1
|
Kshatri A, Rivero-Pérez B, Giraldez T. Subunit-specific inhibition of BK channels by piperine. Biophys J 2024; 123:1942-1953. [PMID: 37700524 PMCID: PMC11309970 DOI: 10.1016/j.bpj.2023.09.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2023] [Revised: 08/03/2023] [Accepted: 09/08/2023] [Indexed: 09/14/2023] Open
Abstract
Piperine is the principal alkaloid present in black pepper and is well-known for its diverse pharmacological effects, including inhibition of different ion channels. Large conductance Ca2+-activated K+ channels (BK) are widely expressed across several tissues and play a vital role in many physiological functions. In this study, we investigated the pharmacological effects of piperine on various BK channel subunit compositions (BKα, BKαβ1,4, BKαγ1,3) expressed in HEK293T cells. Piperine in zero Ca2+ reversibly inhibited currents from the pore-forming BKα channels in a dose-dependent manner with a half-maximal inhibitory concentration (IC50) of 4.8 μM. Elevating the internal Ca2+ concentration from 0 to 100 μM significantly attenuated the inhibitory effects of piperine on BKα channels. The mutation G311S in the pore domain failed to alter the modulatory effects of piperine, whereas deletion of the entire cytoplasmic domain from BKα channels ablated its inhibitory effects. Addition of either BKβ1 or β4 regulatory subunits did not alter the efficacy of piperine on BKα channels. Interestingly, co-expression of either BKγ1 or BKγ3 subunits greatly diminished the ability of piperine to inhibit BKα channels. Our findings demonstrate that piperine is a potent natural modulator of BKα/BKαβ1,4 subunits but not BKαγ1,3 subunits. The mechanism of piperine modulation appeared to be allosteric and differs from that of other BK pore blockers (paxilline, peptide toxins, and quaternary ammonium compounds). Together, our results unravel the potential of piperine to inhibit BK channels, providing a new tool to explore mechanisms underlying the effects of regulatory subunits.
Collapse
Affiliation(s)
- Aravind Kshatri
- Department of Basic Medical Sciences, Medical School, Universidad de La Laguna, Tenerife, Spain; Instituto de Tecnologias Biomedicas, Universidad de La Laguna, Tenerife, Spain
| | - Belinda Rivero-Pérez
- Department of Basic Medical Sciences, Medical School, Universidad de La Laguna, Tenerife, Spain; Instituto de Tecnologias Biomedicas, Universidad de La Laguna, Tenerife, Spain
| | - Teresa Giraldez
- Department of Basic Medical Sciences, Medical School, Universidad de La Laguna, Tenerife, Spain; Instituto de Tecnologias Biomedicas, Universidad de La Laguna, Tenerife, Spain.
| |
Collapse
|
2
|
Li Q, Chen G, Yan J. Transmembrane determinants of voltage-gating differences between BK (Slo1) and Slo3 channels. Biophys J 2024; 123:2154-2166. [PMID: 38637987 PMCID: PMC11309983 DOI: 10.1016/j.bpj.2024.04.016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2023] [Revised: 02/01/2024] [Accepted: 04/15/2024] [Indexed: 04/20/2024] Open
Abstract
Voltage-gated potassium channels are critical in modulating cellular excitability, with Slo (slowpoke) channels forming a unique family characterized by their large conductance and dual regulation by electrical signals and intracellular messengers. Despite their structural and evolutionary similarities, Slo1 and Slo3 channels exhibit significant differences in their voltage-gating properties. This study investigates the molecular determinants that differentiate the voltage-gating properties of human Slo1 and mouse Slo3 channels. Utilizing Slo1/Slo3 chimeras, we pinpointed the selectivity filter region as a key factor in the Slo3 channel's reduced conductance at negative voltages. The S6 transmembrane (TM) segment was identified as pivotal for the Slo3 channel's biphasic deactivation kinetics at these voltages. Additionally, the S4 and S6 TM segments were found to be responsible for the gradual slope in the Slo3 channel's conductance-voltage relationship, while multiple TM regions appear to be involved in the Slo3 channel's requirement of strong depolarization for activation. Mutations in the Slo1's S5 and S6 TM segments revealed three residues (I233, L302, and M304) that likely play a crucial role in the allosteric coupling between the voltage sensors and the pore gate.
Collapse
Affiliation(s)
- Qin Li
- Department of Anesthesiology and Perioperative Medicine, The University of Texas MD Anderson Cancer Center, Houston, Texas; Molecular & Translational Biology and Neuroscience Programs, MD Anderson UT Health Graduate School of Biomedical Sciences, Houston, Texas
| | - Guanxing Chen
- Department of Anesthesiology and Perioperative Medicine, The University of Texas MD Anderson Cancer Center, Houston, Texas; Molecular & Translational Biology and Neuroscience Programs, MD Anderson UT Health Graduate School of Biomedical Sciences, Houston, Texas
| | - Jiusheng Yan
- Department of Anesthesiology and Perioperative Medicine, The University of Texas MD Anderson Cancer Center, Houston, Texas; Molecular & Translational Biology and Neuroscience Programs, MD Anderson UT Health Graduate School of Biomedical Sciences, Houston, Texas.
| |
Collapse
|
3
|
Lu A, Kimble M, Justinen S, Morris DP, Wang C, Martinez DE, Hessinger DA. BK Channels Function in Nematocyst Discharge from Vibration-Sensitive Cnidocyte Supporting Cell Complexes of the Sea Anemone Diadumene lineata. THE BIOLOGICAL BULLETIN 2023; 245:88-102. [PMID: 38976849 DOI: 10.1086/730702] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/10/2024]
Abstract
AbstractIntegrated chemo- and mechanosensory pathways, along with activated calcium influxes, regulate nematocyst discharge from sea anemone tentacles. Discharge from vibration-sensitive Type A cnidocyte supporting cell complexes use calcium-conducting transient receptor potential V4-like channels. Because calcium influxes often couple with calcium-activated, large-conductance potassium (BK) channels, we hypothesized that BK channels function in nematocyst discharge. To verify this hypothesis, we first tested five selective BK channel blockers on nematocyst-mediated prey killing in Diadumene lineata (aka Haliplanella luciae). All tested BK channel blockers inhibited prey killing at concentrations comparable to their inhibition of vertebrate BK channels. In addition, the BK channel blocker paxilline selectively inhibited prey killing mediated by vibration-sensitive Type A cnidocyte supporting cell complexes. We queried a mammalian BKα amino acid sequence to the Exaiptasia diaphena database, from which we identified a putative anemone, pore-forming BKα subunit sequence. Using the E. diaphena BKα sequence as a template, we assembled a BKα transcript from our assembled D. lineata transcriptome. In addition, the hydra homolog of D. lineata BKα localizes to nematocytes on the hydra single-cell RNA sequencing map. Our findings suggest that D. lineata expresses BK channels that play a role in vibration-sensitive nematocyst discharge from Type A cnidocyte supporting cell complexes. We believe this is the first functional demonstration of BK channels in nonbilaterians. Because stimulated chemoreceptors frequency tune Type A cnidocyte supporting cell complexes to frequencies matching swimming movements of prey via a protein kinase A signaling pathway and protein kinase A generally activates BK channels, we suggest that D. lineata BK channels may participate in protein kinase A-mediated frequency tuning.
Collapse
|
4
|
Cooray A, Kim J, Nirujan BR, Jayathilake NJ, Lee KP. Pharmacological Evidence Suggests That Slo3 Channel Is the Principal K + Channel in Boar Spermatozoa. Int J Mol Sci 2023; 24:ijms24097806. [PMID: 37175513 PMCID: PMC10178124 DOI: 10.3390/ijms24097806] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2023] [Revised: 04/20/2023] [Accepted: 04/23/2023] [Indexed: 05/15/2023] Open
Abstract
Sperm ion channels are associated with the quality and type of flagellar movement, and their differential regulation is crucial for sperm function during specific phases. The principal potassium ion channel is responsible for the majority of K+ ion flux, resulting in membrane hyperpolarization, and is essential for sperm capacitation-related signaling pathways. The molecular identity of the principal K+ channel varies greatly between different species, and there is a lack of information about boar K+ channels. We aimed to determine the channel identity of boar sperm contributing to the primary K+ current using pharmacological dissection. A series of Slo1 and Slo3 channel modulators were used for treatment. Sperm motility and related kinematic parameters were monitored using a computer-assisted sperm analysis system under non-capacitated conditions. Time-lapse flow cytometry with fluorochromes was used to measure changes in different intracellular ionic concentrations, and conventional flow cytometry was used to determine the acrosome reaction. Membrane depolarization, reduction in acrosome reaction, and motility parameters were observed upon the inhibition of the Slo3 channel, suggesting that the Slo3 gene encodes the main K+ channel in boar spermatozoa. The Slo3 channel was localized on the sperm flagellum, and the inhibition of Slo3 did not reduce sperm viability. These results may aid potential animal-model-based extrapolations and help to ameliorate motility and related parameters, leading to improved assisted reproductive methods in industrial livestock production.
Collapse
Affiliation(s)
- Akila Cooray
- Department of Physiology, College of Veterinary Medicine, Chungnam National University, Daejeon 34134, Republic of Korea
| | - Jeongsook Kim
- Department of Physiology, College of Veterinary Medicine, Chungnam National University, Daejeon 34134, Republic of Korea
| | - Beno Ramesh Nirujan
- Department of Physiology, College of Veterinary Medicine, Chungnam National University, Daejeon 34134, Republic of Korea
| | - Nishani Jayanika Jayathilake
- Department of Physiology, College of Veterinary Medicine, Chungnam National University, Daejeon 34134, Republic of Korea
| | - Kyu Pil Lee
- Department of Physiology, College of Veterinary Medicine, Chungnam National University, Daejeon 34134, Republic of Korea
| |
Collapse
|
5
|
Small molecule modulation of the Drosophila Slo channel elucidated by cryo-EM. Nat Commun 2021; 12:7164. [PMID: 34887422 PMCID: PMC8660915 DOI: 10.1038/s41467-021-27435-w] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2021] [Accepted: 11/18/2021] [Indexed: 12/16/2022] Open
Abstract
Slowpoke (Slo) potassium channels display extraordinarily high conductance, are synergistically activated by a positive transmembrane potential and high intracellular Ca2+ concentrations and are important targets for insecticides and antiparasitic drugs. However, it is unknown how these compounds modulate ion translocation and whether there are insect-specific binding pockets. Here, we report structures of Drosophila Slo in the Ca2+-bound and Ca2+-free form and in complex with the fungal neurotoxin verruculogen and the anthelmintic drug emodepside. Whereas the architecture and gating mechanism of Slo channels are conserved, potential insect-specific binding pockets exist. Verruculogen inhibits K+ transport by blocking the Ca2+-induced activation signal and precludes K+ from entering the selectivity filter. Emodepside decreases the conductance by suboptimal K+ coordination and uncouples ion gating from Ca2+ and voltage sensing. Our results expand the mechanistic understanding of Slo regulation and lay the foundation for the rational design of regulators of Slo and other voltage-gated ion channels. Slowpoke (Slo) channels are voltage-gated potassium channels that are activated by high intracellular Ca2+ concentrations, and they are targets for insecticides and antiparasitic drugs. Here, the authors present the cryo-EM structures of the Drosophila melanogaster Slo channel in the Ca2+-bound and Ca2+-free conformations, as well as in complex with the fungal neurotoxin verruculogen and the anthelmintic drug emodepside and discuss the mechanisms by which they affect the activity of Slo.
Collapse
|
6
|
Fan F, Chen Y, Chen Z, Guan L, Ye Z, Tang Y, Chen A, Lin C. Blockade of BK channels attenuates chronic visceral hypersensitivity in an IBS-like rat model. Mol Pain 2021; 17:17448069211040364. [PMID: 34407673 PMCID: PMC8381452 DOI: 10.1177/17448069211040364] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2021] [Revised: 07/08/2021] [Accepted: 07/31/2021] [Indexed: 12/17/2022] Open
Abstract
BACKGROUND Visceral hypersensitivity in irritable bowel syndrome (IBS) is still poorly understood, despite that chronic abdominal pain is the most common symptoms in IBS patients. To study effects of BK channels on visceral hypersensitivity in IBS rats and the underlying mechanisms, IBS rats were established by colorectal distention (CRD) in postnatal rats. The expression of large-conductance calcium and voltage-dependent potassium ion channels (BK channels) of the thoracolumbar spinal cord was examined in IBS and control rats. The effects of BK channel blockade on visceral hypersensitivity were evaluated. The interaction of BK channels and N-methyl-D-aspartate acid (NMDA) receptors was explored, and synaptic transmission at superficial dorsal horn (SDH) neurons of the thoracolumbar spinal cord was recorded by whole-cell patch clamp in IBS rats. RESULTS The expression of the BK channels of the thoracolumbar spinal cord in IBS rats was significantly reduced. The blockade of BK channels could reduce the visceral hypersensitivity in IBS rats. There was an interaction between BK channels and NMDA receptors in the spinal cord. The frequency of spontaneous inhibitory postsynaptic currents (sIPSCs) in SDH neurons is significantly reduced in IBS rats. The blockade of BK channels depolarizes the inhibitory interneuron membrane and increases their excitability in IBS rats. CONCLUSIONS BK channels could interact with NMDA receptors in the thoracolumbar spinal cord of rats and regulate visceral hypersensitivity in IBS rats.
Collapse
Affiliation(s)
- F Fan
- Nursing Department, Fujian Health College, China
- School of basic Medical Sciences, Laboratory of Pain Research,
Fujian Provincial Key Laboratory of Brain Aging and Neurodegenerative Diseases,
Fujian Medical University, China
| | - Y Chen
- School of basic Medical Sciences, Laboratory of Pain Research,
Fujian Provincial Key Laboratory of Brain Aging and Neurodegenerative Diseases,
Fujian Medical University, China
| | - Z Chen
- School of basic Medical Sciences, Laboratory of Pain Research,
Fujian Provincial Key Laboratory of Brain Aging and Neurodegenerative Diseases,
Fujian Medical University, China
| | - L Guan
- School of basic Medical Sciences, Laboratory of Pain Research,
Fujian Provincial Key Laboratory of Brain Aging and Neurodegenerative Diseases,
Fujian Medical University, China
| | - Z Ye
- School of basic Medical Sciences, Laboratory of Pain Research,
Fujian Provincial Key Laboratory of Brain Aging and Neurodegenerative Diseases,
Fujian Medical University, China
| | - Y Tang
- School of basic Medical Sciences, Laboratory of Pain Research,
Fujian Provincial Key Laboratory of Brain Aging and Neurodegenerative Diseases,
Fujian Medical University, China
| | - A Chen
- School of basic Medical Sciences, Laboratory of Pain Research,
Fujian Provincial Key Laboratory of Brain Aging and Neurodegenerative Diseases,
Fujian Medical University, China
| | - C Lin
- School of basic Medical Sciences, Laboratory of Pain Research,
Fujian Provincial Key Laboratory of Brain Aging and Neurodegenerative Diseases,
Fujian Medical University, China
| |
Collapse
|
7
|
Noda S, Suzuki Y, Yamamura H, Giles WR, Imaizumi Y. Roles of LRRC26 as an auxiliary γ1-subunit of large-conductance Ca 2+-activated K + channels in bronchial smooth muscle cells. Am J Physiol Lung Cell Mol Physiol 2020; 318:L366-L375. [PMID: 31800260 DOI: 10.1152/ajplung.00331.2019] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
In visceral smooth muscle cells (SMCs), the large-conductance Ca2+-activated K+ (BK) channel is one of the key elements underlying a negative feedback mechanism that is essential for the regulation of intracellular Ca2+ concentration. Although leucine-rich repeat-containing (LRRC) proteins have been identified as novel auxiliary γ-subunits of the BK channel (BKγ) in several cell types, its physiological roles in SMCs are unclear. The BKγ expression patterns in selected SM tissues were examined using real-time PCR analyses and Western blotting. The functional contribution of BKγ1 to BK channel activity was examined by whole cell patch-clamp in SMCs and heterologous expression systems. BKγ1 expression in mouse bronchial SMCs (mBSMCs) was higher than in other several SMC types. Coimmunoprecipitation and total internal reflection fluorescence imaging analyses revealed molecular interaction between BKα and BKγ1 in mBSMCs. Under voltage-clamp, steady-state activation of BK channel currents at pCa 8.0 in mBSMCs occurred in a voltage range comparable to that of reconstituted BKα/BKγ1 complex. However, this range was much more negative than in mouse aortic SMCs (mASMCs) or in HEK293 cells expressing BKα alone and β-subunit (BKβ1). Mallotoxin, a selective activator of BK channel that lacks BKγ1, dose-dependently activated BK currents in mASMCs but not in mBSMCs. The abundant expression of BKγ1 in mBSMCs extensively facilitates BK channel activity to keep the resting membrane potential at negative values and prevents contraction under physiological conditions.
Collapse
Affiliation(s)
- Sayuri Noda
- Department of Molecular and Cellular Pharmacology, Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya, Japan
| | - Yoshiaki Suzuki
- Department of Molecular and Cellular Pharmacology, Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya, Japan
| | - Hisao Yamamura
- Department of Molecular and Cellular Pharmacology, Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya, Japan
| | - Wayne R Giles
- Department of Physiology and Pharmacology, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Yuji Imaizumi
- Department of Molecular and Cellular Pharmacology, Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya, Japan
| |
Collapse
|
8
|
The functionally relevant site for paxilline inhibition of BK channels. Proc Natl Acad Sci U S A 2019; 117:1021-1026. [PMID: 31879339 DOI: 10.1073/pnas.1912623117] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The tremorgenic fungal alkaloid paxilline (PAX) is a commonly used specific inhibitor of the large-conductance, voltage- and Ca2+-dependent BK-type K+ channel. PAX inhibits BK channels by selective interaction with closed states. BK inhibition by PAX is best characterized by the idea that PAX gains access to the channel through the central cavity of the BK channel, and that only a single PAX molecule can interact with the BK channel at a time. The notion that PAX reaches its binding site via the central cavity and involves only a single PAX molecule would be consistent with binding on the axis of the permeation pathway, similar to classical open channel block and inconsistent with the observation that PAX selectively inhibits closed channels. To explore the potential sites of interaction of PAX with the BK channel, we undertook a computational analysis of the interaction of PAX with the BK channel pore gate domain guided by recently available liganded (open) and metal-free (closed) Aplysia BK channel structures. The analysis unambiguously identified a preferred position of PAX occupancy that accounts for all previously described features of PAX inhibition, including state dependence, G311 sensitivity, stoichiometry, and central cavity accessibility. This PAX-binding pose in closed BK channels is supported by additional functional results.
Collapse
|
9
|
Yeste M, Llavanera M, Pérez G, Scornik F, Puig-Parri J, Brugada R, Bonet S, Pinart E. Elucidating the Role of K + Channels during In Vitro Capacitation of Boar Spermatozoa: Do SLO1 Channels Play a Crucial Role? Int J Mol Sci 2019; 20:E6330. [PMID: 31847486 PMCID: PMC6940911 DOI: 10.3390/ijms20246330] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2019] [Revised: 12/05/2019] [Accepted: 12/13/2019] [Indexed: 01/16/2023] Open
Abstract
This study sought to identify and localize SLO1 channels in boar spermatozoa by immunoblotting and immunofluorescence, and to determine their physiological role during in vitro sperm capacitation. Sperm samples from 14 boars were incubated in a capacitation medium for 300 min in the presence of paxilline (PAX), a specific SLO1-channel blocker, added either at 0 min or after 240 min of incubation. Negative controls were incubated in capacitation medium, and positive controls in capacitation medium plus tetraethyl ammonium (TEA), a general K+-channel blocker, also added at 0 min or after 240 min of incubation. In all samples, acrosome exocytosis was triggered with progesterone after 240 min of incubation. Sperm motility and kinematics, integrity of plasma and acrosome membranes, membrane lipid disorder, intracellular calcium levels and acrosin activity were evaluated after 0, 60, 120, 180, 240, 250, 270 and 300 min of incubation. In boar spermatozoa, SLO1 channels were found to have 80 kDa and be localized in the anterior postacrosomal region and the mid and principal piece of the tail; their specific blockage through PAX resulted in altered calcium levels and acrosome exocytosis. As expected, TEA blocker impaired in vitro sperm capacitation, by altering sperm motility and kinematics and calcium levels. In conclusion, SLO1 channels are crucial for the acrosome exocytosis induced by progesterone in in vitro capacitated boar spermatozoa.
Collapse
Affiliation(s)
- Marc Yeste
- Unit of Cell Biology, Biotechnology of Animal and Human Reproduction (TechnoSperm), Department of Biology, Faculty of Sciences, Institute of Food and Agricultural Technology, University of Girona, E-17003 Girona, Spain; (M.Y.); (M.L.); (J.P.-P.); (S.B.)
| | - Marc Llavanera
- Unit of Cell Biology, Biotechnology of Animal and Human Reproduction (TechnoSperm), Department of Biology, Faculty of Sciences, Institute of Food and Agricultural Technology, University of Girona, E-17003 Girona, Spain; (M.Y.); (M.L.); (J.P.-P.); (S.B.)
| | - Guillermo Pérez
- Department of Medical Sciences, Faculty of Medicine, University of Girona, E-17003 Girona, Spain; (G.P.); (F.S.); (R.B.)
- Cardiovascular Genetics Group, Girona Biomedical Research Institute (IDIBGI), E-17190 Girona, Spain
- Biomedical Research Networking Center on Cardiovascular Diseases (CIBERCV), E-28029 Madrid, Spain
| | - Fabiana Scornik
- Department of Medical Sciences, Faculty of Medicine, University of Girona, E-17003 Girona, Spain; (G.P.); (F.S.); (R.B.)
- Cardiovascular Genetics Group, Girona Biomedical Research Institute (IDIBGI), E-17190 Girona, Spain
- Biomedical Research Networking Center on Cardiovascular Diseases (CIBERCV), E-28029 Madrid, Spain
| | - Josep Puig-Parri
- Unit of Cell Biology, Biotechnology of Animal and Human Reproduction (TechnoSperm), Department of Biology, Faculty of Sciences, Institute of Food and Agricultural Technology, University of Girona, E-17003 Girona, Spain; (M.Y.); (M.L.); (J.P.-P.); (S.B.)
| | - Ramon Brugada
- Department of Medical Sciences, Faculty of Medicine, University of Girona, E-17003 Girona, Spain; (G.P.); (F.S.); (R.B.)
- Cardiovascular Genetics Group, Girona Biomedical Research Institute (IDIBGI), E-17190 Girona, Spain
- Biomedical Research Networking Center on Cardiovascular Diseases (CIBERCV), E-28029 Madrid, Spain
- Cardiology Service, Hospital Josep Trueta, E-17003 Girona, Spain
| | - Sergi Bonet
- Unit of Cell Biology, Biotechnology of Animal and Human Reproduction (TechnoSperm), Department of Biology, Faculty of Sciences, Institute of Food and Agricultural Technology, University of Girona, E-17003 Girona, Spain; (M.Y.); (M.L.); (J.P.-P.); (S.B.)
| | - Elisabeth Pinart
- Unit of Cell Biology, Biotechnology of Animal and Human Reproduction (TechnoSperm), Department of Biology, Faculty of Sciences, Institute of Food and Agricultural Technology, University of Girona, E-17003 Girona, Spain; (M.Y.); (M.L.); (J.P.-P.); (S.B.)
| |
Collapse
|
10
|
Zhou Y, Xia XM, Lingle CJ. BK channel inhibition by strong extracellular acidification. eLife 2018; 7:38060. [PMID: 29963986 PMCID: PMC6054526 DOI: 10.7554/elife.38060] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2018] [Accepted: 07/01/2018] [Indexed: 12/24/2022] Open
Abstract
Mammalian BK-type voltage- and Ca2+-dependent K+ channels are found in a wide range of cells and intracellular organelles. Among different loci, the composition of the extracellular microenvironment, including pH, may differ substantially. For example, it has been reported that BK channels are expressed in lysosomes with their extracellular side facing the strongly acidified lysosomal lumen (pH ~4.5). Here we show that BK activation is strongly and reversibly inhibited by extracellular H+, with its conductance-voltage relationship shifted by more than +100 mV at pHO 4. Our results reveal that this inhibition is mainly caused by H+ inhibition of BK voltage-sensor (VSD) activation through three acidic residues on the extracellular side of BK VSD. Given that these key residues (D133, D147, D153) are highly conserved among members in the voltage-dependent cation channel superfamily, the mechanism underlying BK inhibition by extracellular acidification might also be applicable to other members in the family.
Collapse
Affiliation(s)
- Yu Zhou
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, United States
| | - Xiao-Ming Xia
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, United States
| | - Christopher J Lingle
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, United States
| |
Collapse
|
11
|
Latorre R, Castillo K, Carrasquel-Ursulaez W, Sepulveda RV, Gonzalez-Nilo F, Gonzalez C, Alvarez O. Molecular Determinants of BK Channel Functional Diversity and Functioning. Physiol Rev 2017; 97:39-87. [DOI: 10.1152/physrev.00001.2016] [Citation(s) in RCA: 151] [Impact Index Per Article: 21.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Large-conductance Ca2+- and voltage-activated K+ (BK) channels play many physiological roles ranging from the maintenance of smooth muscle tone to hearing and neurosecretion. BK channels are tetramers in which the pore-forming α subunit is coded by a single gene ( Slowpoke, KCNMA1). In this review, we first highlight the physiological importance of this ubiquitous channel, emphasizing the role that BK channels play in different channelopathies. We next discuss the modular nature of BK channel-forming protein, in which the different modules (the voltage sensor and the Ca2+ binding sites) communicate with the pore gates allosterically. In this regard, we review in detail the allosteric models proposed to explain channel activation and how the models are related to channel structure. Considering their extremely large conductance and unique selectivity to K+, we also offer an account of how these two apparently paradoxical characteristics can be understood consistently in unison, and what we have learned about the conduction system and the activation gates using ions, blockers, and toxins. Attention is paid here to the molecular nature of the voltage sensor and the Ca2+ binding sites that are located in a gating ring of known crystal structure and constituted by four COOH termini. Despite the fact that BK channels are coded by a single gene, diversity is obtained by means of alternative splicing and modulatory β and γ subunits. We finish this review by describing how the association of the α subunit with β or with γ subunits can change the BK channel phenotype and pharmacology.
Collapse
Affiliation(s)
- Ramon Latorre
- Centro Interdisciplinario de Neurociencia de Valparaíso and Doctorado en Ciencias Mención Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile; Universidad Andres Bello, Facultad de Ciencias Biologicas, Center for Bioinformatics and Integrative Biology, Avenida Republica 239, Santiago, Chile and Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago, Chile
| | - Karen Castillo
- Centro Interdisciplinario de Neurociencia de Valparaíso and Doctorado en Ciencias Mención Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile; Universidad Andres Bello, Facultad de Ciencias Biologicas, Center for Bioinformatics and Integrative Biology, Avenida Republica 239, Santiago, Chile and Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago, Chile
| | - Willy Carrasquel-Ursulaez
- Centro Interdisciplinario de Neurociencia de Valparaíso and Doctorado en Ciencias Mención Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile; Universidad Andres Bello, Facultad de Ciencias Biologicas, Center for Bioinformatics and Integrative Biology, Avenida Republica 239, Santiago, Chile and Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago, Chile
| | - Romina V. Sepulveda
- Centro Interdisciplinario de Neurociencia de Valparaíso and Doctorado en Ciencias Mención Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile; Universidad Andres Bello, Facultad de Ciencias Biologicas, Center for Bioinformatics and Integrative Biology, Avenida Republica 239, Santiago, Chile and Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago, Chile
| | - Fernando Gonzalez-Nilo
- Centro Interdisciplinario de Neurociencia de Valparaíso and Doctorado en Ciencias Mención Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile; Universidad Andres Bello, Facultad de Ciencias Biologicas, Center for Bioinformatics and Integrative Biology, Avenida Republica 239, Santiago, Chile and Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago, Chile
| | - Carlos Gonzalez
- Centro Interdisciplinario de Neurociencia de Valparaíso and Doctorado en Ciencias Mención Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile; Universidad Andres Bello, Facultad de Ciencias Biologicas, Center for Bioinformatics and Integrative Biology, Avenida Republica 239, Santiago, Chile and Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago, Chile
| | - Osvaldo Alvarez
- Centro Interdisciplinario de Neurociencia de Valparaíso and Doctorado en Ciencias Mención Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile; Universidad Andres Bello, Facultad de Ciencias Biologicas, Center for Bioinformatics and Integrative Biology, Avenida Republica 239, Santiago, Chile and Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago, Chile
| |
Collapse
|
12
|
Bisen S, Seleverstov O, Belani J, Rychnovsky S, Dopico AM, Bukiya AN. Distinct mechanisms underlying cholesterol protection against alcohol-induced BK channel inhibition and resulting vasoconstriction. BIOCHIMICA ET BIOPHYSICA ACTA 2016; 1861:1756-1766. [PMID: 27565113 PMCID: PMC5274633 DOI: 10.1016/j.bbalip.2016.08.013] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/04/2016] [Revised: 07/21/2016] [Accepted: 08/22/2016] [Indexed: 02/01/2023]
Abstract
Alcohol (ethanol) at concentrations reached in blood following moderate to heavy drinking (30-80mM) reduces cerebral artery diameter via inhibition of voltage- and calcium-gated potassium channels of large conductance (BK) in cerebral artery smooth muscle. These channels consist of channel-forming α and regulatory β1 subunits. A high-cholesterol diet protects against ethanol-induced constriction via accumulation of cholesterol within the vasculature. The molecular mechanisms of this protection remain unknown. In the present work, we demonstrate that in vitro cholesterol enrichment of rat middle cerebral arteries significantly increased cholesterol within arterial tissues and blunted constriction by 50mM of ethanol. Ethanol-induced BK channel inhibition in inside-out patches excised from freshly isolated cerebral artery myocytes was also abolished by cholesterol enrichment. Enrichment of arteries with enantiomeric cholesterol (ent-cholesterol) also blunted BK channel inhibition and cerebral artery constriction in response to ethanol. The similar protection of cholesterol and ent-cholesterol against ethanol action indicates that this protection does not require protein site(s) that specifically sense natural cholesterol. Cholesterol-driven protection against ethanol-induced BK channel inhibition and vasoconstriction was replicated in myocytes and middle cerebral arteries of C57BL/6 mice. BK β1 subunits are known to regulate vascular diameter and its modification by ethanol. However, blunting of an ethanol effect by in vitro cholesterol enrichment was observed in arteries and myocyte membrane patches from BK β1 (KCNMB1) knockout mice. Thus, BK β1 subunits are not needed for cholesterol protection against ethanol effect on BK channel function and cerebral artery diameter.
Collapse
Affiliation(s)
- Shivantika Bisen
- Department of Pharmacology, The University of Tennessee Health Science Center, Memphis, TN 38163, USA
| | - Olga Seleverstov
- Department of Pharmacology, The University of Tennessee Health Science Center, Memphis, TN 38163, USA
| | - Jitendra Belani
- Department of Chemistry, School of Physical Sciences, University of California, Irvine, 3038B FRH, Mail Code: 2025, Irvine, CA 92697, USA
| | - Scott Rychnovsky
- Department of Chemistry, School of Physical Sciences, University of California, Irvine, 3038B FRH, Mail Code: 2025, Irvine, CA 92697, USA
| | - Alex M Dopico
- Department of Pharmacology, The University of Tennessee Health Science Center, Memphis, TN 38163, USA
| | - Anna N Bukiya
- Department of Pharmacology, The University of Tennessee Health Science Center, Memphis, TN 38163, USA.
| |
Collapse
|
13
|
Abstract
BK channels are universal regulators of cell excitability, given their exceptional unitary conductance selective for K(+), joint activation mechanism by membrane depolarization and intracellular [Ca(2+)] elevation, and broad expression pattern. In this chapter, we discuss the structural basis and operational principles of their activation, or gating, by membrane potential and calcium. We also discuss how the two activation mechanisms interact to culminate in channel opening. As members of the voltage-gated potassium channel superfamily, BK channels are discussed in the context of archetypal family members, in terms of similarities that help us understand their function, but also seminal structural and biophysical differences that confer unique functional properties.
Collapse
Affiliation(s)
- A Pantazis
- David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, CA, United States
| | - R Olcese
- David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, CA, United States.
| |
Collapse
|
14
|
Zhou Y, Lingle CJ. Paxilline inhibits BK channels by an almost exclusively closed-channel block mechanism. ACTA ACUST UNITED AC 2015; 144:415-40. [PMID: 25348413 PMCID: PMC4210426 DOI: 10.1085/jgp.201411259] [Citation(s) in RCA: 101] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Paxilline, a tremorogenic fungal alkaloid, potently inhibits large conductance Ca(2+)- and voltage-activated K(+) (BK)-type channels, but little is known about the mechanism underlying this inhibition. Here we show that inhibition is inversely dependent on BK channel open probability (Po), and is fully relieved by conditions that increase Po, even in the constant presence of paxilline. Manipulations that shift BK gating to more negative potentials reduce inhibition by paxilline in accordance with the increase in channel Po. Measurements of Po times the number of channels at negative potentials support the idea that paxilline increases occupancy of closed states, effectively reducing the closed-open equilibrium constant, L(0). Gating current measurements exclude an effect of paxilline on voltage sensors. Steady-state inhibition by multiple paxilline concentrations was determined for four distinct equilibration conditions, each with a distinct Po. The IC50 for paxilline shifted from around 10 nM when channels were largely closed to near 10 µM as maximal Po was approached. Model-dependent analysis suggests a mechanism of inhibition in which binding of a single paxilline molecule allosterically alters the intrinsic L(0) favoring occupancy of closed states, with affinity for the closed conformation being >500-fold greater than affinity for the open conformation. The rate of inhibition of closed channels was linear up through 2 µM paxilline, with a slope of 2 × 10(6) M(-1)s(-1). Paxilline inhibition was hindered by either the bulky cytosolic blocker, bbTBA, or by concentrations of cytosolic sucrose that hinder ion permeation. However, paxilline does not hinder MTSET modification of the inner cavity residue, A313C. We conclude that paxilline binds more tightly to the closed conformation, favoring occupancy of closed-channel conformations, and propose that it binds to a superficial position near the entrance to the central cavity, but does not hinder access of smaller molecules to this cavity.
Collapse
Affiliation(s)
- Yu Zhou
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO 63110
| | - Christopher J Lingle
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO 63110
| |
Collapse
|
15
|
McManus OB, Rothberg BS. An old probe sheds new light on BK channel pore structure. ACTA ACUST UNITED AC 2014; 144:499-501. [PMID: 25385785 PMCID: PMC4242814 DOI: 10.1085/jgp.201411306] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Affiliation(s)
| | - Brad S Rothberg
- Department of Medical Genetics and Molecular Biochemistry, Temple University School of Medicine, Philadelphia, PA 19140
| |
Collapse
|
16
|
Joerk A, Seidel RA, Walter SG, Wiegand A, Kahnes M, Klopfleisch M, Kirmse K, Pohnert G, Westerhausen M, Witte OW, Holthoff K. Impact of heme and heme degradation products on vascular diameter in mouse visual cortex. J Am Heart Assoc 2014; 3:jah3660. [PMID: 25169792 PMCID: PMC4310418 DOI: 10.1161/jaha.114.001220] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
BACKGROUND Delayed cerebral vasospasm is the most common cause of mortality and severe neurological impairment in patients who survive subarachnoid hemorrhage. Despite improvements in the field of diagnostic imaging, options for prevention and medical treatment-primarily with the calcium channel antagonist nimodipine or hemodynamic manipulations-are insufficient. Previous studies have suggested that heme and bilirubin oxidation end products, originating from degraded hemoglobin around ruptured blood vessels, are involved in the development of vasospasm by inhibiting large conductance BKC a potassium channels in vascular smooth muscle cells. In this study, we identify individual heme degradation products regulating arteriolar diameter in dependence of BKC a channel activity. METHODS AND RESULTS Using differential interference contrast video microscopy in acute brain slices, we determined diameter changes of intracerebral arterioles in mouse visual cortex. In preconstricted vessels, the specific BKC a channel blockers paxilline and iberiotoxin as well as iron-containing hemin caused vasoconstriction. In addition, the bilirubin oxidation end product Z-BOX A showed a stronger vasoconstrictive potency than its regio-isomer Z-BOX B. Importantly, Z-BOX A had the same vasoconstrictive effect, independent of its origin from oxidative degradation or chemical synthesis. Finally, in slices of Slo1-deficient knockout mice, paxilline and Z-BOX A remained ineffective in changing arteriole diameter. CONCLUSIONS We identified individual components of the oxidative bilirubin degradation that led to vasoconstriction of cerebral arterioles. The vasoconstrictive effect of Z-BOX A and Z-BOX B was mediated by BKC a channel activity that might represent a signaling pathway in the occurrence of delayed cerebral vasospasm in subarachnoid hemorrhage patients.
Collapse
Affiliation(s)
- Alexander Joerk
- Hans‐Berger Department of Neurology, University Hospital Jena, Germany (A.J., S.G.W., A.W., K.K., O.W.W., K.H.)
| | - Raphael Andreas Seidel
- Institute of Inorganic and Analytical Chemistry, Friedrich‐Schiller University, Jena, Germany (R.A.S., M.K., M.K., G.P., M.W.)
- Department of Anesthesiology and Intensive Care Medicine/Center for Sepsis Control and Care, University Hospital, Friedrich Schiller University, Jena, Germany (R.A.S.)
| | - Sebastian Gottfried Walter
- Hans‐Berger Department of Neurology, University Hospital Jena, Germany (A.J., S.G.W., A.W., K.K., O.W.W., K.H.)
| | - Anne Wiegand
- Hans‐Berger Department of Neurology, University Hospital Jena, Germany (A.J., S.G.W., A.W., K.K., O.W.W., K.H.)
| | - Marcel Kahnes
- Institute of Inorganic and Analytical Chemistry, Friedrich‐Schiller University, Jena, Germany (R.A.S., M.K., M.K., G.P., M.W.)
| | - Maurice Klopfleisch
- Institute of Inorganic and Analytical Chemistry, Friedrich‐Schiller University, Jena, Germany (R.A.S., M.K., M.K., G.P., M.W.)
| | - Knut Kirmse
- Hans‐Berger Department of Neurology, University Hospital Jena, Germany (A.J., S.G.W., A.W., K.K., O.W.W., K.H.)
| | - Georg Pohnert
- Institute of Inorganic and Analytical Chemistry, Friedrich‐Schiller University, Jena, Germany (R.A.S., M.K., M.K., G.P., M.W.)
| | - Matthias Westerhausen
- Institute of Inorganic and Analytical Chemistry, Friedrich‐Schiller University, Jena, Germany (R.A.S., M.K., M.K., G.P., M.W.)
| | - Otto Wilhelm Witte
- Hans‐Berger Department of Neurology, University Hospital Jena, Germany (A.J., S.G.W., A.W., K.K., O.W.W., K.H.)
| | - Knut Holthoff
- Hans‐Berger Department of Neurology, University Hospital Jena, Germany (A.J., S.G.W., A.W., K.K., O.W.W., K.H.)
| |
Collapse
|
17
|
Tang QY, Zhang Z, Meng XY, Cui M, Logothetis DE. Structural determinants of phosphatidylinositol 4,5-bisphosphate (PIP2) regulation of BK channel activity through the RCK1 Ca2+ coordination site. J Biol Chem 2014; 289:18860-72. [PMID: 24778177 DOI: 10.1074/jbc.m113.538033] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Big or high conductance potassium (BK) channels are activated by voltage and intracellular calcium (Ca(2+)). Phosphatidylinositol 4,5-bisphosphate (PIP2), a ubiquitous modulator of ion channel activity, has been reported to enhance Ca(2+)-driven gating of BK channels, but a molecular understanding of this interplay or even of the PIP2 regulation of this channel's activity remains elusive. Here, we identify structural determinants in the KDRDD loop (which follows the αA helix in the RCK1 domain) to be responsible for the coupling between Ca(2+) and PIP2 in regulating BK channel activity. In the absence of Ca(2+), RCK1 structural elements limit channel activation through a decrease in the channel's PIP2 apparent affinity. This inhibitory influence of BK channel activation can be relieved by mutation of residues that (a) connect either the RCK1 Ca(2+) coordination site (Asp(367) or its flanking basic residues in the KDRDD loop) to the PIP2-interacting residues (Lys(392) and Arg(393)) found in the αB helix or (b) are involved in hydrophobic interactions between the αA and αB helix of the RCK1 domain. In the presence of Ca(2+), the RCK1-inhibitory influence of channel-PIP2 interactions and channel activity is relieved by Ca(2+) engaging Asp(367). Our results demonstrate that, along with Ca(2+) and voltage, PIP2 is a third factor critical to the integral control of BK channel activity.
Collapse
Affiliation(s)
- Qiong-Yao Tang
- From the Department of Physiology and Biophysics, Virginia Commonwealth University School of Medicine, Richmond, Virginia 23298 and the Jiangsu Province Key Laboratory of Anesthesiology and Jiangsu Province Key Laboratory of Anesthesia and Analgesia Application Technology, Xuzhou Medical College, Xuzhou 221004, China
| | - Zhe Zhang
- From the Department of Physiology and Biophysics, Virginia Commonwealth University School of Medicine, Richmond, Virginia 23298 and the Jiangsu Province Key Laboratory of Anesthesiology and Jiangsu Province Key Laboratory of Anesthesia and Analgesia Application Technology, Xuzhou Medical College, Xuzhou 221004, China
| | - Xuan-Yu Meng
- From the Department of Physiology and Biophysics, Virginia Commonwealth University School of Medicine, Richmond, Virginia 23298 and
| | - Meng Cui
- From the Department of Physiology and Biophysics, Virginia Commonwealth University School of Medicine, Richmond, Virginia 23298 and
| | - Diomedes E Logothetis
- From the Department of Physiology and Biophysics, Virginia Commonwealth University School of Medicine, Richmond, Virginia 23298 and
| |
Collapse
|
18
|
Hoshi T, Xu R, Hou S, Heinemann SH, Tian Y. A point mutation in the human Slo1 channel that impairs its sensitivity to omega-3 docosahexaenoic acid. ACTA ACUST UNITED AC 2013; 142:507-22. [PMID: 24127525 PMCID: PMC3813383 DOI: 10.1085/jgp.201311061] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Long-chain polyunsaturated omega-3 fatty acids such as docosahexaenoic acid (DHA) at nanomolar concentrations reversibly activate human large-conductance Ca2+- and voltage-gated K+ (Slo1 BK) channels containing auxiliary β1 or β4 subunits in cell-free patches. Here we examined the action of DHA on the Slo1 channel without any auxiliary subunit and sought to elucidate the biophysical mechanism and the molecular determinants of the DHA sensitivity. Measurements of ionic currents through human Slo1 (hSlo1) channels reveal that the stimulatory effect of DHA does not require activation of the voltage or Ca2+ sensors. Unlike gating of the hSlo1 channel, that of the Drosophila melanogaster Slo1 (dSlo1) channel is unaltered by DHA. Our mutagenesis study based on the differential responses of human and dSlo1 channels to DHA pinpoints that Y318 near the cytoplasmic end of S6 in the hSlo1 channel is a critical determinant of the stimulatory action of DHA. The mutation Y318S in hSlo1, which replaces Y with S as found in dSlo1, greatly diminishes the channel’s response to DHA with a 22-carbon chain whether β1 or β4 is absent or present. However, the responses to α-linolenic acid, an omegea-3 fatty acid with an 18-carbon chain, and to arachidonic acid, an omega-6 fatty acid with a 20-carbon chain, remain unaffected by the mutation. Y318 in the S6 segment of hSlo1 is thus an important determinant of the electrophysiological response of the channel to DHA. Furthermore, the mutation Y318S may prove to be useful in dissecting out the complex lipid-mediated modulation of Slo1 BK channels.
Collapse
Affiliation(s)
- Toshinori Hoshi
- Department of Physiology, University of Pennsylvania, Philadelphia, PA 19104
| | | | | | | | | |
Collapse
|
19
|
Mannowetz N, Naidoo NM, Choo SAS, Smith JF, Lishko PV. Slo1 is the principal potassium channel of human spermatozoa. eLife 2013; 2:e01009. [PMID: 24137539 PMCID: PMC3789364 DOI: 10.7554/elife.01009] [Citation(s) in RCA: 78] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2013] [Accepted: 09/02/2013] [Indexed: 12/21/2022] Open
Abstract
Mammalian spermatozoa gain competence to fertilize an oocyte as they travel through the female reproductive tract. This process is accompanied by an elevation of sperm intracellular calcium and a membrane hyperpolarization. The latter is evoked by K(+) efflux; however, the molecular identity of the potassium channel of human spermatozoa (hKSper) is unknown. Here, we characterize hKSper, reporting that it is regulated by intracellular calcium but is insensitive to intracellular alkalinization. We also show that human KSper is inhibited by charybdotoxin, iberiotoxin, and paxilline, while mouse KSper is insensitive to these compounds. Such unique properties suggest that the Slo1 ion channel is the molecular determinant for hKSper. We show that Slo1 is localized to the sperm flagellum and is inhibited by progesterone. Inhibition of hKSper by progesterone may depolarize the spermatozoon to open the calcium channel CatSper, thus raising [Ca(2+)] to produce hyperactivation and allowing sperm to fertilize an oocyte. DOI:http://dx.doi.org/10.7554/eLife.01009.001.
Collapse
Affiliation(s)
- Nadja Mannowetz
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States
| | - Natasha M Naidoo
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States
| | - Seung-A Sara Choo
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States
| | - James F Smith
- Department of Urology, University of California, San Francisco, San Francisco, United States
| | - Polina V Lishko
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States
| |
Collapse
|
20
|
Malysz J, Rovner ES, Petkov GV. Single-channel biophysical and pharmacological characterizations of native human large-conductance calcium-activated potassium channels in freshly isolated detrusor smooth muscle cells. Pflugers Arch 2013; 465:965-75. [PMID: 23344746 PMCID: PMC3659209 DOI: 10.1007/s00424-012-1214-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2012] [Revised: 12/27/2012] [Accepted: 12/29/2012] [Indexed: 10/27/2022]
Abstract
Recent studies have demonstrated the importance of large-conductance Ca(2+)-activated K(+) (BK) channels in detrusor smooth muscle (DSM) function in vitro and in vivo. However, in-depth characterization of human native DSM single BK channels has not yet been provided. Here, we conducted single-channel recordings from excised patches from native human DSM cells. Inside-out and outside-out recordings in high K(+) symmetrical solution (containing 140 mM KCl and ~300 nM free Ca(2+)) showed single-channel conductance of 215-220 pS, half-maximum constant for activation of ~+75 to +80 mV, and low probability of opening (P o) at +20 mV that increased ~10-fold at +40 mV and ~60-fold at +60 mV. Using the inside-out configuration at +30 mV, reduction of intracellular [Ca(2+)] from ~300 nM to Ca(2+)-free decreased the P o by ~85 %, whereas elevation to ~800 nM increased P o by ~50-fold. The BK channel activator NS1619 (10 μM) enhanced the P o by ~10-fold at +30 mV; subsequent application of the selective BK channel inhibitor paxilline (500 nM) blocked the activity. Changes in intracellular [Ca(2+)] or the addition of NS1619 did not significantly alter the current amplitude or single-channel conductance. This is the first report to provide biophysical and pharmacological profiles of native human DSM single BK channels highlighting their importance in regulating human DSM excitability.
Collapse
Affiliation(s)
- John Malysz
- Department of Pharmaceutical and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Columbia, SC 29208
| | - Eric S. Rovner
- Medical University of South Carolina, Charleston, SC 29425
| | - Georgi V. Petkov
- Department of Pharmaceutical and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Columbia, SC 29208
- Medical University of South Carolina, Charleston, SC 29425
| |
Collapse
|
21
|
Zhang J, Halm ST, Halm DR. Role of the BK channel (KCa1.1) during activation of electrogenic K+ secretion in guinea pig distal colon. Am J Physiol Gastrointest Liver Physiol 2012; 303:G1322-34. [PMID: 23064759 PMCID: PMC3532550 DOI: 10.1152/ajpgi.00325.2012] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Secretagogues acting at a variety of receptor types activate electrogenic K(+) secretion in guinea pig distal colon, often accompanied by Cl(-) secretion. Distinct blockers of K(Ca)1.1 (BK, Kcnma1), iberiotoxin (IbTx), and paxilline inhibited the negative short-circuit current (I(sc)) associated with K(+) secretion. Mucosal addition of IbTx inhibited epinephrine-activated I(sc) ((epi)I(sc)) and transepithelial conductance ((epi)G(t)) consistent with K(+) secretion occurring via apical membrane K(Ca)1.1. The concentration dependence of IbTx inhibition of (epi)I(sc) yielded an IC(50) of 193 nM, with a maximal inhibition of 51%. Similarly, IbTx inhibited (epi)G(t) with an IC(50) of 220 nM and maximal inhibition of 48%. Mucosally added paxilline (10 μM) inhibited (epi)I(sc) and (epi)G(t) by ∼50%. IbTx and paxilline also inhibited I(sc) activated by mucosal ATP, supporting apical K(Ca)1.1 as a requirement for this K(+) secretagogue. Responses to IbTx and paxilline indicated that a component of K(+) secretion occurred during activation of Cl(-) secretion by prostaglandin-E(2) and cholinergic stimulation. Analysis of K(Ca)1.1α mRNA expression in distal colonic epithelial cells indicated the presence of the ZERO splice variant and three splice variants for the COOH terminus. The presence of the regulatory β-subunits K(Ca)β1 and K(Ca)β4 also was demonstrated. Immunolocalization supported the presence of K(Ca)1.1α in apical and basolateral membranes of surface and crypt cells. Together these results support a cellular mechanism for electrogenic K(+) secretion involving apical membrane K(Ca)1.1 during activation by several secretagogue types, but the observed K(+) secretion likely required the activity of additional K(+) channel types in the apical membrane.
Collapse
Affiliation(s)
- Jin Zhang
- Department of Neuroscience, Cell Biology and Physiology, Wright State University Boonshoft School of Medicine, Dayton, Ohio
| | - Susan T. Halm
- Department of Neuroscience, Cell Biology and Physiology, Wright State University Boonshoft School of Medicine, Dayton, Ohio
| | - Dan R. Halm
- Department of Neuroscience, Cell Biology and Physiology, Wright State University Boonshoft School of Medicine, Dayton, Ohio
| |
Collapse
|
22
|
Chen L, Zhang J, He Y, Pan J, Zhou H, Li H, Tang Y, Zheng Y. Contribution of BK(Ca) channels of neurons in rostral ventrolateral medulla to CO-mediated central regulation of respiratory rhythm in medullary slices of neonatal rats. Respir Physiol Neurobiol 2012; 182:93-9. [PMID: 22633934 DOI: 10.1016/j.resp.2012.05.006] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2012] [Revised: 04/12/2012] [Accepted: 05/06/2012] [Indexed: 10/28/2022]
Abstract
We recently described that carbon monoxide (CO) participated in the regulation of rhythmic respiration in medullary slices. The present study was undertaken to further assess whether the large-conductance calcium-activated potassium channels (BK(Ca) channels) are involved in the CO-mediated central regulation of respiratory rhythm in medullary slices. The rhythmic discharge of hypoglossal rootlets of medullary slices of neonatal rats was recorded. We observed that blocking BK(Ca) channels could partially abolish the effects of CO on the rhythmic bursts of hypoglossal rootlets. With whole-cell patch-clamp recording technique, we further observed that CO could reversibly augment potassium current density of the neurons in the rostral ventrolateral medulla. The CO-induced increase in potassium current was entirely blocked by the pretreatment of slices with BK(Ca) channels blocker; whereas blockade of CO generation with zinc protoporphyrin-IX produced an opposite response. Altogether, these data indicate that BK(Ca) channels of the neurons in neonatal rostral ventrolateral medulla could be activated by CO and involved in CO-mediated central regulation of respiratory rhythm in medullary slices.
Collapse
Affiliation(s)
- Li Chen
- Department of Physiology, West China School of Preclinical and Forensic Medicine, Sichuan University, Chengdu, PR China
| | | | | | | | | | | | | | | |
Collapse
|
23
|
Prole DL, Marrion NV. Identification of putative potassium channel homologues in pathogenic protozoa. PLoS One 2012; 7:e32264. [PMID: 22363819 PMCID: PMC3283738 DOI: 10.1371/journal.pone.0032264] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2011] [Accepted: 01/24/2012] [Indexed: 12/21/2022] Open
Abstract
K+ channels play a vital homeostatic role in cells and abnormal activity of these channels can dramatically alter cell function and survival, suggesting that they might be attractive drug targets in pathogenic organisms. Pathogenic protozoa lead to diseases such as malaria, leishmaniasis, trypanosomiasis and dysentery that are responsible for millions of deaths each year worldwide. The genomes of many protozoan parasites have recently been sequenced, allowing rational design of targeted therapies. We analyzed the genomes of pathogenic protozoa and show the existence within them of genes encoding putative homologues of K+ channels. These protozoan K+ channel homologues represent novel targets for anti-parasitic drugs. Differences in the sequences and diversity of human and parasite proteins may allow pathogen-specific targeting of these K+ channel homologues.
Collapse
Affiliation(s)
- David L Prole
- Department of Pharmacology, University of Cambridge, Cambridge, United Kingdom.
| | | |
Collapse
|
24
|
Wojtovich AP, Sherman TA, Nadtochiy SM, Urciuoli WR, Brookes PS, Nehrke K. SLO-2 is cytoprotective and contributes to mitochondrial potassium transport. PLoS One 2011; 6:e28287. [PMID: 22145034 PMCID: PMC3228735 DOI: 10.1371/journal.pone.0028287] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2011] [Accepted: 11/04/2011] [Indexed: 11/19/2022] Open
Abstract
Mitochondrial potassium channels are important mediators of cell protection against stress. The mitochondrial large-conductance "big" K(+) channel (mBK) mediates the evolutionarily-conserved process of anesthetic preconditioning (APC), wherein exposure to volatile anesthetics initiates protection against ischemic injury. Despite the role of the mBK in cardioprotection, the molecular identity of the channel remains unknown. We investigated the attributes of the mBK using C. elegans and mouse genetic models coupled with measurements of mitochondrial K(+) transport and APC. The canonical Ca(2+)-activated BK (or "maxi-K") channel SLO1 was dispensable for both mitochondrial K(+) transport and APC in both organisms. Instead, we found that the related but physiologically-distinct K(+) channel SLO2 was required, and that SLO2-dependent mitochondrial K(+) transport was triggered directly by volatile anesthetics. In addition, a SLO2 channel activator mimicked the protective effects of volatile anesthetics. These findings suggest that SLO2 contributes to protection from hypoxic injury by increasing the permeability of the mitochondrial inner membrane to K(+).
Collapse
Affiliation(s)
- Andrew P. Wojtovich
- Department of Medicine, University of Rochester Medical Center, Rochester, New York, United States of America
| | - Teresa A. Sherman
- Department of Medicine, University of Rochester Medical Center, Rochester, New York, United States of America
| | - Sergiy M. Nadtochiy
- Department of Anesthesiology, University of Rochester Medical Center, Rochester, New York, United States of America
| | - William R. Urciuoli
- Department of Anesthesiology, University of Rochester Medical Center, Rochester, New York, United States of America
| | - Paul S. Brookes
- Department of Anesthesiology, University of Rochester Medical Center, Rochester, New York, United States of America
- Department of Pharmacology and Physiology, University of Rochester Medical Center, Rochester, New York, United States of America
| | - Keith Nehrke
- Department of Medicine, University of Rochester Medical Center, Rochester, New York, United States of America
- Department of Pharmacology and Physiology, University of Rochester Medical Center, Rochester, New York, United States of America
- * E-mail:
| |
Collapse
|
25
|
Cysteine scanning and modification reveal major differences between BK channels and Kv channels in the inner pore region. Proc Natl Acad Sci U S A 2011; 108:12161-6. [PMID: 21730134 DOI: 10.1073/pnas.1104150108] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
BK channels are regulated by two distinct physiological signals, transmembrane potential and intracellular Ca(2+), each acting through independent modular sensor domains. However, despite a presumably central role in the coupling of sensor activation to channel gating, the pore-lining S6 transmembrane segment has not been systematically studied. Here, cysteine substitution and modification studies of the BK S6 point to substantial differences between BK and Kv channels in the structure and function of the S6-lined inner pore. Gating shifts caused by introduction of cysteines define a pattern and direction of free energy changes in BK S6 distinct from Shaker. Modification of BK S6 residues identifies pore-facing residues that occur at different linear positions along aligned BK and Kv S6 segments. Periodicity analysis suggests that one factor contributing to these differences may be a disruption of the BK S6 α-helix from the unique diglycine motif at the position of the Kv hinge glycine. State-dependent MTS accessibility reveals that, even in closed states, modification can occur. Furthermore, the inner pore of BK channels is much larger than that of K(+) channels with solved crystal structures. The results suggest caution in the use of Kv channel structures as templates for BK homology models, at least in the pore-gate domain.
Collapse
|
26
|
Imlach WL, Finch SC, Zhang Y, Dunlop J, Dalziel JE. Mechanism of action of lolitrem B, a fungal endophyte derived toxin that inhibits BK large conductance Ca²+-activated K+ channels. Toxicon 2011; 57:686-94. [PMID: 21300077 DOI: 10.1016/j.toxicon.2011.01.013] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2010] [Revised: 01/22/2011] [Accepted: 01/24/2011] [Indexed: 12/18/2022]
Abstract
The aim of this study was to compare the mode of action of the commonly used BK inhibitor paxilline with that of the more recently discovered lolitrem B. Similarities and differences in characteristics of inhibition between the two compounds were investigated. We have previously shown that lolitrem B does not affect the BK channel G-V, in contrast to the rightward shift produced by paxilline. These different effects on the voltage-dependence of activation suggest different modes of action for these two compounds. In this study we show that inhibition by both paxilline and lolitrem B is characterized by an open state preference for BK (hSlo) channels. Both compounds had a 3-fold higher apparent affinity under conditions likely to favour the open state, suggesting they have a similar BK conformational preference for binding. Furthermore, both compounds had a calcium concentration-dependence to their inhibitory effects. The G-V shift induced by paxilline was calcium concentration-dependent.
Collapse
Affiliation(s)
- Wendy L Imlach
- AgResearch, Grasslands Research Centre, Private Bag 11008, Palmerston North 4442, New Zealand
| | | | | | | | | |
Collapse
|