subunit composition and post-translational modifications, and the channel's lipid microenvironment. These factors seem to allosterically regulate a direct interaction between ethanol and a recognition pocket of discrete dimensions recently mapped to the channel-forming (slo1) subunit. Type of ethanol exposure also plays a role in the final BK response to the drug: in several central nervous system regions (e.g., striatum, primary sensory neurons, and supraoptic nucleus), acute exposure to ethanol reduces neuronal excitability by enhancing BK activity. In contrast, protracted or repetitive ethanol administration may alter BK subunit composition and membrane expression, rendering the BK complex insensitive to further ethanol exposure. In neurohypophyseal axon terminals, ethanol potentiation of BK channel activity leads to a reduction in neuropeptide release. In vascular smooth muscle, however, ethanol inhibition of BK current leads to cell contraction and vascular constriction.
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Affiliation(s)
- Alex M Dopico
- Department of Pharmacology, College of Medicine, The University of Tennessee Health Science Center Memphis, TN, USA
| | - Anna N Bukiya
- Department of Pharmacology, College of Medicine, The University of Tennessee Health Science Center Memphis, TN, USA
| | - Gilles E Martin
- Department of Psychiatry, The University of Massachusetts Medical School Worcester, MA, USA
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16
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Liu Y, Song X, Shi Y, Shi Z, Niu W, Feng X, Gu D, Bao HF, Ma HP, Eaton DC, Zhuang J, Cai H. WNK1 activates large-conductance Ca2+-activated K+ channels through modulation of ERK1/2 signaling. J Am Soc Nephrol 2014; 26:844-54. [PMID: 25145935 DOI: 10.1681/asn.2014020186] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
With no lysine (WNK) kinases are members of the serine/threonine kinase family. We previously showed that WNK4 inhibits renal large-conductance Ca(2+)-activated K(+) (BK) channel activity by enhancing its degradation through a lysosomal pathway. In this study, we investigated the effect of WNK1 on BK channel activity. In HEK293 cells stably expressing the α subunit of BK (HEK-BKα cells), siRNA-mediated knockdown of WNK1 expression significantly inhibited both BKα channel activity and open probability. Knockdown of WNK1 expression also significantly inhibited BKα protein expression and increased ERK1/2 phosphorylation, whereas overexpression of WNK1 significantly enhanced BKα expression and decreased ERK1/2 phosphorylation in a dose-dependent manner in HEK293 cells. Knockdown of ERK1/2 prevented WNK1 siRNA-mediated inhibition of BKα expression. Similarly, pretreatment of HEK-BKα cells with the lysosomal inhibitor bafilomycin A1 reversed the inhibitory effects of WNK1 siRNA on BKα expression in a dose-dependent manner. Knockdown of WNK1 expression also increased the ubiquitination of BKα channels. Notably, mice fed a high-K(+) diet for 10 days had significantly higher renal protein expression levels of BKα and WNK1 and lower levels of ERK1/2 phosphorylation compared with mice fed a normal-K(+) diet. These data suggest that WNK1 enhances BK channel function by reducing ERK1/2 signaling-mediated lysosomal degradation of the channel.
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Affiliation(s)
- Yingli Liu
- Renal Division, Department of Medicine, and Department of Nephrology, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine
| | - Xiang Song
- Department of Cardiology, The Fourth Affiliated Hospital, Harbin Medical University, Heilongjiang, China; and
| | | | - Zhen Shi
- Department of Nephrology, The Second Affiliated Hospital, Wenzhou Medical University, Zhejiang, China
| | - Weihui Niu
- Department of Nephrology, The Second Affiliated Hospital, Wenzhou Medical University, Zhejiang, China
| | - Xiuyan Feng
- Renal Division, Department of Medicine, and Renal Section, Atlanta Veterans Affairs Medical Center, Decatur, Georgia
| | - Dingying Gu
- Department of Nephrology, The Second Affiliated Hospital, Wenzhou Medical University, Zhejiang, China
| | - Hui-Fang Bao
- Department of Physiology, Emory University School of Medicine, Atlanta, Georgia
| | - He-Ping Ma
- Department of Physiology, Emory University School of Medicine, Atlanta, Georgia
| | - Douglas C Eaton
- Department of Physiology, Emory University School of Medicine, Atlanta, Georgia
| | - Jieqiu Zhuang
- Department of Nephrology, The Second Affiliated Hospital, Wenzhou Medical University, Zhejiang, China;
| | - Hui Cai
- Renal Division, Department of Medicine, and Renal Section, Atlanta Veterans Affairs Medical Center, Decatur, Georgia Department of Physiology, Emory University School of Medicine, Atlanta, Georgia;
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17
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Li Y, Lorca RA, Ma X, Rhodes A, England SK. BK channels regulate myometrial contraction by modulating nuclear translocation of NF-κB. Endocrinology 2014; 155:3112-22. [PMID: 24914944 PMCID: PMC4098006 DOI: 10.1210/en.2014-1152] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The large-conductance Ca(2+)-activated K(+) (BK) channel plays an essential role in maintaining uterine quiescence during pregnancy. Growing evidence has shown a link between the BK channel and bacterial lipopolysaccharide (LPS)-induced nuclear factor-κB (NF-κB) activation in macrophages. In the uterus, NF-κB activation plays an important role in inflammatory processes that lead to parturition. Our objective was to determine whether the BK channel regulates uterine contraction, in part, by modulating NF-κB translocation into the nucleus. We compared the effects of BK channel modulation to those of LPS on NF-κB nuclear translocation and contraction in an immortalized human myometrial cell line (human telomerase reverse transcriptase [hTERT]) and uterine myocytes. Our results showed that BK channel inhibitors paxilline and penitrem A induced translocation of NF-κB into the nucleus in both hTERT cells and uterine myocytes to a similar extent as LPS treatment, and LPS and paxilline similarly reduced BK channel currents. Conversely, neither BK channel openers nor blockade of the small conductance Ca(2+)-activated K(+) channel protein 3 had an effect on NF-κB translocation. Additionally, collagen-based assays showed that paxilline induced contraction of hTERT cells and uterine myocytes. This was dependent upon cyclooxygenase-2 activity. Moreover, paxilline-induced contractility and increased cyclooxygenase-2 expression both depended on availability of free NF-κB. This study suggests that BK channels regulate myometrial contraction, in part, by modulating nuclear translocation of NF-κB.
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Affiliation(s)
- Youe Li
- Center for Women's Reproductive Sciences Research, Department of Obstetrics and Gynecology, Basic Science Division, Washington University in St Louis, St Louis, Missouri 63110
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18
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Venglovecz V, Rakonczay Z, Gray MA, Hegyi P. Potassium channels in pancreatic duct epithelial cells: their role, function and pathophysiological relevance. Pflugers Arch 2014; 467:625-40. [PMID: 25074489 DOI: 10.1007/s00424-014-1585-0] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2014] [Revised: 07/09/2014] [Accepted: 07/18/2014] [Indexed: 12/14/2022]
Abstract
Pancreatic ductal epithelial cells play a fundamental role in HCO3 (-) secretion, a process which is essential for maintaining the integrity of the pancreas. Although several studies have implicated impaired HCO3 (-) and fluid secretion as a triggering factor in the development of pancreatitis, the mechanism and regulation of HCO3 (-) secretion is still not completely understood. To date, most studies on the ion transporters that orchestrate ductal HCO3 (-) secretion have focussed on the role of Cl(-)/HCO3 (-) exchangers and Cl(-) channels, whereas much less is known about the role of K(+) channels. However, there is growing evidence that many types of K(+) channels are present in ductal cells where they have an essential role in establishing and maintaining the electrochemical driving force for anion secretion. For this reason, strategies that increase K(+) channel function may help to restore impaired HCO3 (-) and fluid secretion, such as in pancreatitis, and therefore provide novel directions for future pancreatic therapy. In this review, our aims are to summarize the types of K(+) channels found in pancreatic ductal cells and to discuss their individual roles in ductal HCO3 (-) secretion. We will also describe how K(+) channels are involved in pathophysiological conditions and discuss how they could act as new molecular targets for the development of therapeutic approaches to treat pancreatic diseases.
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Affiliation(s)
- Viktória Venglovecz
- Department of Pharmacology and Pharmacotherapy, University of Szeged, Szeged, Hungary,
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19
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Lorca RA, Prabagaran M, England SK. Functional insights into modulation of BKCa channel activity to alter myometrial contractility. Front Physiol 2014; 5:289. [PMID: 25132821 PMCID: PMC4116789 DOI: 10.3389/fphys.2014.00289] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2014] [Accepted: 07/14/2014] [Indexed: 12/15/2022] Open
Abstract
The large-conductance voltage- and Ca(2+)-activated K(+) channel (BKCa) is an important regulator of membrane excitability in a wide variety of cells and tissues. In myometrial smooth muscle, activation of BKCa plays essential roles in buffering contractility to maintain uterine quiescence during pregnancy and in the transition to a more contractile state at the onset of labor. Multiple mechanisms of modulation have been described to alter BKCa channel activity, expression, and cellular localization. In the myometrium, BKCa is regulated by alternative splicing, protein targeting to the plasma membrane, compartmentation in membrane microdomains, and posttranslational modifications. In addition, interaction with auxiliary proteins (i.e., β1- and β2-subunits), association with G-protein coupled receptor signaling pathways, such as those activated by adrenergic and oxytocin receptors, and hormonal regulation provide further mechanisms of variable modulation of BKCa channel function in myometrial smooth muscle. Here, we provide an overview of these mechanisms of BKCa channel modulation and provide a context for them in relation to myometrial function.
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Affiliation(s)
- Ramón A Lorca
- Department of Obstetrics and Gynecology, Washington University in St. Louis School of Medicine St. Louis, MO, USA
| | - Monali Prabagaran
- Department of Obstetrics and Gynecology, Washington University in St. Louis School of Medicine St. Louis, MO, USA
| | - Sarah K England
- Department of Obstetrics and Gynecology, Washington University in St. Louis School of Medicine St. Louis, MO, USA
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20
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Peng Z, Sakai Y, Kurgan L, Sokolowski B, Uversky V. Intrinsic disorder in the BK channel and its interactome. PLoS One 2014; 9:e94331. [PMID: 24727949 PMCID: PMC3984161 DOI: 10.1371/journal.pone.0094331] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2013] [Accepted: 03/12/2014] [Indexed: 11/18/2022] Open
Abstract
The large-conductance Ca2+-activated K+ (BK) channel is broadly expressed in various mammalian cells and tissues such as neurons, skeletal and smooth muscles, exocrine cells, and sensory cells of the inner ear. Previous studies suggest that BK channels are promiscuous binders involved in a multitude of protein-protein interactions. To gain a better understanding of the potential mechanisms underlying BK interactions, we analyzed the abundance, distribution, and potential mechanisms of intrinsic disorder in 27 BK channel variants from mouse cochlea, 104 previously reported BK-associated proteins (BKAPS) from cytoplasmic and membrane/cytoskeletal regions, plus BK β- and γ-subunits. Disorder was evaluated using the MFDp algorithm, which is a consensus-based predictor that provides a strong and competitive predictive quality and PONDR, which can determine long intrinsically disordered regions (IDRs). Disorder-based binding sites or molecular recognition features (MoRFs) were found using MoRFpred and ANCHOR. BKAP functions were categorized based on Gene Ontology (GO) terms. The analyses revealed that the BK variants contain a number of IDRs. Intrinsic disorder is also common in BKAPs, of which ∼5% are completely disordered. However, intrinsic disorder is very differently distributed within BK and its partners. Approximately 65% of the disordered segments in BK channels are long (IDRs) (>50 residues), whereas >60% of the disordered segments in BKAPs are short IDRs that range in length from 4 to 30 residues. Both α and γ subunits showed various amounts of disorder as did hub proteins of the BK interactome. Our analyses suggest that intrinsic disorder is important for the function of BK and its BKAPs. Long IDRs in BK are engaged in protein-protein and protein-ligand interactions, contain multiple post-translational modification sites, and are subjected to alternative splicing. The disordered structure of BK and its BKAPs suggests one of the underlying mechanisms of their interaction.
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Affiliation(s)
- Zhenling Peng
- Department of Electrical and Computer Engineering, University of Alberta, Edmonton, Alberta, Canada
| | - Yoshihisa Sakai
- Department of Otolaryngology - Head and Neck Surgery, Morsani College of Medicine, University of South Florida, Tampa, Florida, United States of America
| | - Lukasz Kurgan
- Department of Electrical and Computer Engineering, University of Alberta, Edmonton, Alberta, Canada
| | - Bernd Sokolowski
- Department of Otolaryngology - Head and Neck Surgery, Morsani College of Medicine, University of South Florida, Tampa, Florida, United States of America
| | - Vladimir Uversky
- Department of Molecular Medicine and Byrd Alzheimer's Research Institute, Morsani College of Medicine, University of South Florida, Tampa, Florida, United States of America; Department of Biological Sciences, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia; Institute for Biological Instrumentation, Russian Academy of Sciences, Pushchino, Moscow Region, Russia
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21
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Hristov KL, Smith AC, Parajuli SP, Malysz J, Petkov GV. Large-conductance voltage- and Ca2+-activated K+ channel regulation by protein kinase C in guinea pig urinary bladder smooth muscle. Am J Physiol Cell Physiol 2013; 306:C460-70. [PMID: 24352333 DOI: 10.1152/ajpcell.00325.2013] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Large-conductance voltage- and Ca(2+)-activated K(+) (BK) channels are critical regulators of detrusor smooth muscle (DSM) excitability and contractility. PKC modulates the contraction of DSM and BK channel activity in non-DSM cells; however, the cellular mechanism regulating the PKC-BK channel interaction in DSM remains unknown. We provide a novel mechanistic insight into BK channel regulation by PKC in DSM. We used patch-clamp electrophysiology, live-cell Ca(2+) imaging, and functional studies of DSM contractility to elucidate BK channel regulation by PKC at cellular and tissue levels. Voltage-clamp experiments showed that pharmacological activation of PKC with PMA inhibited the spontaneous transient BK currents in native freshly isolated guinea pig DSM cells. Current-clamp recordings revealed that PMA significantly depolarized DSM membrane potential and inhibited the spontaneous transient hyperpolarizations in DSM cells. The PMA inhibitory effects on DSM membrane potential were completely abolished by the selective BK channel inhibitor paxilline. Activation of PKC with PMA did not affect the amplitude of the voltage-step-induced whole cell steady-state BK current or the single BK channel open probability (recorded in cell-attached mode) upon inhibition of all major Ca(2+) sources for BK channel activation with thapsigargin, ryanodine, and nifedipine. PKC activation with PMA elevated intracellular Ca(2+) levels in DSM cells and increased spontaneous phasic and nerve-evoked contractions of DSM isolated strips. Our results support the concept that PKC activation leads to a reduction of BK channel activity in DSM via a Ca(2+)-dependent mechanism, thus increasing DSM contractility.
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Affiliation(s)
- Kiril L Hristov
- Department of Drug Discovery and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Columbia, South Carolina
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22
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Shi L, Liu B, Zhang Y, Xue Z, Liu Y, Chen Y. Exercise Training Reverses Unparallel Downregulation of MaxiK Channel - and 1-Subunit to Enhance Vascular Function in Aging Mesenteric Arteries. J Gerontol A Biol Sci Med Sci 2013; 69:1462-73. [DOI: 10.1093/gerona/glt205] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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23
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Wu W, Wang Y, Deng XL, Sun HY, Li GR. Cholesterol down-regulates BK channels stably expressed in HEK 293 cells. PLoS One 2013; 8:e79952. [PMID: 24260325 PMCID: PMC3832390 DOI: 10.1371/journal.pone.0079952] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2013] [Accepted: 09/28/2013] [Indexed: 12/23/2022] Open
Abstract
Cholesterol is one of the major lipid components of the plasma membrane in mammalian cells and is involved in the regulation of a number of ion channels. The present study investigates how large conductance Ca2+-activated K+ (BK) channels are regulated by membrane cholesterol in BK-HEK 293 cells expressing both the α-subunit hKCa1.1 and the auxiliary β1-subunit or in hKCa1.1-HEK 293 cells expressing only the α-subunit hKCa1.1 using approaches of electrophysiology, molecular biology, and immunocytochemistry. Membrane cholesterol was depleted in these cells with methyl-β-cyclodextrin (MβCD), and enriched with cholesterol-saturated MβCD (MβCD-cholesterol) or low-density lipoprotein (LDL). We found that BK current density was decreased by cholesterol enrichment in BK-HEK 293 cells, with a reduced expression of KCa1.1 protein, but not the β1-subunit protein. This effect was fully countered by the proteasome inhibitor lactacystin or the lysosome function inhibitor bafilomycin A1. Interestingly, in hKCa1.1-HEK 293 cells, the current density was not affected by cholesterol enrichment, but directly decreased by MβCD, suggesting that the down-regulation of BK channels by cholesterol depends on the auxiliary β1-subunit. The reduced KCa1.1 channel protein expression was also observed in cultured human coronary artery smooth muscle cells with cholesterol enrichment using MβCD-cholesterol or LDL. These results demonstrate the novel information that cholesterol down-regulates BK channels by reducing KCa1.1 protein expression via increasing the channel protein degradation, and the effect is dependent on the auxiliary β1-subunit.
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Affiliation(s)
- Wei Wu
- Department of Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong, China
| | - Yan Wang
- Department of Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong, China
- Department of Physiology and Pathophysiology, School of Medicine, Xi'an Jiaotong University, Xi'an, China
| | - Xiu-Ling Deng
- Department of Physiology and Pathophysiology, School of Medicine, Xi'an Jiaotong University, Xi'an, China
| | - Hai-Ying Sun
- Department of Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong, China
| | - Gui-Rong Li
- Department of Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong, China
- Department of Physiology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong, China
- * E-mail:
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24
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Park WS, Heo SC, Jeon ES, Hong DH, Son YK, Ko JH, Kim HK, Lee SY, Kim JH, Han J. Functional expression of smooth muscle-specific ion channels in TGF-β(1)-treated human adipose-derived mesenchymal stem cells. Am J Physiol Cell Physiol 2013; 305:C377-91. [PMID: 23761629 DOI: 10.1152/ajpcell.00404.2012] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Human adipose tissue-derived mesenchymal stem cells (hASCs) have the power to differentiate into various cell types including chondrocytes, osteocytes, adipocytes, neurons, cardiomyocytes, and smooth muscle cells. We characterized the functional expression of ion channels after transforming growth factor-β1 (TGF-β1)-induced differentiation of hASCs, providing insights into the differentiation of vascular smooth muscle cells. The treatment of hASCs with TGF-β1 dramatically increased the contraction of a collagen-gel lattice and the expression levels of specific genes for smooth muscle including α-smooth muscle actin, calponin, smooth mucle-myosin heavy chain, smoothelin-B, myocardin, and h-caldesmon. We observed Ca(2+), big-conductance Ca(2+)-activated K(+) (BKCa), and voltage-dependent K(+) (Kv) currents in TGF-β1-induced, differentiated hASCs and not in undifferentiated hASCs. The currents share the characteristics of vascular smooth muscle cells (SMCs). RT-PCR and Western blotting revealed that the L-type (Cav1.2) and T-type (Cav3.1, 3.2, and 3.3), known to be expressed in vascular SMCs, dramatically increased along with the Cavβ1 and Cavβ3 subtypes in TGF-β1-induced, differentiated hASCs. Although the expression-level changes of the β-subtype BKCa channels varied, the major α-subtype BKCa channel (KCa1.1) clearly increased in the TGF-β1-induced, differentiated hASCs. Most of the Kv subtypes, also known to be expressed in vascular SMCs, dramatically increased in the TGF-β1-induced, differentiated hASCs. Our results suggest that TGF-β1 induces the increased expression of vascular SMC-like ion channels and the differentiation of hASCs into contractile vascular SMCs.
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Affiliation(s)
- Won Sun Park
- Department of Physiology, Kangwon National University School of Medicine, Chuncheon, Korea
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25
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Molecular mechanisms of large-conductance ca (2+) -activated potassium channel activation by ginseng gintonin. EVIDENCE-BASED COMPLEMENTARY AND ALTERNATIVE MEDICINE 2013; 2013:323709. [PMID: 23662129 PMCID: PMC3638619 DOI: 10.1155/2013/323709] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/10/2013] [Revised: 03/05/2013] [Accepted: 03/12/2013] [Indexed: 01/12/2023]
Abstract
Gintonin is a unique lysophosphatidic acid (LPA) receptor ligand
found in Panax ginseng. Gintonin induces transient
[Ca2+]i
through G protein-coupled LPA receptors. Large-conductance Ca2+-activated
K+ (BKCa)
channels are expressed in blood vessels and neurons and
play important roles in blood vessel relaxation and attenuation of
neuronal excitability. BKCa channels are activated by transient
[Ca2+]i
and are regulated by various Ca2+-dependent kinases. We
investigated the molecular mechanisms of BKCa channel activation
by gintonin. BKCa channels are heterologously expressed in
Xenopus oocytes. Gintonin treatment induced BKCa channel activation in
oocytes expressing the BKCa channel α subunit in a
concentration-dependent manner (EC50 = 0.71 ± 0.08 µg/mL).
Gintonin-mediated BKCa channel activation was blocked by a PKC
inhibitor, calphostin, and by the calmodulin inhibitor,
calmidazolium. Site-directed mutations in BKCa channels targeting
CaM kinase II or PKC phosphorylation sites but not PKA
phosphorylation sites attenuated gintonin action. Mutations in the
Ca2+ bowl and the regulator of K+ conductance (RCK) site also
blocked gintonin action. These results indicate that
gintonin-mediated BKCa channel activations are achieved through
LPA1 receptor-phospholipase C-IP3-Ca2+-PKC-calmodulin-CaM kinase
II pathways and calcium binding to the Ca2+ bowl and RCK domain.
Gintonin could be a novel contributor against blood vessel
constriction and over-excitation of neurons.
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26
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State-dependent FRET reports calcium- and voltage-dependent gating-ring motions in BK channels. Proc Natl Acad Sci U S A 2013; 110:5217-22. [PMID: 23479636 DOI: 10.1073/pnas.1219611110] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Large-conductance voltage- and calcium-dependent potassium channels (BK, "Big K+") are important controllers of cell excitability. In the BK channel, a large C-terminal intracellular region containing a "gating-ring" structure has been proposed to transduce Ca(2+) binding into channel opening. Using patch-clamp fluorometry, we have investigated the calcium and voltage dependence of conformational changes of the gating-ring region of BK channels, while simultaneously monitoring channel conductance. Fluorescence resonance energy transfer (FRET) between fluorescent protein inserts indicates that Ca(2+) binding produces structural changes of the gating ring that are much larger than those predicted by current X-ray crystal structures of isolated gating rings.
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27
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Pantazis A, Olcese R. Relative transmembrane segment rearrangements during BK channel activation resolved by structurally assigned fluorophore-quencher pairing. ACTA ACUST UNITED AC 2012; 140:207-18. [PMID: 22802360 PMCID: PMC3409098 DOI: 10.1085/jgp.201210807] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Voltage-activated proteins can sense, and respond to, changes in the electric field pervading the cell membrane by virtue of a transmembrane helix bundle, the voltage-sensing domain (VSD). Canonical VSDs consist of four transmembrane helices (S1-S4) of which S4 is considered a principal component because it possesses charged residues immersed in the electric field. Membrane depolarization compels the charges, and by extension S4, to rearrange with respect to the field. The VSD of large-conductance voltage- and Ca-activated K(+) (BK) channels exhibits two salient inconsistencies from the canonical VSD model: (1) the BK channel VSD possesses an additional nonconserved transmembrane helix (S0); and (2) it exhibits a "decentralized" distribution of voltage-sensing charges, in helices S2 and S3, in addition to S4. Considering these unique features, the voltage-dependent rearrangements of the BK VSD could differ significantly from the standard model of VSD operation. To understand the mode of operation of this unique VSD, we have optically tracked the relative motions of the BK VSD transmembrane helices during activation, by manipulating the quenching environment of site-directed fluorescent labels with native and introduced Trp residues. Having previously reported that S0 and S4 diverge during activation, in this work we demonstrate that S4 also diverges from S1 and S2, whereas S2, compelled by its voltage-sensing charged residues, moves closer to S1. This information contributes spatial constraints for understanding the BK channel voltage-sensing process, revealing the structural rearrangements in a non-canonical VSD.
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Affiliation(s)
- Antonios Pantazis
- Department of Anesthesiology, Division of Molecular Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90075, USA
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28
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The first transmembrane domain (TM1) of β2-subunit binds to the transmembrane domain S1 of α-subunit in BK potassium channels. FEBS Lett 2012; 586:2287-93. [PMID: 22710124 DOI: 10.1016/j.febslet.2012.05.066] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2012] [Revised: 05/31/2012] [Accepted: 05/31/2012] [Indexed: 01/10/2023]
Abstract
The BK channel is one of the most broadly expressed ion channels in mammals. In many tissues, the BK channel pore-forming α-subunit is associated to an auxiliary β-subunit that modulates the voltage- and Ca(2+)-dependent activation of the channel. Structural components present in β-subunits that are important for the physical association with the α-subunit are yet unknown. Here, we show through co-immunoprecipitation that the intracellular C-terminus, the second transmembrane domain (TM2) and the extracellular loop of the β2-subunit are dispensable for association with the α-subunit pointing transmembrane domain 1 (TM1) as responsible for the interaction. Indeed, the TOXCAT assay for transmembrane protein-protein interactions demonstrated for the first time that TM1 of the β2-subunit physically binds to the transmembrane S1 domain of the α-subunit.
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29
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Zhuang J, Zhang X, Wang D, Li J, Zhou B, Shi Z, Gu D, Denson DD, Eaton DC, Cai H. WNK4 kinase inhibits Maxi K channel activity by a kinase-dependent mechanism. Am J Physiol Renal Physiol 2011; 301:F410-9. [PMID: 21613417 DOI: 10.1152/ajprenal.00518.2010] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
WNK [with no lysine (k)] kinase is a serine/threonine kinase subfamily. Mutations in two of the WNK kinases result in pseudohypoaldosteronism type II (PHA II) characterized by hypertension, hyperkalemia, and metabolic acidosis. Recent studies showed that both WNK1 and WNK4 inhibit ROMK activity. However, little is known about the effect of WNK kinases on Maxi K, a large-conductance Ca(2+) and voltage-activated potassium (K) channel. Here, we report that WNK4 wild-type (WT) significantly inhibits Maxi K channel activity in HEK αBK stable cell lines compared with the control group. However, a WNK4 dead-kinase mutant, D321A, has no inhibitory effect on Maxi K activity. We further found that WNK4 inhibits total and cell surface protein expression of Maxi K equally compared with control groups. A dominant-negative dynamin mutant, K44A, did not alter the WNK4-mediated inhibitory effect on Maxi K surface expression. Treatment with bafilomycin A1 (a proton pump inhibitor) and leupeptin (a lysosomal inhibitor) reversed WNK4 WT-mediated inhibition of Maxi K total protein expression. These findings suggest that WNK4 WT inhibits Maxi K activity by reducing Maxi K protein at the membrane, but that the inhibition is not due to an increase in clathrin-mediated endocytosis of Maxi K, but likely due to enhancing its lysosomal degradation. Also, WNK4's inhibitory effect on Maxi K activity is dependent on its kinase activity.
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Affiliation(s)
- Jieqiu Zhuang
- Department of Nephrology, The Second Affiliated Hospital, Wenzhou Medical College, Zhejiang, China
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30
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Choi SH, Shin TJ, Lee BH, Hwang SH, Lee SM, Lee BC, Park CS, Ha TS, Nah SY. Ginsenoside Rg3 enhances large conductance Ca2+-activated potassium channel currents: a role of Tyr360 residue. Mol Cells 2011; 31:133-40. [PMID: 21191818 PMCID: PMC3932677 DOI: 10.1007/s10059-011-0017-7] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2010] [Revised: 10/25/2010] [Accepted: 11/13/2010] [Indexed: 10/18/2022] Open
Abstract
Ginsenosides, active ingredients of Panax ginseng, are known to exhibit neuroprotective effects. Large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels are key modulators of cellular excitability of neurons and vascular smooth muscle cells. In the present study, we examined the effects of ginsenosides on rat brain BK(Ca) (rSlo) channel activity heterologously expressed in Xenopus oocytes to elucidate the molecular mechanisms how ginsenoside regulates the BK(Ca) channel activity. Ginsenoside Rg(3) (Rg(3)) enhanced outward BK(Ca) channel currents. The Rg(3)-enhancement of outward BK(Ca) channel currents was concentration-dependent, voltage-dependent, and reversible. The EC(50) was 15.1 ± 3.1 μM. Rg(3) actions were not desensitized by repeated treatment. Tetraetylammonium (TEA), a K(+) channel blocker, inhibited BK(Ca) channel currents. We examined whether extracellular TEA treatment could alter the Rg(3) action and vice versa. TEA caused a rightward shift of the Rg(3) concentration-response curve (i.e., much higher concentration of Rg(3) is required for the activation of BK(Ca) channel compared to the absence of TEA), while Rg(3) caused a rightward shift of the TEA concentration-response curve in wild-type channels. Mutation of the extracellular TEA binding site Y360 to Y360I caused a rightward shift of the TEA concentration-response curve and almost abolished both the Rg(3) action and Rg(3)-induced rightward shift of TEA concentration-response curve. These results indicate that Tyr360 residue of BK(Ca) channel plays an important role in the Rg(3)-enhancement of BK(Ca) channel currents.
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Affiliation(s)
- Sun-Hye Choi
- Ginsentology Research Laboratory and Department of Physiology, College of Veterinary Medicine and Bio/Molecular Informatics Center, Konkuk University, Seoul 143-701, Korea
| | - Tae-Joon Shin
- Ginsentology Research Laboratory and Department of Physiology, College of Veterinary Medicine and Bio/Molecular Informatics Center, Konkuk University, Seoul 143-701, Korea
| | - Byung-Hwan Lee
- Ginsentology Research Laboratory and Department of Physiology, College of Veterinary Medicine and Bio/Molecular Informatics Center, Konkuk University, Seoul 143-701, Korea
| | - Sung Hee Hwang
- Ginsentology Research Laboratory and Department of Physiology, College of Veterinary Medicine and Bio/Molecular Informatics Center, Konkuk University, Seoul 143-701, Korea
| | - Sang-Mok Lee
- Ginsentology Research Laboratory and Department of Physiology, College of Veterinary Medicine and Bio/Molecular Informatics Center, Konkuk University, Seoul 143-701, Korea
| | - Byung-Cheol Lee
- Department of Life Science, Gwangju Institute of Science and Technology, Gwangju 500-712, Korea
| | - Cheol-Seung Park
- Department of Life Science, Gwangju Institute of Science and Technology, Gwangju 500-712, Korea
| | - Tal Soo Ha
- Department of Molecular Biology, College of Natural Science, Daegu University, Gyeongsan 712-714, Korea
| | - Seung-Yeol Nah
- Ginsentology Research Laboratory and Department of Physiology, College of Veterinary Medicine and Bio/Molecular Informatics Center, Konkuk University, Seoul 143-701, Korea
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31
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Yang J, Delaloye K, Lee US, Cui J. Patch clamp and perfusion techniques for studying ion channels expressed in Xenopus oocytes. J Vis Exp 2011:2269. [PMID: 21248703 DOI: 10.3791/2269] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022] Open
Abstract
The protocol presented here is designed to study the activation of the large conductance, voltage- and Ca(2+)-activated K(+) (BK) channels. The protocol may also be used to study the structure-function relationship for other ion channels and neurotransmitter receptors. BK channels are widely expressed in different tissues and have been implicated in many physiological functions, including regulation of smooth muscle contraction, frequency tuning of inner hair cells and regulation of neurotransmitter release. BK channels are activated by membrane depolarization and by intracellular Ca(2+) and Mg(2+). Therefore, the protocol is designed to control both the membrane voltage and the intracellular solution. In this protocol, messenger RNA of BK channels is injected into Xenopus laevis oocytes (stage V-VI) followed by 2-5 days of incubation at 18°C. Membrane patches that contain single or multiple BK channels are excised with the inside-out configuration using patch clamp techniques. The intracellular side of the patch is perfused with desired solutions during recording so that the channel activation under different conditions can be examined. To summarize, the mRNA of BK channels is injected into Xenopus laevis oocytes to express channel proteins on the oocyte membrane; patch clamp techniques are used to record currents flowing through the channels under controlled voltage and intracellular solutions.
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Affiliation(s)
- Junqiu Yang
- Department of Energy, Environmental & Chemical Engineering, Washington University, St. Louis, USA
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32
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Ross FA, Rafferty JN, Dallas ML, Ogunbayo O, Ikematsu N, McClafferty H, Tian L, Widmer H, Rowe ICM, Wyatt CN, Shipston MJ, Peers C, Hardie DG, Evans AM. Selective expression in carotid body type I cells of a single splice variant of the large conductance calcium- and voltage-activated potassium channel confers regulation by AMP-activated protein kinase. J Biol Chem 2011; 286:11929-36. [PMID: 21209098 PMCID: PMC3069395 DOI: 10.1074/jbc.m110.189779] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Inhibition of large conductance calcium-activated potassium (BKCa) channels mediates, in part, oxygen sensing by carotid body type I cells. However, BKCa channels remain active in cells that do not serve to monitor oxygen supply. Using a novel, bacterially derived AMP-activated protein kinase (AMPK), we show that AMPK phosphorylates and inhibits BKCa channels in a splice variant-specific manner. Inclusion of the stress-regulated exon within BKCa channel α subunits increased the stoichiometry of phosphorylation by AMPK when compared with channels lacking this exon. Surprisingly, however, the increased phosphorylation conferred by the stress-regulated exon abolished BKCa channel inhibition by AMPK. Point mutation of a single serine (Ser-657) within this exon reduced channel phosphorylation and restored channel inhibition by AMPK. Significantly, RT-PCR showed that rat carotid body type I cells express only the variant of BKCa that lacks the stress-regulated exon, and intracellular dialysis of bacterially expressed AMPK markedly attenuated BKCa currents in these cells. Conditional regulation of BKCa channel splice variants by AMPK may therefore determine the response of carotid body type I cells to hypoxia.
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Affiliation(s)
- Fiona A Ross
- College of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, United Kingdom
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33
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Firth AL, Remillard CV, Platoshyn O, Fantozzi I, Ko EA, Yuan JXJ. Functional ion channels in human pulmonary artery smooth muscle cells: Voltage-dependent cation channels. Pulm Circ 2011; 1:48-71. [PMID: 21927714 PMCID: PMC3173772 DOI: 10.4103/2045-8932.78103] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The activity of voltage-gated ion channels is critical for the maintenance of cellular membrane potential and generation of action potentials. In turn, membrane potential regulates cellular ion homeostasis, triggering the opening and closing of ion channels in the plasma membrane and, thus, enabling ion transport across the membrane. Such transmembrane ion fluxes are important for excitation–contraction coupling in pulmonary artery smooth muscle cells (PASMC). Families of voltage-dependent cation channels known to be present in PASMC include voltage-gated K+ (Kv) channels, voltage-dependent Ca2+-activated K+ (Kca) channels, L- and T- type voltage-dependent Ca2+ channels, voltage-gated Na+ channels and voltage-gated proton channels. When cells are dialyzed with Ca2+-free K+- solutions, depolarization elicits four components of 4-aminopyridine (4-AP)-sensitive Kvcurrents based on the kinetics of current activation and inactivation. In cell-attached membrane patches, depolarization elicits a wide range of single-channel K+ currents, with conductances ranging between 6 and 290 pS. Macroscopic 4-AP-sensitive Kv currents and iberiotoxin-sensitive Kca currents are also observed. Transcripts of (a) two Na+ channel α-subunit genes (SCN5A and SCN6A), (b) six Ca2+ channel α–subunit genes (α1A, α1B, α1X, α1D, α1Eand α1G) and many regulatory subunits (α2δ1, β1-4, and γ6), (c) 22 Kv channel α–subunit genes (Kv1.1 - Kv1.7, Kv1.10, Kv2.1, Kv3.1, Kv3.3, Kv3.4, Kv4.1, Kv4.2, Kv5.1, Kv 6.1-Kv6.3, Kv9.1, Kv9.3, Kv10.1 and Kv11.1) and three Kv channel β-subunit genes (Kvβ1-3) and (d) four Kca channel α–subunit genes (Sloα1 and SK2-SK4) and four Kca channel β-subunit genes (Kcaβ1-4) have been detected in PASMC. Tetrodotoxin-sensitive and rapidly inactivating Na+ currents have been recorded with properties similar to those in cardiac myocytes. In the presence of 20 mM external Ca2+, membrane depolarization from a holding potential of -100 mV elicits a rapidly inactivating T-type Ca2+ current, while depolarization from a holding potential of -70 mV elicits a slowly inactivating dihydropyridine-sensitive L-type Ca2+ current. This review will focus on describing the electrophysiological properties and molecular identities of these voltage-dependent cation channels in PASMC and their contribution to the regulation of pulmonary vascular function and its potential role in the pathogenesis of pulmonary vascular disease.
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Affiliation(s)
- Amy L Firth
- The Salk Institute for Biological Studies, La Jolla, California, USA
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34
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Pantazis A, Kohanteb AP, Olcese R. Relative motion of transmembrane segments S0 and S4 during voltage sensor activation in the human BK(Ca) channel. J Gen Physiol 2010; 136:645-57. [PMID: 21078868 PMCID: PMC2995153 DOI: 10.1085/jgp.201010503] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2010] [Accepted: 11/01/2010] [Indexed: 01/06/2023] Open
Abstract
Large-conductance voltage- and Ca(2+)-activated K(+) (BK(Ca)) channel α subunits possess a unique transmembrane helix referred to as S0 at their N terminus, which is absent in other members of the voltage-gated channel superfamily. Recently, S0 was found to pack close to transmembrane segments S3 and S4, which are important components of the BK(Ca) voltage-sensing apparatus. To assess the role of S0 in voltage sensitivity, we optically tracked protein conformational rearrangements from its extracellular flank by site-specific labeling with an environment-sensitive fluorophore, tetramethylrhodamine maleimide (TMRM). The structural transitions resolved from the S0 region exhibited voltage dependence similar to that of charge-bearing transmembrane domains S2 and S4. The molecular determinant of the fluorescence changes was identified in W203 at the extracellular tip of S4: at hyperpolarized potential, W203 quenches the fluorescence of TMRM labeling positions at the N-terminal flank of S0. We provide evidence that upon depolarization, W203 (in S4) moves away from the extracellular region of S0, lifting its quenching effect on TMRM fluorescence. We suggest that S0 acts as a pivot component against which the voltage-sensitive S4 moves upon depolarization to facilitate channel activation.
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Affiliation(s)
- Antonios Pantazis
- Department of Anesthesiology, Division of Molecular Medicine, Brain Research Institute, and Cardiovascular Research Laboratories, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90075
| | - Azadeh P. Kohanteb
- Department of Anesthesiology, Division of Molecular Medicine, Brain Research Institute, and Cardiovascular Research Laboratories, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90075
| | - Riccardo Olcese
- Department of Anesthesiology, Division of Molecular Medicine, Brain Research Institute, and Cardiovascular Research Laboratories, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90075
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Latorre R, Morera FJ, Zaelzer C. Allosteric interactions and the modular nature of the voltage- and Ca2+-activated (BK) channel. J Physiol 2010; 588:3141-8. [PMID: 20603335 DOI: 10.1113/jphysiol.2010.191999] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
The high conductance voltage- and Ca(2+)-activated K(+) channel is one of the most broadly expressed channels in mammals. This channel is named BK for 'big K' because of its single-channel conductance that can be as large as 250 pS in 100 mm symmetrical K(+). BK channels increase their activity by membrane depolarization or an increase in cytosolic Ca(2+). One of the key features that defines the behaviour of BK channels is that neither Ca(2+) nor voltage is strictly necessary for channel activation. This and several other observations led to the idea that both Ca(2+) and voltage increase the open probability by an allosteric mechanism. In this type of mechanism, the processes of voltage sensor displacement, Ca(2+) binding and pore opening are independent equilibria that interact allosterically with each other. These allosteric interactions in BK channels reside in the structural characteristics of the BK channel in the sense that voltage and Ca(2+) sensors and the pore need to be contained in different structures or 'modules'. Through electrophysiological, mutagenesis, biochemical and fluorescence studies these modules have been identified and, more important, some of the interactions between them have been unveiled. In this review, we have covered the main advances achieved during the last few years in the elucidation of the structure of the BK channel and how this is related with its function as an allosteric protein.
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Affiliation(s)
- Ramon Latorre
- Universidad de Valparaiso, Centro de Neurociencia, Gran Bretana 1111, Playa Ancha, Valparaiso, V 2340000, Chile.
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Zhang XL, Mok LP, Katz EJ, Gold MS. BKCa currents are enriched in a subpopulation of adult rat cutaneous nociceptive dorsal root ganglion neurons. Eur J Neurosci 2010; 31:450-62. [PMID: 20105244 DOI: 10.1111/j.1460-9568.2009.07060.x] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
The biophysical properties and distribution of voltage-dependent, Ca(2+) -modulated K(+) (BK(Ca)) currents among subpopulations of acutely dissociated DiI-labeled cutaneous sensory neurons from the adult rat were characterized with whole-cell patch-clamp techniques. BK(Ca) currents were isolated from total K(+) current with iberiotoxin, charybdotoxin or paxilline. There was considerable variability in biophysical properties of BK(Ca) currents. There was also variability in the distribution of BK(Ca) current among subpopulations of cutaneous dorsal root ganglia (DRG) neurons. While present in each of the subpopulations defined by cell body size, IB4 binding or capsaicin sensitivity, BK(Ca) current was present in the vast majority (> 90%) of small-diameter IB4+ neurons, but was present in only a minority of neurons in subpopulations defined by other criteria (i.e. small-diameter IB4-). Current-clamp analysis indicated that in IB4+ neurons, BK(Ca) currents contribute to the repolarization of the action potential and adaptation in response to sustained membrane depolarization, while playing little role in the determination of action potential threshold. Reverse transcriptase-polymerase chain reaction analysis of mRNA collected from whole DRG revealed the presence of multiple splice variants of the BK(Ca) channel alpha-subunit, rslo and all four of the accessory beta-subunits, suggesting that heterogeneity in the biophysical and pharmacological properties of BK(Ca) current in cutaneous neurons reflects, at least in part, the differential distribution of splice variants and/or beta-subunits. Because even a small decrease in BK(Ca) current appears to have a dramatic influence on excitability, modulation of this current may contribute to sensitization of nociceptive afferents observed following tissue injury.
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Affiliation(s)
- Xiu-Lin Zhang
- Department of Biomedical Sciences, Dental School, University of Maryland, Baltimore, MD 21201, USA
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Rosenfeld CR, Word RA, DeSpain K, Liu XT. Large conductance Ca2+-activated K+ channels contribute to vascular function in nonpregnant human uterine arteries. Reprod Sci 2009; 15:651-60. [PMID: 18836130 DOI: 10.1177/1933719108319160] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Large conductance K( +) channels (BK(Ca)) are expressed in uterine artery (UA) smooth muscle from nonpregnant and pregnant sheep and contribute to the regulation of basal vascular tone and responses to estrogen and vasoconstrictors. To determine if BK(Ca) are expressed in women and contribute to UA function, we collected UA from nonpregnant women (n = 31) at elective hysterectomy and analyzed for subunit protein, localization with immunohistochemistry, and function using endothelium-denuded rings. UA expresses BK(Ca) alpha -, beta1- and beta2-subunit protein. KCl and phenylephrine (PE, an alpha(1)-agonist) caused dose-dependent vasoconstriction (P < .001), and UA precontracted with PE dose-dependently relaxed with sodium nitroprusside (SNP; P < .001).Tetraethylammonium chloride (TEA, 0.2-1.0 mM), a BK(Ca) inhibitor, dose-dependently increased resting tone (P = .004; 28% +/- 5.3% with 1.0 mM), enhanced PE-induced (10(-)(6) M) vasoconstriction (P < .04), and attenuated SNP-induced relaxation at 1.0 mM (P = .02). BK( Ca) are expressed in human UA and modulate vascular function by attenuating vasoconstrictor responses and contributing to nitric oxide-induced vasorelaxation.
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Affiliation(s)
- Charles R Rosenfeld
- Division of Neonatal-Perinatal Medicine, Department of Pediatrics, University of Texas Southwestern Medical Center at Dallas, TX 75390, USA.
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Lee JH, Kim HJ, Kim HD, Lee BC, Chun JS, Park CS. Modulation of the conductance-voltage relationship of the BK(Ca) channel by shortening the cytosolic loop connecting two RCK domains. Biophys J 2009; 97:730-7. [PMID: 19651031 DOI: 10.1016/j.bpj.2009.04.058] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2008] [Revised: 04/20/2009] [Accepted: 04/24/2009] [Indexed: 12/25/2022] Open
Abstract
Calcium-dependent gating of large-conductance calcium-activated potassium (BK(Ca)) channels is mediated by the intracellular carboxyl terminus, which contains two domains of regulator of K(+) conductance (RCK). In mammalian BK(Ca) channels, the two RCK domains are separated by a protein segment of 101 residues that is poorly conserved in evolution and predicted to have no regular secondary structures. We investigated the functional importance of this loop using a series of deletion mutations. We found that the length, rather than the specific sequence at the central region of the segment, is critical for the functionality of the channel. As the length of the loop is progressively shorted, the conductance-voltage relationship gradually shifts toward more positive voltages with a minimum length of 70 amino acids, in an apparent response to increased tension within the loop. Thus, the functional activity of the BK(Ca) channel can be modulated by altering the tension of this loop region.
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Affiliation(s)
- Ju-Ho Lee
- Department of Life Science, Gwangju Institute of Science and Technology, Gwangju, Korea
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Zhu S, Browning DD, White RE, Fulton D, Barman SA. Mutation of protein kinase C phosphorylation site S1076 on alpha-subunits affects BK(Ca) channel activity in HEK-293 cells. Am J Physiol Lung Cell Mol Physiol 2009; 297:L758-66. [PMID: 19592459 DOI: 10.1152/ajplung.90518.2008] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Large conductance, calcium- and voltage-activated potassium (BK(Ca)) channels are important modulators of pulmonary vascular smooth muscle membrane potential, and phosphorylation of BK(Ca) channels by protein kinases regulates pulmonary arterial smooth muscle function. However, little is known about the effect of phosphorylating specific channel subunits on BK(Ca) channel activity. The present study was done to determine the effect of mutating protein kinase C (PKC) phosphorylation site serine 1076 (S1076) on transfected human BK(Ca) channel alpha-subunits in human embryonic kidney (HEK-293) cells, a heterologous expression system devoid of endogenous BK(Ca) channels. Results showed that mutating S1076 altered the effect of PKC activation on BK(Ca) channels in HEK-293 cells. Specifically, the phospho-deficient mutation BK(Ca)-alpha(S1076A)/beta(1) attenuated the excitatory effect of the PKC activator phorbol myristate acetate (PMA) on BK(Ca) channels, whereas the phospho-mimetic mutation BK(Ca)-alpha(S1076E)/beta(1) increased the excitatory effect of PMA on BK(Ca) channels. In addition, the phospho-null mutation S1076A blocked the activating effect of cGMP-dependent protein kinase G (PKG) on BK(Ca) channels. Collectively, these results suggest that specific putative PKC phosphorylation site(s) on human BK(Ca) channel alpha-subunits influences BK(Ca) channel activity, which may subsequently alter pulmonary vascular smooth muscle function and tone.
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Affiliation(s)
- Shu Zhu
- Dept. of Pharmacology and Toxicology, Medical College of Georgia, Augusta, GA 30912, USA
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Stadnicka A, Contney SJ, Moreno C, Weihrauch D, Bosnjak ZJ, Roman RJ, Stekiel TA. Mechanism of differential cardiovascular response to propofol in Dahl salt-sensitive, Brown Norway, and chromosome 13-substituted consomic rat strains: role of large conductance Ca2+ and voltage-activated potassium channels. J Pharmacol Exp Ther 2009; 330:727-35. [PMID: 19541907 DOI: 10.1124/jpet.109.154104] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Cardiovascular sensitivity to general anesthetics is highly variable among individuals in both human and animal models, but little is known about the genetic determinants of drug response to anesthetics. Recently, we reported that propofol (2,6-diisopropylphenol) causes circulatory instability in Dahl salt-sensitive SS/JRHsdMcwi (SS) rats but not in Brown Norway BN/NHsdMcwi (BN) rats and that these effects are related to genes on chromosome 13. Based on the hypothesis that propofol does target mesenteric circulation, we investigated propofol modulation of mesenteric arterial smooth muscle cells (MASMC) in SS and BN rats. The role of chromosome 13 was tested using SS-13(BN)/Mcwi and BN-13(SS)/Mcwi consomic strains with chromosome 13 substitution. Propofol (5 microM) produced a greater in situ hyperpolarization of MASMC membrane potential in SS than BN rats, and this effect was abrogated by iberiotoxin, a voltage-activated potassium (BK) channel blocker. In inside-out patches, the BK channel number, P(o), and apparent Ca(2+) sensitivity, and propofol sensitivity all were significantly greater in MASMC of SS rats. The density of whole-cell BK current was increased by propofol more in SS than BN myocytes. Immunolabeling confirmed higher expression of BK alpha subunit in MASMC of SS rats. Furthermore, the hyperpolarization produced by propofol, the BK channel properties, and propofol sensitivity were modified in MASMC of SS-13(BN)/Mcwi and BN-13(SS)/Mcwi strains toward the values observed in the background SS and BN strains. We conclude that differential function and expression of BK channels, resulting from genetic variation within chromosome 13, contribute to the enhanced propofol sensitivity in SS and BN-13(SS)/Mcwi versus BN and SS-13(BN)/Mcwi strains.
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Affiliation(s)
- Anna Stadnicka
- Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, Wisconsin 53226, USA.
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Gao L, Cong B, Zhang L, Ni X. Expression of the calcium-activated potassium channel in upper and lower segment human myometrium during pregnancy and parturition. Reprod Biol Endocrinol 2009; 7:27. [PMID: 19344525 PMCID: PMC2670306 DOI: 10.1186/1477-7827-7-27] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/13/2009] [Accepted: 04/05/2009] [Indexed: 11/30/2022] Open
Abstract
BACKGROUND Large conductance calcium-activated potassium channel (BKCa) plays an important role in the control of uterine contractility during pregnancy. The change from uterine quiescence to enhanced contractile activity may be associated with the spatial and temporal expression of BKCa within myometrium. The objectives of this study were to examine the expression of BKCa alpha- and beta-subunit in upper segment (US) and lower segment (LS) regions of uterus, and to investigate for the possibly differential expression of these proteins in US and LS myometrium obtained from three functional states: (1) non-pregnant (NP); (2) term pregnant not in labour (TNL) and (3) term pregnant in labour (TL). METHODS Myometrial biopsies were collected from non-pregnant women at hysterectomy and pregnant women at either elective caesarean section or emergency caesarean section. Protein expression level and cellular localization of BKCa alpha- and beta-subunit in US and LS myometrium were determined by Western blot analysis and immunohistochemistry, respectively. RESULTS BKCa alpha- and beta-subunit were predominantly localized to myometrial smooth muscle in both US and LS myometrium obtained from non-pregnant and pregnant patients. The level of BKCa alpha-subunit in US but not in LS was significantly higher in NP myometrium than those measured in myometrium obtained during pregnancy. Lower expression of BKCa alpha-subunit in both US and LS was found in TL than in TNL biopsies. Expression of beta-subunit in both US and LS myometrium was significantly reduced in TL group compared with those measured in TNL group. There was no significant difference in BKCa beta-subunit expression in either US or LS between NP and TNL group. CONCLUSION Our results suggest that expression of BKCa alpha- and beta-subunit in pregnant myometrium is reduced during labour, which is consistent with the myometrial activity at the onset of parturition.
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Affiliation(s)
- Lu Gao
- Department of Physiology, Second Military Medical University, Shanghai 200433, PR China.
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Abstract
Large conductance, Ca(2+)-activated potassium (BK) channels are widely expressed throughout the animal kingdom and play important roles in many physiological processes, such as muscle contraction, neural transmission and hearing. These physiological roles derive from the ability of BK channels to be synergistically activated by membrane voltage, intracellular Ca(2+) and other ligands. Similar to voltage-gated K(+) channels, BK channels possess a pore-gate domain (S5-S6 transmembrane segments) and a voltage-sensor domain (S1-S4). In addition, BK channels contain a large cytoplasmic C-terminal domain that serves as the primary ligand sensor. The voltage sensor and the ligand sensor allosterically control K(+) flux through the pore-gate domain in response to various stimuli, thereby linking cellular metabolism and membrane excitability. This review summarizes the current understanding of these structural domains and their mutual interactions in voltage-, Ca(2+)- and Mg(2+)-dependent activation of the channel.
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Affiliation(s)
- J Cui
- Department of Biomedical Engineering and Cardiac Bioelectricity and Arrhythmia Center, Washington University, 1 Brookings Drive, St. Louis, Missouri 63130, USA.
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Yang H, Shi J, Zhang G, Yang J, Delaloye K, Cui J. Activation of Slo1 BK channels by Mg2+ coordinated between the voltage sensor and RCK1 domains. Nat Struct Mol Biol 2008; 15:1152-9. [PMID: 18931675 PMCID: PMC2579968 DOI: 10.1038/nsmb.1507] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2008] [Accepted: 09/29/2008] [Indexed: 11/29/2022]
Abstract
The voltage sensor domain (VSD) and the ligand sensor (cytoplasmic domain) of BK channels synergistically control channel activities, thereby integrating electrical and chemical signals for cell function. Studies show that intracellular Mg2+ mediates the interaction between these sensory domains to activate the channel through an electrostatic interaction with the VSD. Here we report that Mg2+ binds to a site that consists of amino acid side-chains from both the VSD (Asp99 and Asn172) and the cytoplasmic domain (Glu374 and Glu399). For each Mg2+ binding site the residues in the VSD and those in the cytoplasmic domain come from neighboring subunits. These results suggest that the VSD and the cytoplasmic domains from different subunits may interact during channel gating, and the packing of VSD or the RCK1 domain to the pore in BK channels differ from that in Kv1.2 or MthK channels.
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Affiliation(s)
- Huanghe Yang
- Department of Biomedical Engineering, and Cardiac Bioelectricity and Arrhythmia Center, Washington University, 1 Brookings Drive, St. Louis, Missouri 63130, USA
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Zhou XB, Wulfsen I, Lutz S, Utku E, Sausbier U, Ruth P, Wieland T, Korth M. M2 muscarinic receptors induce airway smooth muscle activation via a dual, Gbetagamma-mediated inhibition of large conductance Ca2+-activated K+ channel activity. J Biol Chem 2008; 283:21036-44. [PMID: 18524769 PMCID: PMC3258941 DOI: 10.1074/jbc.m800447200] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2008] [Revised: 04/24/2008] [Indexed: 11/06/2022] Open
Abstract
Airway smooth muscle is richly endowed with muscarinic receptors of the M(2) and M(3) subtype. Stimulation of these receptors inhibits large conductance calcium-activated K(+) (BK) channels, a negative feed back regulator, in a pertussis toxin-sensitive manner and thus facilitates contraction. The underlying mechanism, however, is unknown. We therefore studied the activity of bovine trachea BK channels in HEK293 cells expressing the M(2) or M(3) receptor (M(2)R or M(3)R). In M(2)R- but not M(3)R-expressing cells, maximal effective concentrations of carbamoylcholine (CCh) inhibited whole cell BK currents by 53%. This M(2)R-induced inhibition was abolished by pertussis toxin treatment or overexpression of the Gbetagamma scavenger transducin-alpha. In inside-out patches, direct application of 300 nm purified Gbetagamma decreased channel open probability by 55%. The physical interaction of Gbetagamma with BK channels was confirmed by co-immunoprecipitation. Interestingly, inhibition of phospholipase C as well as protein kinase C activities also reversed the CCh effect but to a smaller (approximately 20%) extent. Mouse tracheal cells responded similarly to CCh, purified Gbetagamma and phospholipase C/protein kinase C inhibition as M(2)R-expressing HEK293 cells. Our results demonstrate that airway M(2)Rs inhibit BK channels by a dual, Gbetagamma-mediated mechanism, a direct membrane-delimited interaction, and the activation of the phospholipase C/protein kinase C pathway.
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Affiliation(s)
- Xiao-Bo Zhou
- Institut für Pharmakologie für
Pharmazeuten, Universitätsklinikum Hamburg-Eppendorf, 20246 Hamburg,
Germany, the Pharmakologie und Toxikologie,
Pharmazeutisches Institut, Universität Tübingen, 72076
Tübingen, Germany, and the Institut
für Experimentelle und Klinische Pharmakologie und Toxikologie,
Medizinische Fakultät Mannheim, Universität Heidelberg, 68169
Mannheim, Germany
| | - Iris Wulfsen
- Institut für Pharmakologie für
Pharmazeuten, Universitätsklinikum Hamburg-Eppendorf, 20246 Hamburg,
Germany, the Pharmakologie und Toxikologie,
Pharmazeutisches Institut, Universität Tübingen, 72076
Tübingen, Germany, and the Institut
für Experimentelle und Klinische Pharmakologie und Toxikologie,
Medizinische Fakultät Mannheim, Universität Heidelberg, 68169
Mannheim, Germany
| | - Susanne Lutz
- Institut für Pharmakologie für
Pharmazeuten, Universitätsklinikum Hamburg-Eppendorf, 20246 Hamburg,
Germany, the Pharmakologie und Toxikologie,
Pharmazeutisches Institut, Universität Tübingen, 72076
Tübingen, Germany, and the Institut
für Experimentelle und Klinische Pharmakologie und Toxikologie,
Medizinische Fakultät Mannheim, Universität Heidelberg, 68169
Mannheim, Germany
| | - Emine Utku
- Institut für Pharmakologie für
Pharmazeuten, Universitätsklinikum Hamburg-Eppendorf, 20246 Hamburg,
Germany, the Pharmakologie und Toxikologie,
Pharmazeutisches Institut, Universität Tübingen, 72076
Tübingen, Germany, and the Institut
für Experimentelle und Klinische Pharmakologie und Toxikologie,
Medizinische Fakultät Mannheim, Universität Heidelberg, 68169
Mannheim, Germany
| | - Ulrike Sausbier
- Institut für Pharmakologie für
Pharmazeuten, Universitätsklinikum Hamburg-Eppendorf, 20246 Hamburg,
Germany, the Pharmakologie und Toxikologie,
Pharmazeutisches Institut, Universität Tübingen, 72076
Tübingen, Germany, and the Institut
für Experimentelle und Klinische Pharmakologie und Toxikologie,
Medizinische Fakultät Mannheim, Universität Heidelberg, 68169
Mannheim, Germany
| | - Peter Ruth
- Institut für Pharmakologie für
Pharmazeuten, Universitätsklinikum Hamburg-Eppendorf, 20246 Hamburg,
Germany, the Pharmakologie und Toxikologie,
Pharmazeutisches Institut, Universität Tübingen, 72076
Tübingen, Germany, and the Institut
für Experimentelle und Klinische Pharmakologie und Toxikologie,
Medizinische Fakultät Mannheim, Universität Heidelberg, 68169
Mannheim, Germany
| | - Thomas Wieland
- Institut für Pharmakologie für
Pharmazeuten, Universitätsklinikum Hamburg-Eppendorf, 20246 Hamburg,
Germany, the Pharmakologie und Toxikologie,
Pharmazeutisches Institut, Universität Tübingen, 72076
Tübingen, Germany, and the Institut
für Experimentelle und Klinische Pharmakologie und Toxikologie,
Medizinische Fakultät Mannheim, Universität Heidelberg, 68169
Mannheim, Germany
| | - Michael Korth
- Institut für Pharmakologie für
Pharmazeuten, Universitätsklinikum Hamburg-Eppendorf, 20246 Hamburg,
Germany, the Pharmakologie und Toxikologie,
Pharmazeutisches Institut, Universität Tübingen, 72076
Tübingen, Germany, and the Institut
für Experimentelle und Klinische Pharmakologie und Toxikologie,
Medizinische Fakultät Mannheim, Universität Heidelberg, 68169
Mannheim, Germany
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Subunit-specific effect of the voltage sensor domain on Ca2+ sensitivity of BK channels. Biophys J 2008; 94:4678-87. [PMID: 18339745 DOI: 10.1529/biophysj.107.121590] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Large conductance Ca(2+)- and voltage-activated K(+) (BK) channels, composed of pore-forming alpha-subunits and auxiliary beta-subunits, play important roles in diverse physiological processes. The differences in BK channel phenotypes are primarily due to the tissue-specific expression of beta-subunits (beta1-beta4) that modulate channel function differently. Yet, the molecular basis of the subunit-specific regulation is not clear. In our study, we demonstrate that perturbation of the voltage sensor in BK channels by mutations selectively disrupts the ability of the beta1-subunit--but not that of the beta2-subunit--to enhance apparent Ca(2+) sensitivity. These mutations change the number of equivalent gating charges, the voltage dependence of voltage sensor movements, the open-close equilibrium of the channel, and the allosteric coupling between voltage sensor movements and channel opening to various degrees, indicating that they alter the conformation and movements of the voltage sensor and the activation gate. Similarly, the ability of the beta1-subunit to enhance apparent Ca(2+) sensitivity is diminished to various degrees, correlating quantitatively with the shift of voltage dependence of voltage sensor movements. In contrast, none of these mutations significantly reduces the ability of the beta2-subunit to enhance Ca(2+) sensitivity. These results suggest that the beta1-subunit enhances Ca(2+) sensitivity by altering the conformation and movements of the voltage sensor, whereas the similar function of the beta2-subunit is governed by a distinct mechanism.
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Burrell BD, Crisp KM. Serotonergic Modulation of Afterhyperpolarization in a Neuron That Contributes to Learning in the Leech. J Neurophysiol 2008; 99:605-16. [DOI: 10.1152/jn.00989.2007] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Modulation of afterhyperpolarization (AHP) represents an important mechanism by which excitability of a neuron can be regulated. In the leech brain, sensitization enhances excitability of the S-cell, an interneuron thought to play an important role in this form of nonassociative learning. This increase in excitability is serotonin (5-HT) dependent, but it is not known whether changes in AHP contribute to 5-HT–mediated enhancement of excitability. Therefore electrophysiological recordings and computational modeling were used to determine whether 5-HT enhances excitability via modulation of AHP. 5-HT reduced S-cell AHP and this decrease in the AHP corresponded with an increase in excitability. Little or no AHP is observed in the presence of Ca2+-free saline, suggesting the involvement of Ca2+-dependent K+channels. Furthermore, AHP amplitude decreased following treatment with drugs (tubocurare and charybdotoxin) that block Ca2+-dependent K+channel activity. The S-cell also exhibits an afterdepolarization (ADP), which is usually masked by the AHP, and was inhibited by the Na+channel blocker saxitoxin. A model of the S-cell AHP was constructed using two Ca2+-dependent K+currents and a Na+-driven ADP current. Reduction of the model conductances underlying the AHP to mimic the effects of 5-HT was sufficient to enhance excitability. These findings were confirmed in occlusion experiments in which pretreatment with tubocurare was able to block 5-HT–mediated decreases in mAHP levels and increases in excitability. These data show that modulation of S-cell AHP can contribute to 5-HT–mediated increases in excitability and that the S-cell afterpotential is due to the combined effects of AHP- and ADP-producing currents.
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Wu X, Yang Y, Gui P, Sohma Y, Meininger GA, Davis GE, Braun AP, Davis MJ. Potentiation of large conductance, Ca2+-activated K+ (BK) channels by alpha5beta1 integrin activation in arteriolar smooth muscle. J Physiol 2008; 586:1699-713. [PMID: 18218680 DOI: 10.1113/jphysiol.2007.149500] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Injury/degradation of the extracellular matrix (ECM) is associated with vascular wall remodelling and impaired reactivity, a process in which altered ECM-integrin interactions play key roles. Previously, we found that peptides containing the RGD integrin-binding sequence produce sustained vasodilatation of rat skeletal muscle arterioles. Here, we tested the hypothesis that RGD ligands work through alpha5beta1 integrin to modulate the activity of large conductance, Ca(2+)-activated K(+) (BK) channels in arteriolar smooth muscle. K(+) currents were recorded in single arteriolar myocytes using whole-cell and single-channel patch clamp methods. Activation of alpha5beta1 integrin by an appropriate, insoluble alpha5beta1 antibody resulted in a 30-50% increase in the amplitude of iberiotoxin (IBTX)-sensitive, whole-cell K(+) current. Current potentiation occurred 1-8 min after bead-antibody application to the cell surface. Similarly, the endogenous alpha5beta1 integrin ligand fibronectin (FN) potentiated IBTX-sensitive K(+) current by 26%. Current potentiation was blocked by the c-Src inhibitor PP2 but not by PP3 (0.1-1 mum). In cell-attached patches, number of open channels x open probability (NP(o)) of a 230-250 pS K(+) channel was significantly increased after FN application locally to the external surface of cell-attached patches through the recording pipette. In excised, inside-out patches, the same method of FN application led to large, significant increases in NP(o) and caused a leftward shift in the NP(o)-voltage relationship at constant [Ca(2+)]. PP2 (but not PP3) nearly abolished the effect of FN on channel activity, suggesting that signalling between the integrin and channel involved an increase in Ca(2+)sensitivity of the channel via a membrane-delimited pathway. The effects of alpha5beta1 integrin activation on both whole-cell and single-channel BK currents could be reproduced in HEK 293 cells expressing the BK channel alpha-subunit. This is the first demonstration at the single-channel level that integrin signalling can regulate an ion channel. Our results show that alpha5beta1 integrin activation potentiates BK channel activity in vascular smooth muscle through both Ca(2+)- and c-Src-dependent mechanisms. This mechanism is likely to play a role in the arteriolar dilatation and impaired vascular reactivity associated with ECM degradation.
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Affiliation(s)
- Xin Wu
- Department of Medical Pharmacology & Physiology, University of Missouri School of Medicine, 1 Hospital Dr, Rm M451, Columbia, MO 65212, USA.
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Potassium channels in the regulation of pulmonary artery smooth muscle cell proliferation and apoptosis: pharmacotherapeutic implications. Br J Pharmacol 2007; 153 Suppl 1:S99-S111. [PMID: 18084317 DOI: 10.1038/sj.bjp.0707635] [Citation(s) in RCA: 100] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Maintaining the proper balance between cell apoptosis and proliferation is required for normal tissue homeostasis; when this balance is disrupted, disease such as pulmonary arterial hypertension (PAH) can result. Activity of K(+) channels plays a major role in regulating the pulmonary artery smooth muscle cell (PASMC) population in the pulmonary vasculature, as they are involved in cell apoptosis, survival and proliferation. PASMCs from PAH patients demonstrate many cellular abnormalities linked to K(+) channels, including decreased K(+) current, downregulated expression of various K(+) channels, and inhibited apoptosis. K(+) is the major intracellular cation, and the K(+) current is a major determinant of cell volume. Apoptotic volume decrease (AVD), an early hallmark and prerequisite of programmed cell death, is characterized by K(+) and Cl(-) efflux. In addition to its role in AVD, cytosolic K(+) can be inhibitory toward endogenous caspases and nucleases and can suppress mitochondrial cytochrome c release. In PASMC, K(+) channel activation accelerates AVD and enhances apoptosis, while K(+) channel inhibition decelerates AVD and inhibits apoptosis. Finally, inhibition of K(+) channels, by increasing cytosolic [Ca(2+)] as a result of membrane depolarization-mediated opening of voltage-dependent Ca(2+) channels, leads to PASMC contraction and proliferation. The goals of this review are twofold: (1) to elucidate the role of K(+) ions and K(+) channels in the proliferation and apoptosis of PASMC, with an emphasis on abnormal cell growth in human and animal models of PAH, and (2) to elaborate upon the targeting of K(+) flux pathways for pharmacological treatment of pulmonary vascular disease.
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Vascular large conductance calcium-activated potassium channels: functional role and therapeutic potential. Naunyn Schmiedebergs Arch Pharmacol 2007; 376:145-55. [PMID: 17932654 DOI: 10.1007/s00210-007-0193-3] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2007] [Accepted: 09/19/2007] [Indexed: 12/22/2022]
Abstract
Large-conductance Ca2+-activated K+ channels (BK Ca or maxiK channels) are expressed in different cell types. They play an essential role in the regulation of various cell functions. In particular, BK Ca channels have been extensively studied in vascular smooth muscle cells, where they contribute to the control of vascular tone. They facilitate the feedback regulation against the rise of intracellular Ca2+, membrane depolarization and vasoconstriction. BK Ca channels promote a K+ outward current and lead to membrane hyperpolarization. In endothelial cells expression and function of BK Ca channels play an important role in the regulation of the vascular smooth muscle activity. Endothelial BK Ca channels modulate the biosyntheses and release of various vasoactive modulators and regulate the membrane potential. Because of their regulatory role in vascular tone, endothelial BK Ca channels have been suggested as therapeutic targets for the treatment of cardiovascular diseases. Hypertension, atherosclerosis, and diabetes are associated with altered current amplitude, open probability, and Ca2+-sensing of BK Ca channels. The properties of BK Ca channels and their role in endothelial and vascular smooth muscle cells would address them as potential therapeutic targets. Further studies are necessary to identify the detailed molecular mechanisms of action and to investigate selective BK Ca channels openers as possible therapeutic agents for clinical use.
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Ko EA, Burg ED, Platoshyn O, Msefya J, Firth AL, Yuan JXJ. Functional characterization of voltage-gated K+ channels in mouse pulmonary artery smooth muscle cells. Am J Physiol Cell Physiol 2007; 293:C928-37. [PMID: 17581857 DOI: 10.1152/ajpcell.00101.2007] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Mice are useful animal models to study pathogenic mechanisms involved in pulmonary vascular disease. Altered expression and function of voltage-gated K(+) (K(V)) channels in pulmonary artery smooth muscle cells (PASMCs) have been implicated in the development of pulmonary arterial hypertension. K(V) currents (I(K(V))) in mouse PASMCs have not been comprehensively characterized. The main focus of this study was to determine the biophysical and pharmacological properties of I(K(V)) in freshly dissociated mouse PASMCs with the patch-clamp technique. Three distinct whole cell I(K(V)) were identified based on the kinetics of activation and inactivation: rapidly activating and noninactivating currents (in 58% of the cells tested), rapidly activating and slowly inactivating currents (23%), and slowly activating and noninactivating currents (17%). Of the cells that demonstrated the rapidly activating noninactivating current, 69% showed I(K(V)) inhibition with 4-aminopyridine (4-AP), while 31% were unaffected. Whole cell I(K(V)) were very sensitive to tetraethylammonium (TEA), as 1 mM TEA decreased the current amplitude by 32% while it took 10 mM 4-AP to decrease I(K(V)) by a similar amount (37%). Contribution of Ca(2+)-activated K(+) (K(Ca)) channels to whole cell I(K(V)) was minimal, as neither pharmacological inhibition with charybdotoxin or iberiotoxin nor perfusion with Ca(2+)-free solution had an effect on the whole cell I(K(V)). Steady-state activation and inactivation curves revealed a window K(+) current between -40 and -10 mV with a peak at -31.5 mV. Single-channel recordings revealed large-, intermediate-, and small-amplitude currents, with an averaged slope conductance of 119.4 +/- 2.7, 79.8 +/- 2.8, 46.0 +/- 2.2, and 23.6 +/- 0.6 pS, respectively. These studies provide detailed electrophysiological and pharmacological profiles of the native K(V) currents in mouse PASMCs.
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Affiliation(s)
- Eun A Ko
- Div. of Pulmonary and Critical Care Medicine, Dept. of Medicine, Univ. of California, San Diego, 9500 Gilman Dr., MC 0725, La Jolla, CA 92093-0725, USA
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