1
|
Sancho M, Klug NR, Harraz OF, Hill-Eubanks D, Nelson MT. Distinct potassium channel types in brain capillary pericytes. Biophys J 2024; 123:2110-2121. [PMID: 38444160 PMCID: PMC11309962 DOI: 10.1016/j.bpj.2024.03.004] [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: 11/15/2023] [Revised: 01/25/2024] [Accepted: 03/01/2024] [Indexed: 03/07/2024] Open
Abstract
Capillaries, composed of electrically coupled endothelial cells and overlying pericytes, constitute the vast majority of blood vessels in the brain. The most arteriole-proximate three to four branches of the capillary bed are covered by α-actin-expressing, contractile pericytes. These mural cells have a distinctive morphology and express different markers compared with their smooth muscle cell (SMC) cousins but share similar excitation-coupling contraction machinery. Despite this similarity, pericytes are considerably more depolarized than SMCs at low intravascular pressures. We have recently shown that pericytes, such as SMCs, possess functional voltage-dependent Ca2+ channels and ATP-sensitive K+ channels. Here, we further investigate the complement of pericyte ion channels, focusing on members of the K+ channel superfamily. Using NG2-DsRed-transgenic mice and diverse configurations of the patch-clamp technique, we demonstrate that pericytes display robust inward-rectifier K+ currents that are primarily mediated by the Kir2 family, based on their unique biophysical characteristics and sensitivity to micromolar concentrations of Ba2+. Moreover, multiple lines of evidence, including characteristic kinetics, sensitivity to specific blockers, biophysical attributes, and distinctive single-channel properties, established the functional expression of two voltage-dependent K+ channels: KV1 and BKCa. Although these three types of channels are also present in SMCs, they exhibit distinctive current density and kinetics profiles in pericytes. Collectively, these findings underscore differences in the operation of shared molecular features between pericytes and SMCs and highlight the potential contribution of these three K+ ion channels in setting pericyte membrane potential, modulating capillary hemodynamics, and regulating cerebral blood flow.
Collapse
Affiliation(s)
- Maria Sancho
- Department of Pharmacology, University of Vermont, Burlington, Vermont; Department of Physiology, Faculty of Medicine, Complutense University of Madrid, Madrid, Spain.
| | - Nicholas R Klug
- Department of Pharmacology, University of Vermont, Burlington, Vermont
| | - Osama F Harraz
- Department of Pharmacology, University of Vermont, Burlington, Vermont; Vermont Center for Cardiovascular and Brain Health, Larner College of Medicine, University of Vermont, Burlington, Vermont
| | | | - Mark T Nelson
- Department of Pharmacology, University of Vermont, Burlington, Vermont; Vermont Center for Cardiovascular and Brain Health, Larner College of Medicine, University of Vermont, Burlington, Vermont; Division of Cardiovascular Sciences, University of Manchester, Manchester, United Kingdom.
| |
Collapse
|
2
|
Fernández Santoro EM, Karim A, Warnaar P, De Zeeuw CI, Badura A, Negrello M. Purkinje cell models: past, present and future. Front Comput Neurosci 2024; 18:1426653. [PMID: 39049990 PMCID: PMC11266113 DOI: 10.3389/fncom.2024.1426653] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2024] [Accepted: 06/24/2024] [Indexed: 07/27/2024] Open
Abstract
The investigation of the dynamics of Purkinje cell (PC) activity is crucial to unravel the role of the cerebellum in motor control, learning and cognitive processes. Within the cerebellar cortex (CC), these neurons receive all the incoming sensory and motor information, transform it and generate the entire cerebellar output. The relatively homogenous and repetitive structure of the CC, common to all vertebrate species, suggests a single computation mechanism shared across all PCs. While PC models have been developed since the 70's, a comprehensive review of contemporary models is currently lacking. Here, we provide an overview of PC models, ranging from the ones focused on single cell intracellular PC dynamics, through complex models which include synaptic and extrasynaptic inputs. We review how PC models can reproduce physiological activity of the neuron, including firing patterns, current and multistable dynamics, plateau potentials, calcium signaling, intrinsic and synaptic plasticity and input/output computations. We consider models focusing both on somatic and on dendritic computations. Our review provides a critical performance analysis of PC models with respect to known physiological data. We expect our synthesis to be useful in guiding future development of computational models that capture real-life PC dynamics in the context of cerebellar computations.
Collapse
Affiliation(s)
| | - Arun Karim
- Department of Neuroscience, Erasmus MC, Rotterdam, Netherlands
| | - Pascal Warnaar
- Department of Neuroscience, Erasmus MC, Rotterdam, Netherlands
- Netherlands Institute for Neuroscience, Royal Academy of Arts and Sciences, Amsterdam, Netherlands
| | - Chris I. De Zeeuw
- Department of Neuroscience, Erasmus MC, Rotterdam, Netherlands
- Netherlands Institute for Neuroscience, Royal Academy of Arts and Sciences, Amsterdam, Netherlands
| | | | - Mario Negrello
- Department of Neuroscience, Erasmus MC, Rotterdam, Netherlands
| |
Collapse
|
3
|
Fedida D, Sastre D, Dou Y, Westhoff M, Eldstrom J. Evaluating sequential and allosteric activation models in IKs channels with mutated voltage sensors. J Gen Physiol 2024; 156:e202313465. [PMID: 38294435 PMCID: PMC10829594 DOI: 10.1085/jgp.202313465] [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: 08/16/2023] [Revised: 11/30/2023] [Accepted: 01/03/2024] [Indexed: 02/01/2024] Open
Abstract
The ion-conducting IKs channel complex, important in cardiac repolarization and arrhythmias, comprises tetramers of KCNQ1 α-subunits along with 1-4 KCNE1 accessory subunits and calmodulin regulatory molecules. The E160R mutation in individual KCNQ1 subunits was used to prevent activation of voltage sensors and allow direct determination of transition rate data from complexes opening with a fixed number of 1, 2, or 4 activatable voltage sensors. Markov models were used to test the suitability of sequential versus allosteric models of IKs activation by comparing simulations with experimental steady-state and transient activation kinetics, voltage-sensor fluorescence from channels with two or four activatable domains, and limiting slope currents at negative potentials. Sequential Hodgkin-Huxley-type models approximately describe IKs currents but cannot explain an activation delay in channels with only one activatable subunit or the hyperpolarizing shift in the conductance-voltage relationship with more activatable voltage sensors. Incorporating two voltage sensor activation steps in sequential models and a concerted step in opening via rates derived from fluorescence measurements improves models but does not resolve fundamental differences with experimental data. Limiting slope current data that show the opening of channels at negative potentials and very low open probability are better simulated using allosteric models of activation with one transition per voltage sensor, which implies that movement of all four sensors is not required for IKs conductance. Tiered allosteric models with two activating transitions per voltage sensor can fully account for IKs current and fluorescence activation kinetics in constructs with different numbers of activatable voltage sensors.
Collapse
Affiliation(s)
- David Fedida
- Department of Anesthesiology, Pharmacology and Therapeutics, University of British Columbia, Vancouver, Canada
| | - Daniel Sastre
- Department of Anesthesiology, Pharmacology and Therapeutics, University of British Columbia, Vancouver, Canada
| | - Ying Dou
- Department of Anesthesiology, Pharmacology and Therapeutics, University of British Columbia, Vancouver, Canada
| | - Maartje Westhoff
- Department of Anesthesiology, Pharmacology and Therapeutics, University of British Columbia, Vancouver, Canada
| | - Jodene Eldstrom
- Department of Anesthesiology, Pharmacology and Therapeutics, University of British Columbia, Vancouver, Canada
| |
Collapse
|
4
|
Gao J, Yin H, Dong Y, Wang X, Liu Y, Wang K. A Novel Role of Uricosuric Agent Benzbromarone in BK Channel Activation and Reduction of Airway Smooth Muscle Contraction. Mol Pharmacol 2023; 103:241-254. [PMID: 36669879 DOI: 10.1124/molpharm.122.000638] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2022] [Revised: 11/28/2022] [Accepted: 12/19/2022] [Indexed: 01/21/2023] Open
Abstract
The uricosuric drug benzbromarone, widely used for treatment of gout, hyperpolarizes the membrane potential of airway smooth muscle cells, but how it works remains unknown. Here we show a novel role of benzbromarone in activation of large conductance calcium-activated K+ channels. Benzbromarone results in dose-dependent activation of macroscopic big potassium (BK) currents about 1.7- to 14.5-fold with an EC50 of 111 μM and shifts the voltage-dependent channel activation to a more hyperpolarizing direction about 10 to 54 mV in whole-cell patch clamp recordings. In single-channel recordings, benzbromarone decreases single BKα channel closed dwell time and increases the channel open probability. Coexpressing β1 subunit also enhances BK activation by benzbromarone with an EC50 of 67 μM and a leftward shift of conductance-voltage (G-V) curve about 44 to 138 mV. Site-directed mutagenesis reveals that a motif of three amino acids 329RKK331 in the cytoplasmic linker between S6 and C-terminal regulator of potassium conductance (RCK) gating ring mediates the pharmacological activation of BK channels by benzbromarone. Further ex vivo assay shows that benzbromarone causes reduction of tracheal strip contraction. Taken together, our findings demonstrate that uricosuric benzbromarone activates BK channels through molecular mechanism of action involving the channel RKK motif of S6-RCK linker. Pharmacological activation of BK channel by benzbromarone causes reduction of tracheal strip contraction, holding a repurposing potential for asthma and pulmonary arterial hypertension or BK channelopathies. SIGNIFICANCE STATEMENT: We describe a novel role of uricosuric agent benzbromarone in big potassium (BK) channel activation and relaxation of airway smooth muscle contraction. In this study, we find that benzbromarone is an activator of the large-conductance Ca2+- and voltage-activated K+ channel (BK channel), which serves numerous cellular functions, including control of smooth muscle contraction. Pharmacological activation of BK channel by the FDA-approved drug benzbromarone may hold repurposing potential for treatment of asthma and pulmonary arterial hypertension or BK channelopathies.
Collapse
Affiliation(s)
- Jian Gao
- Department of Pharmacology, School of Pharmaceutical Sciences, Peking University, Beijing, China (J.G., X.W.); Department of Pharmacology, School of Pharmacy, Qingdao University Medical College, Qingdao, China (H.Y., Y.D., Y.L., K.W.); and Institute of Innovative Drugs, Qingdao University, Qingdao, China (Y.L., K.W.)
| | - Hao Yin
- Department of Pharmacology, School of Pharmaceutical Sciences, Peking University, Beijing, China (J.G., X.W.); Department of Pharmacology, School of Pharmacy, Qingdao University Medical College, Qingdao, China (H.Y., Y.D., Y.L., K.W.); and Institute of Innovative Drugs, Qingdao University, Qingdao, China (Y.L., K.W.)
| | - Yanqun Dong
- Department of Pharmacology, School of Pharmaceutical Sciences, Peking University, Beijing, China (J.G., X.W.); Department of Pharmacology, School of Pharmacy, Qingdao University Medical College, Qingdao, China (H.Y., Y.D., Y.L., K.W.); and Institute of Innovative Drugs, Qingdao University, Qingdao, China (Y.L., K.W.)
| | - Xintong Wang
- Department of Pharmacology, School of Pharmaceutical Sciences, Peking University, Beijing, China (J.G., X.W.); Department of Pharmacology, School of Pharmacy, Qingdao University Medical College, Qingdao, China (H.Y., Y.D., Y.L., K.W.); and Institute of Innovative Drugs, Qingdao University, Qingdao, China (Y.L., K.W.)
| | - Yani Liu
- Department of Pharmacology, School of Pharmaceutical Sciences, Peking University, Beijing, China (J.G., X.W.); Department of Pharmacology, School of Pharmacy, Qingdao University Medical College, Qingdao, China (H.Y., Y.D., Y.L., K.W.); and Institute of Innovative Drugs, Qingdao University, Qingdao, China (Y.L., K.W.)
| | - KeWei Wang
- Department of Pharmacology, School of Pharmaceutical Sciences, Peking University, Beijing, China (J.G., X.W.); Department of Pharmacology, School of Pharmacy, Qingdao University Medical College, Qingdao, China (H.Y., Y.D., Y.L., K.W.); and Institute of Innovative Drugs, Qingdao University, Qingdao, China (Y.L., K.W.)
| |
Collapse
|
5
|
Sun L, Horrigan FT. A gating lever and molecular logic gate that couple voltage and calcium sensor activation to opening in BK potassium channels. SCIENCE ADVANCES 2022; 8:eabq5772. [PMID: 36516264 PMCID: PMC9750137 DOI: 10.1126/sciadv.abq5772] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/18/2022] [Accepted: 11/08/2022] [Indexed: 06/17/2023]
Abstract
BK channels uniquely integrate voltage and calcium signaling in diverse cell types through allosteric activation of their K+-conducting pore by structurally distinct V and Ca2+ sensor domains. Here, we define mechanisms and interaction pathways that link V sensors to the pore by analyzing effects on allosteric coupling of point mutations in the context of Slo1 BK channel structure. A gating lever, mediated by S4/S5 segment interaction within the transmembrane domain, rotates to engage and stabilize the open conformation of the S6 inner pore helix upon V sensor activation. In addition, an indirect pathway, mediated by the carboxyl-terminal cytosolic domain (CTD) and C-linker that connects the CTD to S6, stabilizes the closed conformation when V sensors are at rest. Unexpectedly, this mechanism, which bypasses the covalent connections of C-linker to CTD and pore, also transduces Ca2+-dependent coupling in a manner that is completely nonadditive with voltage, analogous to the function of a digital logic (OR) gate.
Collapse
Affiliation(s)
- Liang Sun
- Department of Integrative Physiology, Baylor College of Medicine, Houston, TX 77030, USA
| | - Frank T. Horrigan
- Department of Integrative Physiology, Baylor College of Medicine, Houston, TX 77030, USA
| |
Collapse
|
6
|
Zhang G, Xu X, Jia Z, Geng Y, Liang H, Shi J, Marras M, Abella C, Magleby KL, Silva JR, Chen J, Zou X, Cui J. An allosteric modulator activates BK channels by perturbing coupling between Ca 2+ binding and pore opening. Nat Commun 2022; 13:6784. [PMID: 36351900 PMCID: PMC9646747 DOI: 10.1038/s41467-022-34359-6] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2022] [Accepted: 10/21/2022] [Indexed: 11/10/2022] Open
Abstract
BK type Ca2+-activated K+ channels activate in response to both voltage and Ca2+. The membrane-spanning voltage sensor domain (VSD) activation and Ca2+ binding to the cytosolic tail domain (CTD) open the pore across the membrane, but the mechanisms that couple VSD activation and Ca2+ binding to pore opening are not clear. Here we show that a compound, BC5, identified from in silico screening, interacts with the CTD-VSD interface and specifically modulates the Ca2+ dependent activation mechanism. BC5 activates the channel in the absence of Ca2+ binding but Ca2+ binding inhibits BC5 effects. Thus, BC5 perturbs a pathway that couples Ca2+ binding to pore opening to allosterically affect both, which is further supported by atomistic simulations and mutagenesis. The results suggest that the CTD-VSD interaction makes a major contribution to the mechanism of Ca2+ dependent activation and is an important site for allosteric agonists to modulate BK channel activation.
Collapse
Affiliation(s)
- Guohui Zhang
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University, St. Louis, MO, USA
| | - Xianjin Xu
- Dalton Cardiovascular Research Center, University of Missouri - Columbia, Columbia, MO, USA.,Department of Physics and Astronomy, University of Missouri - Columbia, Columbia, MO, USA.,Department of Biochemistry, University of Missouri - Columbia, Columbia, MO, USA.,Institute for Data Science and Informatics, University of Missouri - Columbia, Columbia, MO, USA
| | - Zhiguang Jia
- Department of Chemistry, University of Massachusetts, Amherst, MA, USA.,Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, MA, USA
| | - Yanyan Geng
- Department of Physiology and Biophysics, University of Miami Miller School of Medicine, Miami, FL, USA
| | - Hongwu Liang
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University, St. Louis, MO, USA
| | - Jingyi Shi
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University, St. Louis, MO, USA
| | - Martina Marras
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University, St. Louis, MO, USA
| | - Carlota Abella
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University, St. Louis, MO, USA
| | - Karl L Magleby
- Department of Physiology and Biophysics, University of Miami Miller School of Medicine, Miami, FL, USA
| | - Jonathan R Silva
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University, St. Louis, MO, USA.
| | - Jianhan Chen
- Department of Chemistry, University of Massachusetts, Amherst, MA, USA. .,Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, MA, USA.
| | - Xiaoqin Zou
- Dalton Cardiovascular Research Center, University of Missouri - Columbia, Columbia, MO, USA. .,Department of Physics and Astronomy, University of Missouri - Columbia, Columbia, MO, USA. .,Department of Biochemistry, University of Missouri - Columbia, Columbia, MO, USA. .,Institute for Data Science and Informatics, University of Missouri - Columbia, Columbia, MO, USA.
| | - Jianmin Cui
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University, St. Louis, MO, USA.
| |
Collapse
|
7
|
To what extent naringenin binding and membrane depolarization shape mitoBK channel gating—A machine learning approach. PLoS Comput Biol 2022; 18:e1010315. [PMID: 35857767 PMCID: PMC9342765 DOI: 10.1371/journal.pcbi.1010315] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2021] [Revised: 08/01/2022] [Accepted: 06/16/2022] [Indexed: 11/19/2022] Open
Abstract
The large conductance voltage- and Ca2+-activated K+ channels from the inner mitochondrial membrane (mitoBK) are modulated by a number of factors. Among them flavanones, including naringenin (Nar), arise as a promising group of mitoBK channel regulators from a pharmacological point of view. It is well known that in the presence of Nar the open state probability (pop) of mitoBK channels significantly increases. Nevertheless, the molecular mechanism of the mitoBK-Nar interactions remains still unrevealed. It is also not known whether the effects of naringenin administration on conformational dynamics can resemble those which are exerted by the other channel-activating stimuli. In aim to answer this question, we examine whether the dwell-time series of mitoBK channels which were obtained at different voltages and Nar concentrations (yet allowing to reach comparable pops) are discernible by means of artificial intelligence methods, including k-NN and shapelet learning. The obtained results suggest that the structural complexity of the gating dynamics is shaped both by the interaction of channel gate with the voltage sensor (VSD) and the Nar-binding site. For a majority of data one can observe stimulus-specific patterns of channel gating. Shapelet algorithm allows to obtain better prediction accuracy in most cases. Probably, because it takes into account the complexity of local features of a given signal. About 30% of the analyzed time series do not sufficiently differ to unambiguously distinguish them from each other, which can be interpreted in terms of the existence of the common features of mitoBK channel gating regardless of the type of activating stimulus. There exist long-range mutual interactions between VSD and the Nar-coordination site that are responsible for higher levels of Nar-activation (Δpop) at deeply depolarized membranes. These intra-sensor interactions are anticipated to have an allosteric nature.
Collapse
|
8
|
Guan F, Li T, Dong W, Guo R, Chai H, Chen Z, Ren Z, Li Y, Ye S. Novel insights into the allosteric gating mechanism of MthK channel. Natl Sci Rev 2022; 9:nwac072. [PMID: 36072506 PMCID: PMC9440719 DOI: 10.1093/nsr/nwac072] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2021] [Revised: 02/28/2022] [Accepted: 03/29/2022] [Indexed: 11/29/2022] Open
Abstract
Allostery is a fundamental element during channel gating in response to an appropriate stimulus by which events occurring at one site are transmitted to distal sites to regulate activity. To address how binding of the first Ca2+ ion at one of the eight chemically identical subunits facilitates the other Ca2+-binding events in MthK, a Ca2+-gated K+ channel containing a conserved ligand-binding RCK domain, we analysed a large collection of MthK structures and performed the corresponding thermodynamic and electrophysiological measurements. These structural and functional studies led us to conclude that the conformations of the Ca2+-binding sites alternate between two quaternary states and exhibit significant differences in Ca2+ affinity. We further propose an allosteric model of the MthK-gating mechanism by which a cascade of structural events connect the initial Ca2+-binding to the final changes of the ring structure that open the ion-conduction pore. This mechanical model reveals the exquisite design that achieves the allosteric gating and could be of general relevance for the action of other ligand-gated ion channels containing the RCK domain.
Collapse
Affiliation(s)
- Fenghui Guan
- Frontiers Science Center for Synthetic Biology (Ministry of Education), Tianjin Key Laboratory of Function and Application of Biological Macromolecular Structures, School of Life Sciences, Tianjin University, 92 Weijin Road, Nankai District, Tianjin300072, China
- The Cancer Hospital of the University of Chinese Academy of Sciences, Institute of Basic Medicine and Cancer (IBMC), Chinese Academy of Sciences, Hangzhou, Zhejiang310022, China
| | - Tianyu Li
- State Key Laboratory of Drug Research and Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai201203, China
- University of Chinese Academy of Sciences, No. 19A Yuquan Road, Beijing100049, China
| | - Wei Dong
- Life Sciences Institute, Zhejiang University, Hangzhou, 310058Zhejiang, China
| | - Rui Guo
- Department of Logistics, Tianjin University, 92 Weijin Road, Nankai District, Tianjin300072, China
| | - Hao Chai
- State Key Laboratory of Drug Research and Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai201203, China
- University of Chinese Academy of Sciences, No. 19A Yuquan Road, Beijing100049, China
| | - Zhiqiu Chen
- University of Chinese Academy of Sciences, No. 19A Yuquan Road, Beijing100049, China
| | - Zhong Ren
- Department of Chemistry, University of Illinois at Chicago, Chicago, IL60607, USA
- Renz Research Inc., Westmont, IL60559, USA
| | - Yang Li
- State Key Laboratory of Drug Research and Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai201203, China
- University of Chinese Academy of Sciences, No. 19A Yuquan Road, Beijing100049, China
- National Clinical Research Center for Aging and Medicine, Huashan Hospital, Fudan University, China
| | - Sheng Ye
- Frontiers Science Center for Synthetic Biology (Ministry of Education), Tianjin Key Laboratory of Function and Application of Biological Macromolecular Structures, School of Life Sciences, Tianjin University, 92 Weijin Road, Nankai District, Tianjin300072, China
- Life Sciences Institute, Zhejiang University, Hangzhou, 310058Zhejiang, China
| |
Collapse
|
9
|
González-Cota AL, Santana-Calvo C, Servín-Vences R, Orta G, Balderas E. Regulatory mechanisms of mitochondrial BK Ca channels. Channels (Austin) 2021; 15:424-437. [PMID: 33955332 PMCID: PMC8117780 DOI: 10.1080/19336950.2021.1919463] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2021] [Revised: 04/05/2021] [Accepted: 04/05/2021] [Indexed: 02/06/2023] Open
Abstract
The mitochondrial BKCa channel (mitoBKCa) is a splice variant of plasma membrane BKCa (Maxi-K, BKCa, Slo1, KCa1.1). While a high-resolution structure of mitoBKCa is not available yet, functional and structural studies of the plasma membrane BKCa have provided important clues on the gating of the channel by voltage and Ca2+, as well as the interaction with auxiliary subunits. To date, we know that the control of expression of mitoBKCa, targeting and voltage-sensitivity strongly depends on its association with its regulatory β1-subunit, which overall participate in the control of mitochondrial Ca2+-overload in cardiac myocytes. Moreover, novel regulatory mechanisms of mitoBKCa such as β-subunits and amyloid-β have recently been proposed. However, major basic questions including how the regulatory BKCa-β1-subunit reaches mitochondria and the mechanism through which amyloid-β impairs mitoBKCa channel function remain to be addressed.
Collapse
Affiliation(s)
- Ana L. González-Cota
- Departamento de Genética del Desarrollo y Fisiología Molecular, Instituto de Biotecnología, UNAM. Av. Universidad 2001, Cuernavaca, Morelos, México
| | - Carmen Santana-Calvo
- Instituto Gulbenkian de Ciência. Rua da Quinta Grande 6, Oeiras, Portugal
- Instituto de Tecnologia Química e Biológica, Universida de Nova de Lisboa. Av. da República, Oeiras, Portugal
| | - Rocío Servín-Vences
- Department of Neuroscience, The Scripps Research Institute. 10550 North Torrey Pines Road, La Jolla, CA, USA
| | - Gerardo Orta
- Departamento de Genética del Desarrollo y Fisiología Molecular, Instituto de Biotecnología, UNAM. Av. Universidad 2001, Cuernavaca, Morelos, México
| | - Enrique Balderas
- Nora Eccles Harrison Cardiovascular Research & Training Institute, University of Utah, Salt Lake City, UT, USA
| |
Collapse
|
10
|
Priest MF, Lee EE, Bezanilla F. Tracking the movement of discrete gating charges in a voltage-gated potassium channel. eLife 2021; 10:58148. [PMID: 34779404 PMCID: PMC8635975 DOI: 10.7554/elife.58148] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2020] [Accepted: 11/08/2021] [Indexed: 01/18/2023] Open
Abstract
Positively charged amino acids respond to membrane potential changes to drive voltage sensor movement in voltage-gated ion channels, but determining the displacements of voltage sensor gating charges has proven difficult. We optically tracked the movement of the two most extracellular charged residues (R1 and R2) in the Shaker potassium channel voltage sensor using a fluorescent positively charged bimane derivative (qBBr) that is strongly quenched by tryptophan. By individually mutating residues to tryptophan within the putative pathway of gating charges, we observed that the charge motion during activation is a rotation and a tilted translation that differs between R1 and R2. Tryptophan-induced quenching of qBBr also indicates that a crucial residue of the hydrophobic plug is linked to the Cole-Moore shift through its interaction with R1. Finally, we show that this approach extends to additional voltage-sensing membrane proteins using the Ciona intestinalis voltage-sensitive phosphatase (CiVSP).
Collapse
Affiliation(s)
- Michael F Priest
- Committee on Neurobiology and Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, United States
| | - Elizabeth El Lee
- Committee on Neurobiology and Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, United States
| | - Francisco Bezanilla
- Committee on Neurobiology and Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, United States.,Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, United States
| |
Collapse
|
11
|
Sancho M, Kyle BD. The Large-Conductance, Calcium-Activated Potassium Channel: A Big Key Regulator of Cell Physiology. Front Physiol 2021; 12:750615. [PMID: 34744788 PMCID: PMC8567177 DOI: 10.3389/fphys.2021.750615] [Citation(s) in RCA: 27] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2021] [Accepted: 09/29/2021] [Indexed: 12/01/2022] Open
Abstract
Large-conductance Ca2+-activated K+ channels facilitate the efflux of K+ ions from a variety of cells and tissues following channel activation. It is now recognized that BK channels undergo a wide range of pre- and post-translational modifications that can dramatically alter their properties and function. This has downstream consequences in affecting cell and tissue excitability, and therefore, function. While finding the “silver bullet” in terms of clinical therapy has remained elusive, ongoing research is providing an impressive range of viable candidate proteins and mechanisms that associate with and modulate BK channel activity, respectively. Here, we provide the hallmarks of BK channel structure and function generally, and discuss important milestones in the efforts to further elucidate the diverse properties of BK channels in its many forms.
Collapse
Affiliation(s)
- Maria Sancho
- Department of Pharmacology, University of Vermont, Burlington, VT, United States
| | - Barry D Kyle
- Department of Pathology and Laboratory Medicine, College of Medicine, University of Saskatchewan, Saskatoon, SK, Canada
| |
Collapse
|
12
|
Cui J. BK Channel Gating Mechanisms: Progresses Toward a Better Understanding of Variants Linked Neurological Diseases. Front Physiol 2021; 12:762175. [PMID: 34744799 PMCID: PMC8567085 DOI: 10.3389/fphys.2021.762175] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2021] [Accepted: 10/01/2021] [Indexed: 12/21/2022] Open
Abstract
The large conductance Ca2+-activated potassium (BK) channel is activated by both membrane potential depolarization and intracellular Ca2+ with distinct mechanisms. Neural physiology is sensitive to the function of BK channels, which is shown by the discoveries of neurological disorders that are associated with BK channel mutations. This article reviews the molecular mechanisms of BK channel activation in response to voltage and Ca2+ binding, including the recent progress since the publication of the atomistic structure of the whole BK channel protein, and the neurological disorders associated with BK channel mutations. These results demonstrate the unique mechanisms of BK channel activation and that these mechanisms are important factors in linking BK channel mutations to neurological disorders.
Collapse
Affiliation(s)
- Jianmin Cui
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University, St. Louis, MO, United States
| |
Collapse
|
13
|
Lu T, Lee HC. Coronary Large Conductance Ca 2+-Activated K + Channel Dysfunction in Diabetes Mellitus. Front Physiol 2021; 12:750618. [PMID: 34744789 PMCID: PMC8567020 DOI: 10.3389/fphys.2021.750618] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2021] [Accepted: 09/14/2021] [Indexed: 11/24/2022] Open
Abstract
Diabetes mellitus (DM) is an independent risk of macrovascular and microvascular complications, while cardiovascular diseases remain a leading cause of death in both men and women with diabetes. Large conductance Ca2+-activated K+ (BK) channels are abundantly expressed in arteries and are the key ionic determinant of vascular tone and organ perfusion. It is well established that the downregulation of vascular BK channel function with reduced BK channel protein expression and altered intrinsic BK channel biophysical properties is associated with diabetic vasculopathy. Recent efforts also showed that diabetes-associated changes in signaling pathways and transcriptional factors contribute to the downregulation of BK channel expression. This manuscript will review our current understandings on the molecular, physiological, and biophysical mechanisms that underlie coronary BK channelopathy in diabetes mellitus.
Collapse
Affiliation(s)
- Tong Lu
- Department of Cardiovascular Medicine, Mayo Clinic, Rochester, MN, United States
| | - Hon-Chi Lee
- Department of Cardiovascular Medicine, Mayo Clinic, Rochester, MN, United States
| |
Collapse
|
14
|
Rockman ME, Vouga AG, Rothberg BS. Molecular mechanism of BK channel activation by the smooth muscle relaxant NS11021. J Gen Physiol 2021; 152:151593. [PMID: 32221543 PMCID: PMC7266150 DOI: 10.1085/jgp.201912506] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2019] [Accepted: 02/12/2020] [Indexed: 12/31/2022] Open
Abstract
Large-conductance Ca2+-activated K+ channels (BK channels) are activated by cytosolic calcium and depolarized membrane potential under physiological conditions. Thus, these channels control electrical excitability in neurons and smooth muscle by gating K+ efflux and hyperpolarizing the membrane in response to Ca2+ signaling. Altered BK channel function has been linked to epilepsy, dyskinesia, and other neurological deficits in humans, making these channels a key target for drug therapies. To gain insight into mechanisms underlying pharmacological modulation of BK channel gating, here we studied mechanisms underlying activation of BK channels by the biarylthiourea derivative, NS11021, which acts as a smooth muscle relaxant. We observe that increasing NS11021 shifts the half-maximal activation voltage for BK channels toward more hyperpolarized voltages, in both the presence and nominal absence of Ca2+, suggesting that NS11021 facilitates BK channel activation primarily by a mechanism that is distinct from Ca2+ activation. 30 µM NS11021 slows the time course of BK channel deactivation at −200 mV by ∼10-fold compared with 0 µM NS11021, while having little effect on the time course of activation. This action is most pronounced at negative voltages, at which the BK channel voltage sensors are at rest. Single-channel kinetic analysis further shows that 30 µM NS11021 increases open probability by 62-fold and increases mean open time from 0.15 to 0.52 ms in the nominal absence of Ca2+ at voltages less than −60 mV, conditions in which BK voltage sensors are largely in the resting state. We could therefore account for the major activating effects of NS11021 by a scheme in which the drug primarily shifts the pore-gate equilibrium toward the open state.
Collapse
Affiliation(s)
- Michael E Rockman
- Department of Medical Genetics and Molecular Biochemistry, Temple University Lewis Katz School of Medicine, Philadelphia, PA
| | - Alexandre G Vouga
- Department of Medical Genetics and Molecular Biochemistry, Temple University Lewis Katz School of Medicine, Philadelphia, PA
| | - Brad S Rothberg
- Department of Medical Genetics and Molecular Biochemistry, Temple University Lewis Katz School of Medicine, Philadelphia, PA
| |
Collapse
|
15
|
Goblet cell LRRC26 regulates BK channel activation and protects against colitis in mice. Proc Natl Acad Sci U S A 2021; 118:2019149118. [PMID: 33431687 DOI: 10.1073/pnas.2019149118] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Goblet cells (GCs) are specialized cells of the intestinal epithelium contributing critically to mucosal homeostasis. One of the functions of GCs is to produce and secrete MUC2, the mucin that forms the scaffold of the intestinal mucus layer coating the epithelium and separates the luminal pathogens and commensal microbiota from the host tissues. Although a variety of ion channels and transporters are thought to impact on MUC2 secretion, the specific cellular mechanisms that regulate GC function remain incompletely understood. Previously, we demonstrated that leucine-rich repeat-containing protein 26 (LRRC26), a known regulatory subunit of the Ca2+-and voltage-activated K+ channel (BK channel), localizes specifically to secretory cells within the intestinal tract. Here, utilizing a mouse model in which MUC2 is fluorescently tagged, thereby allowing visualization of single GCs in intact colonic crypts, we show that murine colonic GCs have functional LRRC26-associated BK channels. In the absence of LRRC26, BK channels are present in GCs, but are not activated at physiological conditions. In contrast, all tested MUC2- cells completely lacked BK channels. Moreover, LRRC26-associated BK channels underlie the BK channel contribution to the resting transepithelial current across mouse distal colonic mucosa. Genetic ablation of either LRRC26 or BK pore-forming α-subunit in mice results in a dramatically enhanced susceptibility to colitis induced by dextran sodium sulfate. These results demonstrate that normal potassium flux through LRRC26-associated BK channels in GCs has protective effects against colitis in mice.
Collapse
|
16
|
Ottolini M, Sonkusare SK. The Calcium Signaling Mechanisms in Arterial Smooth Muscle and Endothelial Cells. Compr Physiol 2021; 11:1831-1869. [PMID: 33792900 PMCID: PMC10388069 DOI: 10.1002/cphy.c200030] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The contractile state of resistance arteries and arterioles is a crucial determinant of blood pressure and blood flow. Physiological regulation of arterial contractility requires constant communication between endothelial and smooth muscle cells. Various Ca2+ signals and Ca2+ -sensitive targets ensure dynamic control of intercellular communications in the vascular wall. The functional effect of a Ca2+ signal on arterial contractility depends on the type of Ca2+ -sensitive target engaged by that signal. Recent studies using advanced imaging methods have identified the spatiotemporal signatures of individual Ca2+ signals that control arterial and arteriolar contractility. Broadly speaking, intracellular Ca2+ is increased by ion channels and transporters on the plasma membrane and endoplasmic reticular membrane. Physiological roles for many vascular Ca2+ signals have already been confirmed, while further investigation is needed for other Ca2+ signals. This article focuses on endothelial and smooth muscle Ca2+ signaling mechanisms in resistance arteries and arterioles. We discuss the Ca2+ entry pathways at the plasma membrane, Ca2+ release signals from the intracellular stores, the functional and physiological relevance of Ca2+ signals, and their regulatory mechanisms. Finally, we describe the contribution of abnormal endothelial and smooth muscle Ca2+ signals to the pathogenesis of vascular disorders. © 2021 American Physiological Society. Compr Physiol 11:1831-1869, 2021.
Collapse
Affiliation(s)
- Matteo Ottolini
- Department of Pharmacology, University of Virginia, Charlottesville, Virginia, USA
| | - Swapnil K Sonkusare
- Department of Pharmacology, University of Virginia, Charlottesville, Virginia, USA.,Department of Molecular Physiology & Biological Physics, University of Virginia, Charlottesville, Virginia, USA.,Robert M. Berne Cardiovascular Research Center, University of Virginia, Charlottesville, Virginia, USA
| |
Collapse
|
17
|
Abstract
Potassium channels are present in every living cell and essential to setting up a stable, non-zero transmembrane electrostatic potential which manifests the off-equilibrium livelihood of the cell. They are involved in other cellular activities and regulation, such as the controlled release of hormones, the activation of T-cells for immune response, the firing of action potential in muscle cells and neurons, etc. Pharmacological reagents targeting potassium channels are important for treating various human diseases linked to dysfunction of the channels. High-resolution structures of these channels are very useful tools for delineating the detailed chemical basis underlying channel functions and for structure-based design and optimization of their pharmacological and pharmaceutical agents. Structural studies of potassium channels have revolutionized biophysical understandings of key concepts in the field - ion selectivity, conduction, channel gating, and modulation, making them multi-modality targets of pharmacological regulation. In this chapter, I will select a few high-resolution structures to illustrate key structural insights, proposed allostery behind channel functions, disagreements still open to debate, and channel-lipid interactions and co-evolution. The known structural consensus allows the inference of conserved molecular mechanisms shared among subfamilies of K+ channels and makes it possible to develop channel-specific pharmaceutical agents.
Collapse
Affiliation(s)
- Qiu-Xing Jiang
- Laboratory of Molecular Physiology and Biophysics and the Cryo-EM Center, Hauptmann-Woodward Medical Research Institute, Buffalo, NY, USA.
- Department of Medicinal Chemistry, University of Florida, Gainesville, FL, USA.
- Departments of Materials Design and Invention and Physiology and Biophysics, University of Buffalo (SUNY), Buffalo, NY, USA.
| |
Collapse
|
18
|
Zhang G, Gibson RA, McDonald M, Liang P, Kang PW, Shi J, Yang H, Cui J, Mikati MA. A Gain-of-Function Mutation in KCNMA1 Causes Dystonia Spells Controlled With Stimulant Therapy. Mov Disord 2020; 35:1868-1873. [PMID: 32633875 DOI: 10.1002/mds.28138] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2020] [Revised: 05/08/2020] [Accepted: 05/15/2020] [Indexed: 12/11/2022] Open
Abstract
BACKGROUND The mutations of KCNMA1 BK-type K+ channel have been identified in patients with various movement disorders. The underlying pathophysiology and corresponding therapeutics are lacking. OBJECTIVES To report our clinical and biophysical characterizations of a novel de novo KCNMA1 variant, as well as an effective therapy for the patient's dystonia-atonia spells. METHODS Combination of phenotypic characterization, therapy, and biophysical characterization of the patient and her mutation. RESULTS The patient had >100 dystonia-atonia spells per day with mild cerebellar atrophy. She also had autism spectrum disorder, intellectual disability, and attention deficit hyperactivity disorder. Whole-exome sequencing identified a heterozygous de novo BK N536H mutation. Our biophysical characterization demonstrates that N536H is a gain-of-function mutation with markedly enhanced voltage-dependent activation. Remarkably, administration of dextroamphetamine completely suppressed the dystonia-atonia spells. CONCLUSIONS BK N536H is a gain-of-function that causes dystonia and other neurological symptoms. Our stimulant therapy opens a new avenue to mitigate KCNMA1-linked movement disorders. © 2020 International Parkinson and Movement Disorder Society.
Collapse
Affiliation(s)
- Guohui Zhang
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri, USA
| | - Rebecca A Gibson
- Department of Pediatrics, Duke University Medical Center, Durham, North Carolina, USA
| | - Marie McDonald
- Department of Pediatrics, Duke University Medical Center, Durham, North Carolina, USA
| | - Pengfei Liang
- Department of Biochemistry, Duke University Medical Center, Durham, North Carolina, USA
| | - Po Wei Kang
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri, USA
| | - Jingyi Shi
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri, USA
| | - Huanghe Yang
- Department of Biochemistry, Duke University Medical Center, Durham, North Carolina, USA.,Department of Neurobiology, Duke University Medical Center, Durham, North Carolina, USA
| | - Jianmin Cui
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri, USA
| | - Mohamad A Mikati
- Department of Pediatrics, Duke University Medical Center, Durham, North Carolina, USA.,Department of Neurobiology, Duke University Medical Center, Durham, North Carolina, USA
| |
Collapse
|
19
|
Teixeira-Duarte CM, Fonseca F, Morais-Cabral JH. Activation of a nucleotide-dependent RCK domain requires binding of a cation cofactor to a conserved site. eLife 2019; 8:50661. [PMID: 31868587 PMCID: PMC6957272 DOI: 10.7554/elife.50661] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2019] [Accepted: 12/22/2019] [Indexed: 12/24/2022] Open
Abstract
RCK domains regulate the activity of K+ channels and transporters in eukaryotic and prokaryotic organisms by responding to ions or nucleotides. The mechanisms of RCK activation by Ca2+ in the eukaryotic BK and bacterial MthK K+ channels are well understood. However, the molecular details of activation in nucleotide-dependent RCK domains are not clear. Through a functional and structural analysis of the mechanism of ATP activation in KtrA, a RCK domain from the B. subtilis KtrAB cation channel, we have found that activation by nucleotide requires binding of cations to an intra-dimer interface site in the RCK dimer. In particular, divalent cations are coordinated by the γ-phosphates of bound-ATP, tethering the two subunits and stabilizing the active state conformation. Strikingly, the binding site residues are highly conserved in many different nucleotide-dependent RCK domains, indicating that divalent cations are a general cofactor in the regulatory mechanism of many nucleotide-dependent RCK domains.
Collapse
Affiliation(s)
- Celso M Teixeira-Duarte
- Instituto de Investigação e Inovação em Saúde (i3S), Universidade do Porto, Porto, Portugal.,Instituto de Biologia Molecular e Celular (IBMC), Universidade do Porto, Porto, Portugal.,Programa Doutoral em Biologia Molecular e Celular (MCbiology), Instituto de Ciências Biomédicas Abel Salazar (ICBAS), Universidade do Porto, Porto, Portugal
| | - Fátima Fonseca
- Instituto de Investigação e Inovação em Saúde (i3S), Universidade do Porto, Porto, Portugal.,Instituto de Biologia Molecular e Celular (IBMC), Universidade do Porto, Porto, Portugal
| | - João H Morais-Cabral
- Instituto de Investigação e Inovação em Saúde (i3S), Universidade do Porto, Porto, Portugal.,Instituto de Biologia Molecular e Celular (IBMC), Universidade do Porto, Porto, Portugal
| |
Collapse
|
20
|
From Local to Global Modeling for Characterizing Calcium Dynamics and Their Effects on Electrical Activity and Exocytosis in Excitable Cells. Int J Mol Sci 2019; 20:ijms20236057. [PMID: 31801305 PMCID: PMC6928823 DOI: 10.3390/ijms20236057] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2019] [Revised: 11/27/2019] [Accepted: 11/27/2019] [Indexed: 12/25/2022] Open
Abstract
Electrical activity in neurons and other excitable cells is a result of complex interactions between the system of ion channels, involving both global coupling (e.g., via voltage or bulk cytosolic Ca2+ concentration) of the channels, and local coupling in ion channel complexes (e.g., via local Ca2+ concentration surrounding Ca2+ channels (CaVs), the so-called Ca2+ nanodomains). We recently devised a model of large-conductance BKCa potassium currents, and hence BKCa–CaV complexes controlled locally by CaVs via Ca2+ nanodomains. We showed how different CaV types and BKCa–CaV stoichiometries affect whole-cell electrical behavior. Ca2+ nanodomains are also important for triggering exocytosis of hormone-containing granules, and in this regard, we implemented a strategy to characterize the local interactions between granules and CaVs. In this study, we coupled electrical and exocytosis models respecting the local effects via Ca2+ nanodomains. By simulating scenarios with BKCa–CaV complexes with different stoichiometries in pituitary cells, we achieved two main electrophysiological responses (continuous spiking or bursting) and investigated their effects on the downstream exocytosis process. By varying the number and distance of CaVs coupled with the granules, we found that bursting promotes exocytosis with faster rates than spiking. However, by normalizing to Ca2+ influx, we found that bursting is only slightly more efficient than spiking when CaVs are far away from granules, whereas no difference in efficiency between bursting and spiking is observed with close granule-CaV coupling.
Collapse
|
21
|
Lorenzo-Ceballos Y, Carrasquel-Ursulaez W, Castillo K, Alvarez O, Latorre R. Calcium-driven regulation of voltage-sensing domains in BK channels. eLife 2019; 8:44934. [PMID: 31509109 PMCID: PMC6763263 DOI: 10.7554/elife.44934] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2019] [Accepted: 09/10/2019] [Indexed: 12/17/2022] Open
Abstract
Allosteric interactions between the voltage-sensing domain (VSD), the Ca2+-binding sites, and the pore domain govern the mammalian Ca2+- and voltage-activated K+ (BK) channel opening. However, the functional relevance of the crosstalk between the Ca2+- and voltage-sensing mechanisms on BK channel gating is still debated. We examined the energetic interaction between Ca2+ binding and VSD activation by investigating the effects of internal Ca2+ on BK channel gating currents. Our results indicate that Ca2+ sensor occupancy has a strong impact on VSD activation through a coordinated interaction mechanism in which Ca2+ binding to a single α-subunit affects all VSDs equally. Moreover, the two distinct high-affinity Ca2+-binding sites contained in the C-terminus domains, RCK1 and RCK2, contribute equally to decrease the free energy necessary to activate the VSD. We conclude that voltage-dependent gating and pore opening in BK channels is modulated to a great extent by the interaction between Ca2+ sensors and VSDs.
Collapse
Affiliation(s)
- Yenisleidy Lorenzo-Ceballos
- Doctorado en Ciencias Mención Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile.,Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile
| | - Willy Carrasquel-Ursulaez
- 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
| | - Osvaldo Alvarez
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile.,Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago, Chile
| | - Ramon Latorre
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile
| |
Collapse
|
22
|
Gupta S, Manchanda R. A computational model of large conductance voltage and calcium activated potassium channels: implications for calcium dynamics and electrophysiology in detrusor smooth muscle cells. J Comput Neurosci 2019; 46:233-256. [PMID: 31025235 DOI: 10.1007/s10827-019-00713-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2018] [Revised: 02/14/2019] [Accepted: 02/19/2019] [Indexed: 11/25/2022]
Abstract
The large conductance voltage and calcium activated potassium (BK) channels play a crucial role in regulating the excitability of detrusor smooth muscle, which lines the wall of the urinary bladder. These channels have been widely characterized in terms of their molecular structure, pharmacology and electrophysiology. They control the repolarising and hyperpolarising phases of the action potential, thereby regulating the firing frequency and contraction profiles of the smooth muscle. Several groups have reported varied profiles of BK currents and I-V curves under similar experimental conditions. However, no single computational model has been able to reconcile these apparent discrepancies. In view of the channels' physiological importance, it is imperative to understand their mechanistic underpinnings so that a realistic model can be created. This paper presents a computational model of the BK channel, based on the Hodgkin-Huxley formalism, constructed by utilising three activation processes - membrane potential, calcium inflow from voltage-gated calcium channels on the membrane and calcium released from the ryanodine receptors present on the sarcoplasmic reticulum. In our model, we attribute the discrepant profiles to the underlying cytosolic calcium received by the channel during its activation. The model enables us to make heuristic predictions regarding the nature of the sub-membrane calcium dynamics underlying the BK channel's activation. We have employed the model to reproduce various physiological characteristics of the channel and found the simulated responses to be in accordance with the experimental findings. Additionally, we have used the model to investigate the role of this channel in electrophysiological signals, such as the action potential and spontaneous transient hyperpolarisations. Furthermore, the clinical effects of BK channel openers, mallotoxin and NS19504, were simulated for the detrusor smooth muscle cells. Our findings support the proposed application of these drugs for amelioration of the condition of overactive bladder. We thus propose a physiologically realistic BK channel model which can be integrated with other biophysical mechanisms such as ion channels, pumps and exchangers to further elucidate its micro-domain interaction with the intracellular calcium environment.
Collapse
Affiliation(s)
- Suranjana Gupta
- Computational NeuroPhysiology Lab, Department of Biosciences and Bioengineering, IIT Bombay, Powai, Mumbai, 400076, India
| | - Rohit Manchanda
- Computational NeuroPhysiology Lab, Department of Biosciences and Bioengineering, IIT Bombay, Powai, Mumbai, 400076, India.
| |
Collapse
|
23
|
Mahapatra C, Brain KL, Manchanda R. A biophysically constrained computational model of the action potential of mouse urinary bladder smooth muscle. PLoS One 2018; 13:e0200712. [PMID: 30048468 PMCID: PMC6061979 DOI: 10.1371/journal.pone.0200712] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2017] [Accepted: 07/02/2018] [Indexed: 11/19/2022] Open
Abstract
Urinary incontinence is associated with enhanced spontaneous phasic contractions of the detrusor smooth muscle (DSM). Although a complete understanding of the etiology of these spontaneous contractions is not yet established, it is suggested that the spontaneously evoked action potentials (sAPs) in DSM cells initiate and modulate the contractions. In order to further our understanding of the ionic mechanisms underlying sAP generation, we present here a biophysically detailed computational model of a single DSM cell. First, we constructed mathematical models for nine ion channels found in DSM cells based on published experimental data: two voltage gated Ca2+ ion channels, an hyperpolarization-activated ion channel, two voltage-gated K+ ion channels, three Ca2+-activated K+ ion channels and a non-specific background leak ion channel. The ion channels' kinetics were characterized in terms of maximal conductances and differential equations based on voltage or calcium-dependent activation and inactivation. All ion channel models were validated by comparing the simulated currents and current-voltage relations with those reported in experimental work. Incorporating these channels, our DSM model is capable of reproducing experimentally recorded spike-type sAPs of varying configurations, ranging from sAPs displaying after-hyperpolarizations to sAPs displaying after-depolarizations. The contributions of the principal ion channels to spike generation and configuration were also investigated as a means of mimicking the effects of selected pharmacological agents on DSM cell excitability. Additionally, the features of propagation of an AP along a length of electrically continuous smooth muscle tissue were investigated. To date, a biophysically detailed computational model does not exist for DSM cells. Our model, constrained heavily by physiological data, provides a powerful tool to investigate the ionic mechanisms underlying the genesis of DSM electrical activity, which can further shed light on certain aspects of urinary bladder function and dysfunction.
Collapse
Affiliation(s)
- Chitaranjan Mahapatra
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai, Maharashtra, India
| | - Keith L. Brain
- School of Clinical and Experimental Medicine, University of Birmingham, Birmingham, England, United Kingdom
| | - Rohit Manchanda
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai, Maharashtra, India
| |
Collapse
|
24
|
Zhu Y, Ye P, Chen SL, Zhang DM. Functional regulation of large conductance Ca 2+-activated K + channels in vascular diseases. Metabolism 2018; 83:75-80. [PMID: 29373813 DOI: 10.1016/j.metabol.2018.01.008] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/23/2017] [Revised: 01/03/2018] [Accepted: 01/18/2018] [Indexed: 12/17/2022]
Abstract
The large conductance Ca2+-activated potassium channels, the BK channels, is widely expressed in various tissues and activated in a Ca2+- and voltage-dependent manner. The activation of BK channels hyperpolarizes vascular smooth muscle cell membrane potential, resulting in vasodilation. Under pathophysiological conditions, such as diabetes mellitus and hypertension, impaired BK channel function exacerbates vascular vasodilation and leads to organ ischemia. The vascular BK channel is composed of 4 pore-forming subunits, BK-α together with 4 auxiliary subunits: β1 subunits (BK-β1) or γ1 subunits (BK-γ1). Recent studies have shown that down-regulation of the BK β1 subunit in diabetes mellitus induced vascular dysfunction; however, the molecular mechanism of these vascular diseases is not well understood. In this review, we summarize the potential mechanisms regarding BK channelopathy and the potential therapeutic targets of BK channels for vascular diseases.
Collapse
Affiliation(s)
- Yanrong Zhu
- Department of Cardiology, Nanjing First Hospital, Nanjing Medical University, Nanjing, Jiangsu 210006, China
| | - Peng Ye
- Department of Cardiology, Nanjing First Hospital, Nanjing Medical University, Nanjing, Jiangsu 210006, China
| | - Shao-Liang Chen
- Department of Cardiology, Nanjing First Hospital, Nanjing Medical University, Nanjing, Jiangsu 210006, China
| | - Dai-Min Zhang
- Department of Cardiology, Nanjing First Hospital, Nanjing Medical University, Nanjing, Jiangsu 210006, China.
| |
Collapse
|
25
|
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.
Collapse
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.
| |
Collapse
|
26
|
Pinto BI, Pupo A, García IE, Mena-Ulecia K, Martínez AD, Latorre R, Gonzalez C. Calcium binding and voltage gating in Cx46 hemichannels. Sci Rep 2017; 7:15851. [PMID: 29158540 PMCID: PMC5696461 DOI: 10.1038/s41598-017-15975-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2016] [Accepted: 10/24/2017] [Indexed: 12/26/2022] Open
Abstract
The opening of connexin (Cx) hemichannels in the membrane is tightly regulated by calcium (Ca2+) and membrane voltage. Electrophysiological and atomic force microscopy experiments indicate that Ca2+ stabilizes the hemichannel closed state. However, structural data show that Ca2+ binding induces an electrostatic seal preventing ion transport without significant structural rearrangements. In agreement with the closed-state stabilization hypothesis, we found that the apparent Ca2+ sensitivity is increased as the voltage is made more negative. Moreover, the voltage and Ca2+ dependence of the channel kinetics indicate that the voltage sensor movement and Ca2+ binding are allosterically coupled. An allosteric kinetic model in which the Ca2+ decreases the energy necessary to deactivate the voltage sensor reproduces the effects of Ca2+ and voltage in Cx46 hemichannels. In agreement with the model and suggesting a conformational change that narrows the pore, Ca2+ inhibits the water flux through Cx hemichannels. We conclude that Ca2+ and voltage act allosterically to stabilize the closed conformation of Cx46 hemichannels.
Collapse
Affiliation(s)
- Bernardo I Pinto
- Centro Interdisciplinario de Neurociencias de Valparaíso, Universidad de Valparaíso, Valparaíso, Chile
| | - Amaury Pupo
- Centro Interdisciplinario de Neurociencias de Valparaíso, Universidad de Valparaíso, Valparaíso, Chile
| | - Isaac E García
- Centro Interdisciplinario de Neurociencias de Valparaíso, Universidad de Valparaíso, Valparaíso, Chile
- Facultad de Odontología, Universidad de Valparaíso, Valparaíso, Chile
| | - Karel Mena-Ulecia
- Centro Interdisciplinario de Neurociencias de Valparaíso, Universidad de Valparaíso, Valparaíso, Chile
| | - Agustín D Martínez
- Centro Interdisciplinario de Neurociencias de Valparaíso, Universidad de Valparaíso, Valparaíso, Chile
| | - Ramón Latorre
- Centro Interdisciplinario de Neurociencias de Valparaíso, Universidad de Valparaíso, Valparaíso, Chile.
| | - Carlos Gonzalez
- Centro Interdisciplinario de Neurociencias de Valparaíso, Universidad de Valparaíso, Valparaíso, Chile.
| |
Collapse
|
27
|
Zhou Y, Yang H, Cui J, Lingle CJ. Threading the biophysics of mammalian Slo1 channels onto structures of an invertebrate Slo1 channel. J Gen Physiol 2017; 149:985-1007. [PMID: 29025867 PMCID: PMC5677106 DOI: 10.1085/jgp.201711845] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2017] [Accepted: 09/20/2017] [Indexed: 11/24/2022] Open
Abstract
Zhou et al. consider the biophysics of large-conductance Ca2+-activated Slo1 channels in the context of Aplysia Slo1 structures. For those interested in the machinery of ion channel gating, the Ca2+ and voltage-activated BK K+ channel provides a compelling topic for investigation, by virtue of its dual allosteric regulation by both voltage and intracellular Ca2+ and because its large-single channel conductance facilitates detailed kinetic analysis. Over the years, biophysical analyses have illuminated details of the allosteric regulation of BK channels and revealed insights into the mechanism of BK gating, e.g., inner cavity size and accessibility and voltage sensor-pore coupling. Now the publication of two structures of an Aplysia californica BK channel—one liganded and one metal free—promises to reinvigorate functional studies and interpretation of biophysical results. The new structures confirm some of the previous functional inferences but also suggest new perspectives regarding cooperativity between Ca2+-binding sites and the relationship between voltage- and Ca2+-dependent gating. Here we consider the extent to which the two structures explain previous functional data on pore-domain properties, voltage-sensor motions, and divalent cation binding and activation of the channel.
Collapse
Affiliation(s)
- Yu Zhou
- Department of Anesthesiology, Washington University School of Medicine, St. Louis MO
| | - Huanghe Yang
- Department of Biochemistry, Duke University School of Medicine, Durham, NC
| | - Jianmin Cui
- Department of Biomedical Engineering, Washington University, St. Louis, MO
| | - Christopher J Lingle
- Department of Anesthesiology, Washington University School of Medicine, St. Louis MO
| |
Collapse
|
28
|
Burke RC, Bardet SM, Carr L, Romanenko S, Arnaud-Cormos D, Leveque P, O'Connor RP. Nanosecond pulsed electric fields depolarize transmembrane potential via voltage-gated K+, Ca2+ and TRPM8 channels in U87 glioblastoma cells. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2017; 1859:2040-2050. [DOI: 10.1016/j.bbamem.2017.07.004] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/23/2017] [Revised: 07/05/2017] [Accepted: 07/05/2017] [Indexed: 12/20/2022]
|
29
|
Functional validation of Ca 2+-binding residues from the crystal structure of the BK ion channel. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2017; 1860:943-952. [PMID: 28966112 DOI: 10.1016/j.bbamem.2017.09.023] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/26/2017] [Revised: 09/21/2017] [Accepted: 09/24/2017] [Indexed: 12/31/2022]
Abstract
BK channels are dually regulated by voltage and Ca2+, providing a cellular mechanism to couple electrical and chemical signalling. Intracellular Ca2+ concentration is sensed by a large cytoplasmic region in the channel known as "gating ring", which is formed by four tandems of regulator of conductance for K+ (RCK1 and RCK2) domains. The recent crystal structure of the full-length BK channel from Aplysia californica has provided new information about the residues involved in Ca2+ coordination at the high-affinity binding sites located in the RCK1 and RCK2 domains, as well as their cooperativity. Some of these residues have not been previously studied in the human BK channel. In this work we have investigated, through site directed mutagenesis and electrophysiology, the effects of these residues on channel activation by voltage and Ca2+. Our results demonstrate that the side chains of two non-conserved residues proposed to coordinate Ca2+ in the A. californica structure (G523 and E591) have no apparent functional role in the human BK Ca2+ sensing mechanism. Consistent with the crystal structure, our data indicate that in the human channel the conserved residue R514 participates in Ca2+ coordination in the RCK1 binding site. Additionally, this study provides functional evidence indicating that R514 also interacts with residues E902 and Y904 connected to the Ca2+ binding site in RCK2. Interestingly, it has been proposed that this interaction may constitute a structural correlate underlying the cooperative interactions between the two high-affinity Ca2+ binding sites regulating the Ca2+ dependent gating of the BK channel. This article is part of a Special Issue entitled: Beyond the Structure-Function Horizon of Membrane Proteins edited by Ute Hellmich, Rupak Doshi and Benjamin McIlwain.
Collapse
|
30
|
Concise Whole-Cell Modeling of BK Ca-CaV Activity Controlled by Local Coupling and Stoichiometry. Biophys J 2017; 112:2387-2396. [PMID: 28591611 DOI: 10.1016/j.bpj.2017.04.035] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2017] [Revised: 04/12/2017] [Accepted: 04/25/2017] [Indexed: 11/23/2022] Open
Abstract
Large-conductance Ca2+-dependent K+ (BKCa) channels are important regulators of electrical activity. These channels colocalize and form ion channel complexes with voltage-dependent Ca2+ (CaV) channels. Recent stochastic simulations of the BKCa-CaV complex with 1:1 stoichiometry have given important insight into the local control of BKCa channels by fluctuating nanodomains of Ca2+. However, such Monte Carlo simulations are computationally expensive, and are therefore not suitable for large-scale simulations of cellular electrical activity. In this work we extend the stochastic model to more realistic BKCa-CaV complexes with 1:n stoichiometry, and analyze the single-complex model with Markov chain theory. From the description of a single BKCa-CaV complex, using arguments based on timescale analysis, we derive a concise model of whole-cell BKCa currents, which can readily be analyzed and inserted into models of cellular electrical activity. We illustrate the usefulness of our results by inserting our BKCa description into previously published whole-cell models, and perform simulations of electrical activity in various cell types, which show that BKCa-CaV stoichiometry can affect whole-cell behavior substantially. Our work provides a simple formulation for the whole-cell BKCa current that respects local interactions in BKCa-CaV complexes, and indicates how local-global coupling of ion channels may affect cell behavior.
Collapse
|
31
|
Giraldez T, Rothberg BS. Understanding the conformational motions of RCK gating rings. J Gen Physiol 2017; 149:431-441. [PMID: 28246116 PMCID: PMC5379921 DOI: 10.1085/jgp.201611726] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2016] [Accepted: 01/17/2017] [Indexed: 12/16/2022] Open
Abstract
A timely review of the structural basis of Ca2+-activated K+ channel modulation by regulator of conduction of K+ (RCK) domains Regulator of conduction of K+ (RCK) domains are ubiquitous regulators of channel and transporter activity in prokaryotes and eukaryotes. In humans, RCK domains form an integral component of large-conductance calcium-activated K channels (BK channels), key modulators of nerve, muscle, and endocrine cell function. In this review, we explore how the study of RCK domains in bacterial and human channels has contributed to our understanding of the structural basis of channel function. This knowledge will be critical in identifying mechanisms that underlie BK channelopathies that lead to epilepsy and other diseases, as well as regions of the channel that might be successfully targeted to treat such diseases.
Collapse
Affiliation(s)
- Teresa Giraldez
- Department of Basic Medical Sciences, Institute of Biomedical Technologies and Centre for Biomedical Research of the Canary Islands, Universidad de La Laguna, La Laguna 38071, Spain
| | - Brad S Rothberg
- Department of Medical Genetics and Molecular Biochemistry, Temple University Lewis Katz School of Medicine, Philadelphia, PA 19140
| |
Collapse
|
32
|
Zhang G, Geng Y, Jin Y, Shi J, McFarland K, Magleby KL, Salkoff L, Cui J. Deletion of cytosolic gating ring decreases gate and voltage sensor coupling in BK channels. J Gen Physiol 2017; 149:373-387. [PMID: 28196879 PMCID: PMC5339509 DOI: 10.1085/jgp.201611646] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2016] [Revised: 10/28/2016] [Accepted: 12/28/2016] [Indexed: 12/26/2022] Open
Abstract
Both cellular depolarization and intracellular Ca2+ can gate open large conductance Ca2+-activated K+ channels. Zhang et al. show that the intracellular gating ring, which forms the Ca2+-sensing machinery of the channel, is also required for activated voltage sensors to effectively gate open the pore. Large conductance Ca2+-activated K+ channels (BK channels) gate open in response to both membrane voltage and intracellular Ca2+. The channel is formed by a central pore-gate domain (PGD), which spans the membrane, plus transmembrane voltage sensors and a cytoplasmic gating ring that acts as a Ca2+ sensor. How these voltage and Ca2+ sensors influence the common activation gate, and interact with each other, is unclear. A previous study showed that a BK channel core lacking the entire cytoplasmic gating ring (Core-MT) was devoid of Ca2+ activation but retained voltage sensitivity (Budelli et al. 2013. Proc. Natl. Acad. Sci. USA. http://dx.doi.org/10.1073/pnas.1313433110). In this study, we measure voltage sensor activation and pore opening in this Core-MT channel over a wide range of voltages. We record gating currents and find that voltage sensor activation in this truncated channel is similar to WT but that the coupling between voltage sensor activation and gating of the pore is reduced. These results suggest that the gating ring, in addition to being the Ca2+ sensor, enhances the effective coupling between voltage sensors and the PGD. We also find that removal of the gating ring alters modulation of the channels by the BK channel’s β1 and β2 subunits.
Collapse
Affiliation(s)
- Guohui Zhang
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University, St. Louis, MO 63130
| | - Yanyan Geng
- Department of Physiology and Biophysics, University of Miami Miller School of Medicine, Miami, FL 33136
| | - Yakang Jin
- Department of Pharmacology, Soochow University College of Pharmaceutical Sciences, Suzhou 215123, China
| | - Jingyi Shi
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University, St. Louis, MO 63130
| | - Kelli McFarland
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University, St. Louis, MO 63130
| | - Karl L Magleby
- Department of Physiology and Biophysics, University of Miami Miller School of Medicine, Miami, FL 33136
| | - Lawrence Salkoff
- Department of Anatomy and Neurobiology (Department of Neuroscience), Washington University School of Medicine in St. Louis, St. Louis, MO 63110.,Department of Genetics, Washington University School of Medicine in St. Louis, St. Louis, MO 63110
| | - Jianmin Cui
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University, St. Louis, MO 63130 .,Department of Pharmacology, Soochow University College of Pharmaceutical Sciences, Suzhou 215123, China
| |
Collapse
|
33
|
Mager T, Wood PG, Bamberg E. Optogenetic Control of Ca 2+ and Voltage-Dependent Large Conductance (BK) Potassium Channels. J Mol Biol 2017; 429:911-921. [PMID: 28192090 DOI: 10.1016/j.jmb.2017.02.004] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2016] [Revised: 01/31/2017] [Accepted: 02/06/2017] [Indexed: 12/23/2022]
Abstract
Ca2+ concentration jumps for the activation of Ca2+-dependent ion channels or transporters can be obtained either by fast solution exchange or by the use of caged Ca2+. Here, we report on an alternate optogenetic method for the activation of Ca2+ and voltage-dependent large conductance (BK) potassium channels. This was achieved through the use of the light-gated channelrhodopsin 2 variant, CatCh(Calcium translocating Channelrhodopsin) with enhanced Ca, which produces locally [Ca2+] in the μM range on the inner side of the membrane, without significant [Ca2+] increase in the cytosol. BK channel subunits α and β1 were expressed together with CatCh in HEK293 cells, and voltage and Ca2+ dependence were analyzed. Light activation of endogenous BK channels under native conditions in astrocytes and glioma cells was also investigated. Additionally, BK channels were used as sensors for the calibration of the [Ca2+] on the inner surface of the cell membrane.
Collapse
Affiliation(s)
- Thomas Mager
- Max Planck Institute of Biophysics, Department of Biophysical Chemistry, 60438 Frankfurt am Main, Germany.
| | - Phillip G Wood
- Max Planck Institute of Biophysics, Department of Biophysical Chemistry, 60438 Frankfurt am Main, Germany.
| | - Ernst Bamberg
- Max Planck Institute of Biophysics, Department of Biophysical Chemistry, 60438 Frankfurt am Main, Germany.
| |
Collapse
|
34
|
A quantized mechanism for activation of pannexin channels. Nat Commun 2017; 8:14324. [PMID: 28134257 PMCID: PMC5290276 DOI: 10.1038/ncomms14324] [Citation(s) in RCA: 106] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2016] [Accepted: 12/16/2016] [Indexed: 11/18/2022] Open
Abstract
Pannexin 1 (PANX1) subunits form oligomeric plasma membrane channels that mediate nucleotide release for purinergic signalling, which is involved in diverse physiological processes such as apoptosis, inflammation, blood pressure regulation, and cancer progression and metastasis. Here we explore the mechanistic basis for PANX1 activation by using wild type and engineered concatemeric channels. We find that PANX1 activation involves sequential stepwise sojourns through multiple discrete open states, each with unique channel gating and conductance properties that reflect contributions of the individual subunits of the hexamer. Progressive PANX1 channel opening is directly linked to permeation of ions and large molecules (ATP and fluorescent dyes) and occurs during both irreversible (caspase cleavage-mediated) and reversible (α1 adrenoceptor-mediated) forms of channel activation. This unique, quantized activation process enables fine tuning of PANX1 channel activity and may be a generalized regulatory mechanism for other related multimeric channels. Pannexins are oligomeric plasma membrane channels that allow permeation of ions and large molecules. Here the authors show that human Pannexin 1 activation is a multistep event, where modification of each monomer opens the channel to a unique conductance state and fine tunes its activity.
Collapse
|
35
|
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
|
36
|
Interactions of divalent cations with calcium binding sites of BK channels reveal independent motions within the gating ring. Proc Natl Acad Sci U S A 2016; 113:14055-14060. [PMID: 27872281 DOI: 10.1073/pnas.1611415113] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Large-conductance voltage- and calcium-activated K+ (BK) channels are key physiological players in muscle, nerve, and endocrine function by integrating intracellular Ca2+ and membrane voltage signals. The open probability of BK channels is regulated by the intracellular concentration of divalent cations sensed by a large structure in the BK channel called the "gating ring," which is formed by four tandems of regulator of conductance for K+ (RCK1 and RCK2) domains. In contrast to Ca2+ that binds to both RCK domains, Mg2+, Cd2+, or Ba2+ interact preferentially with either one or the other. Interaction of cations with their binding sites causes molecular rearrangements of the gating ring, but how these motions occur remains elusive. We have assessed the separate contributions of each RCK domain to the cation-induced gating-ring structural rearrangements, using patch-clamp fluorometry. Here we show that Mg2+ and Ba2+ selectively induce structural movement of the RCK2 domain, whereas Cd2+ causes motions of RCK1, in all cases substantially smaller than those elicited by Ca2+ By combining divalent species interacting with unique sites, we demonstrate that RCK1 and RCK2 domains move independently when their specific binding sites are occupied. Moreover, binding of chemically distinct cations to both RCK domains is additive, emulating the effect of fully occupied Ca2+ binding sites.
Collapse
|
37
|
Wang B, Bugay V, Ling L, Chuang HH, Jaffe DB, Brenner R. Knockout of the BK β4-subunit promotes a functional coupling of BK channels and ryanodine receptors that mediate a fAHP-induced increase in excitability. J Neurophysiol 2016; 116:456-65. [PMID: 27146987 PMCID: PMC4978790 DOI: 10.1152/jn.00857.2015] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2015] [Accepted: 05/03/2016] [Indexed: 01/24/2023] Open
Abstract
BK channels are large-conductance calcium- and voltage-activated potassium channels with diverse properties. Knockout of the accessory BK β4-subunit in hippocampus dentate gyrus granule neurons causes BK channels to change properties from slow-gated type II channels to fast-gated type I channels that sharpen the action potential, increase the fast afterhyperpolarization (fAHP) amplitude, and increase spike frequency. Here we studied the calcium channels that contribute to fast-gated BK channel activation and increased excitability of β4 knockout neurons. By using pharmacological blockers during current-clamp recording, we find that BK channel activation during the fAHP is dependent on ryanodine receptor activation. In contrast, L-type calcium channel blocker (nifedipine) affects the BK channel-dependent repolarization phase of the action potential but has no effect on the fAHP. Reducing BK channel activation during the repolarization phase with nifedipine, or during the fAHP with ryanodine, indicated that it is the BK-mediated increase of the fAHP that confers proexcitatory effects. The proexcitatory role of the fAHP was corroborated using dynamic current clamp. Increase or decrease of the fAHP amplitude during spiking revealed an inverse relationship between fAHP amplitude and interspike interval. Finally, we show that the seizure-prone ryanodine receptor gain-of-function (R2474S) knockin mice have an unaltered repolarization phase but larger fAHP and increased AP frequency compared with their control littermates. In summary, these results indicate that an important role of the β4-subunit is to reduce ryanodine receptor-BK channel functional coupling during the fAHP component of the action potential, thereby decreasing excitability of dentate gyrus neurons.
Collapse
Affiliation(s)
- Bin Wang
- Department of Physiology, The University of Texas Health Science Center at San Antonio, San Antonio, Texas; and
| | - Vladislav Bugay
- Department of Physiology, The University of Texas Health Science Center at San Antonio, San Antonio, Texas; and
| | - Ling Ling
- Department of Physiology, The University of Texas Health Science Center at San Antonio, San Antonio, Texas; and
| | - Hui-Hsui Chuang
- Department of Physiology, The University of Texas Health Science Center at San Antonio, San Antonio, Texas; and
| | - David B Jaffe
- Department of Biology, University of Texas at San Antonio, San Antonio, Texas
| | - Robert Brenner
- Department of Physiology, The University of Texas Health Science Center at San Antonio, San Antonio, Texas; and
| |
Collapse
|
38
|
Janssens A, Gees M, Toth BI, Ghosh D, Mulier M, Vennekens R, Vriens J, Talavera K, Voets T. Definition of two agonist types at the mammalian cold-activated channel TRPM8. eLife 2016; 5. [PMID: 27449282 PMCID: PMC4985286 DOI: 10.7554/elife.17240] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2016] [Accepted: 07/22/2016] [Indexed: 11/13/2022] Open
Abstract
Various TRP channels act as polymodal sensors of thermal and chemical stimuli, but the mechanisms whereby chemical ligands impact on TRP channel gating are poorly understood. Here we show that AITC (allyl isothiocyanate; mustard oil) and menthol represent two distinct types of ligands at the mammalian cold sensor TRPM8. Kinetic analysis of channel gating revealed that AITC acts by destabilizing the closed channel, whereas menthol stabilizes the open channel, relative to the transition state. Based on these differences, we classify agonists as either type I (menthol-like) or type II (AITC-like), and provide a kinetic model that faithfully reproduces their differential effects. We further demonstrate that type I and type II agonists have a distinct impact on TRPM8 currents and TRPM8-mediated calcium signals in excitable cells. These findings provide a theoretical framework for understanding the differential actions of TRP channel ligands, with important ramifications for TRP channel structure-function analysis and pharmacology. DOI:http://dx.doi.org/10.7554/eLife.17240.001 Sensory neurons in our skin detect cues from the environment – such as temperature and touch – and pass the information onto other cells in the nervous system. A protein called TRPM8 in sensory neurons is responsible for our ability to detect cool temperatures. TRPM8 sits in the membrane that surrounds the cell and forms a channel that can allow sodium and calcium ions to enter the cell. Cold temperatures activate TRPM8, which opens the channel and triggers electrical activity in the sensory neurons. Chemicals that cause a cold sensation – such as menthol, the refreshing substance found in mint plants – can also open the TRPM8 channel. Janssens, Gees, Toth et al. investigated how menthol, and another natural compound called mustard oil, influence the opening of TRPM8. The experiments show that menthol and mustard oil both stimulate sensory neurons by opening the TRPM8 ion channel, but using different mechanisms. Mustard oil forces the channel to open faster than it normally would, whereas menthol prevents the channel from closing. Further experiments show that these mechanisms explain why some compounds stimulate sensory neurons more strongly than others. The findings of Janssens, Gees, Toth et al. will help to understand how chemicals act on this class of ion channels, and how this affects the roles of the ion channels in cells. Altering the activity of TRPM8 and related ion channels may help to reduce pain in humans so a future challenge is to use these new insights to develop drugs that target these channels more efficiently. DOI:http://dx.doi.org/10.7554/eLife.17240.002
Collapse
Affiliation(s)
- Annelies Janssens
- Laboratory of Ion Channel Research and TRP channel Research Platform Leuven, Department of Cellular and Molecular Medicine, University of Leuven, Leuven, Belgium
| | - Maarten Gees
- Laboratory of Ion Channel Research and TRP channel Research Platform Leuven, Department of Cellular and Molecular Medicine, University of Leuven, Leuven, Belgium
| | - Balazs Istvan Toth
- Laboratory of Ion Channel Research and TRP channel Research Platform Leuven, Department of Cellular and Molecular Medicine, University of Leuven, Leuven, Belgium
| | - Debapriya Ghosh
- Laboratory of Ion Channel Research and TRP channel Research Platform Leuven, Department of Cellular and Molecular Medicine, University of Leuven, Leuven, Belgium
| | - Marie Mulier
- Laboratory of Ion Channel Research and TRP channel Research Platform Leuven, Department of Cellular and Molecular Medicine, University of Leuven, Leuven, Belgium
| | - Rudi Vennekens
- Laboratory of Ion Channel Research and TRP channel Research Platform Leuven, Department of Cellular and Molecular Medicine, University of Leuven, Leuven, Belgium
| | - Joris Vriens
- Laboratory of Ion Channel Research and TRP channel Research Platform Leuven, Department of Cellular and Molecular Medicine, University of Leuven, Leuven, Belgium.,Laboratory of Experimental Gynaecology, University of Leuven, Leuven, Belgium
| | - Karel Talavera
- Laboratory of Ion Channel Research and TRP channel Research Platform Leuven, Department of Cellular and Molecular Medicine, University of Leuven, Leuven, Belgium
| | - Thomas Voets
- Laboratory of Ion Channel Research and TRP channel Research Platform Leuven, Department of Cellular and Molecular Medicine, University of Leuven, Leuven, Belgium
| |
Collapse
|
39
|
Cox DH. Modeling a Ca(2+) channel/BKCa channel complex at the single-complex level. Biophys J 2016; 107:2797-2814. [PMID: 25517147 DOI: 10.1016/j.bpj.2014.10.069] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2014] [Revised: 09/26/2014] [Accepted: 10/23/2014] [Indexed: 11/18/2022] Open
Abstract
BKCa-channel activity often affects the firing properties of neurons, the shapes of neuronal action potentials (APs), and in some cases the extent of neurotransmitter release. It has become clear that BKCa channels often form complexes with voltage-gated Ca(2+) channels (CaV channels) such that when a CaV channel is activated, the ensuing influx of Ca(2+) activates its closely associated BKCa channel. Thus, in modeling the electrical properties of neurons, it would be useful to have quantitative models of CaV/BKCa complexes. Furthermore, in a population of CaV/BKCa complexes, all BKCa channels are not exposed to the same Ca(2+) concentration at the same time. Thus, stochastic rather than deterministic models are required. To date, however, no such models have been described. Here, however, I present a stochastic model of a CaV2.1/BKCa(α-only) complex, as might be found in a central nerve terminal. The CaV2.1/BKCa model is based on kinetic modeling of its two component channels at physiological temperature. Surprisingly, The CaV2.1/BKCa model predicts that although the CaV channel will open nearly every time during a typical cortical AP, its associated BKCa channel is expected to open in only 30% of trials, and this percentage is very sensitive to the duration of the AP, the distance between the two channels in the complex, and the presence of fast internal Ca(2+) buffers. Also, the model predicts that the kinetics of the BKCa currents of a population of CaV2.1/BKCa complexes will not be limited by the kinetics of the CaV2.1 channel, and during a train of APs, the current response of the complex is expected to faithfully follow even very rapid trains. Aside from providing insight into how these complexes are likely to behave in vivo, the models presented here could also be of use more generally as components of higher-level models of neural function.
Collapse
Affiliation(s)
- Daniel H Cox
- Department of Neuroscience, Tufts University School of Medicine, Boston, Massachusetts.
| |
Collapse
|
40
|
Hoshi T, Heinemann SH. Modulation of BK Channels by Small Endogenous Molecules and Pharmaceutical Channel Openers. INTERNATIONAL REVIEW OF NEUROBIOLOGY 2016; 128:193-237. [PMID: 27238265 DOI: 10.1016/bs.irn.2016.03.020] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Voltage- and Ca(2+)-activated K(+) channels of big conductance (BK channels) are abundantly found in various organs and their relevance for smooth muscle tone and neuronal signaling is well documented. Dysfunction of BK channels is implicated in an array of human diseases involving many organs including the nervous, pulmonary, cardiovascular, renal, and urinary systems. In humans a single gene (KCNMA1) encodes the pore-forming α subunit (Slo1) of BK channels, but the channel properties are variable because of alternative splicing, tissue- and subcellular-specific auxiliary subunits (β, γ), posttranslational modifications, and a multitude of endogenous signaling molecules directly affecting the channel function. Initiatives to develop drugs capable of activating BK channels (channel openers) therefore need to consider the tissue-specific variability of BK channel structure and the potential interference with endogenously produced regulatory factors. The atomic structural basis of BK channel function is only beginning to be revealed. However, building on detailed knowledge of BK channel function, including its single-channel characteristics, voltage- and Ca(2+) dependence of channel gating, and modulation by diffusible messengers, a multi-tier allosteric model of BK channel gating (Horrigan and Aldrich (HA) model) has become a valuable tool in studying modulation of the channel. Using the conceptual framework of the HA model, we here review the functional impact of endogenous modulatory factors and select small synthetic compounds that regulate BK channel activity. Furthermore, we devise experimental approaches for studying BK channel-drug interactions with the aim to classify BK-modulating substances according to their molecular mode of action.
Collapse
Affiliation(s)
- T Hoshi
- University of Pennsylvania, Philadelphia, PA, United States.
| | - S H Heinemann
- Friedrich Schiller University Jena & Jena University Hospital, Jena, Germany
| |
Collapse
|
41
|
Novel cell-free high-throughput screening method for pharmacological tools targeting K+ channels. Proc Natl Acad Sci U S A 2016; 113:5748-53. [PMID: 27091997 DOI: 10.1073/pnas.1602815113] [Citation(s) in RCA: 70] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
K(+) channels, a superfamily of ∼80 members, control cell excitability, ion homeostasis, and many forms of cell signaling. Their malfunctions cause numerous diseases including neuronal disorders, cardiac arrhythmia, diabetes, and asthma. Here we present a novel liposome flux assay (LFA) that is applicable to most K(+) channels. It is robust, low cost, and high throughput. Using LFA, we performed small molecule screens on three different K(+) channels and identified new activators and inhibitors for biological research on channel function and for medicinal development. We further engineered a hERG (human ether-à-go-go-related gene) channel, which, when used in LFA, provides a highly sensitive (zero false negatives on 50 hERG-sensitive drugs) and highly specific (zero false positives on 50 hERG-insensitive drugs), low-cost hERG safety assay.
Collapse
|
42
|
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
|
43
|
Extrapolating microdomain Ca(2+) dynamics using BK channels as a Ca(2+) sensor. Sci Rep 2016; 6:17343. [PMID: 26776352 PMCID: PMC4726033 DOI: 10.1038/srep17343] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2014] [Accepted: 10/22/2015] [Indexed: 11/17/2022] Open
Abstract
Ca2+ ions play crucial roles in mediating physiological and pathophysiological processes, yet Ca2+ dynamics local to the Ca2+ source, either from influx via calcium permeable ion channels on plasmic membrane or release from internal Ca2+ stores, is difficult to delineate. Large-conductance calcium-activated K+ (BK-type) channels, abundantly distribute in excitable cells and often localize to the proximity of voltage-gated Ca2+ channels (VGCCs), spatially enabling the coupling of the intracellular Ca2+ signal to the channel gating to regulate membrane excitability and spike firing patterns. Here we utilized the sensitivity and dynamic range of BK to explore non-uniform Ca2+ local transients in the microdomain of VGCCs. Accordingly, we applied flash photolysis of caged Ca2+ to activate BK channels and determine their intrinsic sensitivity to Ca2+. We found that uncaging Ca2+ activated biphasic BK currents with fast and slow components (time constants being τf ≈ 0.2 ms and τs ≈ 10 ms), which can be accounted for by biphasic Ca2+ transients following light photolysis. We estimated the Ca2+-binding rate constant kb (≈1.8 × 108 M−1s−1) for mSlo1 and further developed a model in which BK channels act as a calcium sensor capable of quantitatively predicting local microdomain Ca2+ transients in the vicinity of VGCCs during action potentials.
Collapse
|
44
|
Stoler O, Fleidervish IA. Functional implications of axon initial segment cytoskeletal disruption in stroke. Acta Pharmacol Sin 2016; 37:75-81. [PMID: 26687934 DOI: 10.1038/aps.2015.107] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2015] [Accepted: 10/28/2015] [Indexed: 12/19/2022] Open
Abstract
Axon initial segment (AIS) is the proximal part of the axon, which is not covered with a myelin sheath and possesses a distinctive, specialized assembly of voltage-gated ion channels and associated proteins. AIS plays critical roles in synaptic integration and action potential generation in central neurons. Recent evidence shows that stroke causes rapid, irreversible calpain-mediated proteolysis of the AIS cytoskeleton of neurons surrounding the ischemic necrotic core. A better understanding of the molecular mechanisms underlying this "non-lethal" neuronal damage might provide new therapeutic strategies for improving stroke outcome. Here, we present a brief overview of the structure and function of the AIS. We then discuss possible mechanisms underlying stroke-induced AIS damage, including the roles of calpains and possible sources of Ca(2+) ions, which are necessary for the activation of calpains. Finally, we discuss the potential functional implications of the loss of the AIS cytoskeleton and ion channel clusters for neuronal excitability.
Collapse
|
45
|
Hines KE, Bankston JR, Aldrich RW. Analyzing single-molecule time series via nonparametric Bayesian inference. Biophys J 2015; 108:540-56. [PMID: 25650922 DOI: 10.1016/j.bpj.2014.12.016] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2014] [Revised: 12/03/2014] [Accepted: 12/08/2014] [Indexed: 12/22/2022] Open
Abstract
The ability to measure the properties of proteins at the single-molecule level offers an unparalleled glimpse into biological systems at the molecular scale. The interpretation of single-molecule time series has often been rooted in statistical mechanics and the theory of Markov processes. While existing analysis methods have been useful, they are not without significant limitations including problems of model selection and parameter nonidentifiability. To address these challenges, we introduce the use of nonparametric Bayesian inference for the analysis of single-molecule time series. These methods provide a flexible way to extract structure from data instead of assuming models beforehand. We demonstrate these methods with applications to several diverse settings in single-molecule biophysics. This approach provides a well-constrained and rigorously grounded method for determining the number of biophysical states underlying single-molecule data.
Collapse
Affiliation(s)
- Keegan E Hines
- Center for Learning and Memory and Department of Neuroscience, University of Texas at Austin, Austin, Texas
| | - John R Bankston
- Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle, Washington
| | - Richard W Aldrich
- Center for Learning and Memory and Department of Neuroscience, University of Texas at Austin, Austin, Texas.
| |
Collapse
|
46
|
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.
Collapse
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
| |
Collapse
|
47
|
Abstract
The receptor channel TRPV1 (Transient Receptor Potential Vanilloid 1) is expressed by primary afferent sensory neurons of the pain pathway, where it functions as a sensor of noxious heat and various chemicals, including eicosanoids, capsaicin, protons and peptide toxins. Comprised of four identical subunits that organize into a non-selective cationic permeable channel, this receptor has a variety of binding sites responsible for detecting their respective agonists. Although its physiological role as a chemosensor has been described in detail, the stoichiometry of TRPV1 activation by its different ligands remains unknown. Here, we combined the use of concatemeric constructs harboring mutated binding sites with patch-clamp recordings in order to determine the stoichiometry for TRPV1 activation through the vanilloid binding site and the outer-pore domain by capsaicin and protons, respectively. We show that, while a single capsaicin-bound subunit was sufficient to achieve a maximal open-channel lifetime, all four proton-binding sites were required. Thus, our results demonstrate a distinct stoichiometry of TRPV1 activation through two of its different agonist-binding domains.
Collapse
|
48
|
Carrasquel-Ursulaez W, Moldenhauer H, Castillo JP, Latorre R, Alvarez O. Biophysical analysis of thermosensitive TRP channels with a special focus on the cold receptor TRPM8. Temperature (Austin) 2015; 2:188-200. [PMID: 27227023 PMCID: PMC4843903 DOI: 10.1080/23328940.2015.1047558] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2015] [Revised: 04/28/2015] [Accepted: 04/29/2015] [Indexed: 11/03/2022] Open
Abstract
Mammals maintain homeostatic control of their body temperature. Therefore, these organisms are expected to have adaptations that confer the ability to detect and react to both self and ambient temperature. Temperature-activated ion channels have been discovered to be the primary molecular determinants of thermosensation. The most representative group of these determinants constitutes members of the transient receptor potential superfamily, TRP, which are activated by either low or high temperatures covering the whole range of physiologically relevant temperatures. This review makes a critical assessment of existing analytical methods of temperature-activated TRP channel mechanisms using the cold-activated TRPM8 channel as a paradigm.
Collapse
Key Words
- DRG, dorsal root ganglion
- F, Faraday
- G0, Standard molar Gibbs free energy
- H0, Standard molar enthalpy
- Q10, temperature coefficient
- R, universal gas constant
- S0, Standard molar entropy
- T, temperature
- TG, trigeminal ganglion
- TRP, transient receptor potential
Collapse
Affiliation(s)
- Willy Carrasquel-Ursulaez
- Centro Interdisciplinario de Neurociencia de Valparaíso; Universidad de Valparaíso; Valparaíso, Chile; Doctorado en Ciencias Mención Neurociencias; Facultad de Ciencias; Universidad de Valparaíso; Valparaíso, Chile
| | - Hans Moldenhauer
- Centro Interdisciplinario de Neurociencia de Valparaíso; Universidad de Valparaíso ; Valparaíso, Chile
| | - Juan Pablo Castillo
- Centro Interdisciplinario de Neurociencia de Valparaíso; Universidad de Valparaíso ; Valparaíso, Chile
| | - Ramón Latorre
- 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
| |
Collapse
|
49
|
Abstract
Calcium ions are Nature's most widely used signaling mechanism, mediating communication between pathways at virtually every physiological level. Ion channels are no exception, as the activities of a wide range of ion channels are intricately shaped by fluctuations in intracellular Ca(2+) levels. Mirroring the importance and the breadth of Ca(2+) signaling, free Ca(2+) levels are tightly controlled, and a myriad of Ca(2+) binding proteins transduce Ca(2+) signals, each with its own nuance, comprising a constantly changing symphony of metabolic activity. The founding member of Ca(2+) binding proteins is calmodulin (CaM), a small, acidic, modular protein endowed with gymnastic-like flexibility and E-F hand motifs that chelate Ca(2+) ions. In this review, I will trace the history that led to the realization that CaM serves as the Ca(2+)-gating cue for SK channels, the experiments that revealed that CaM is an intrinsic subunit of SK channels, and itself a target of regulation.
Collapse
Affiliation(s)
- John P Adelman
- a Vollum Institute ; Oregon Health & Science University ; Portland , OR USA
| |
Collapse
|
50
|
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: 86] [Impact Index Per Article: 9.6] [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.
Collapse
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
| |
Collapse
|