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Schwenzer N, Teiwes NK, Kohl T, Pohl C, Giller MJ, Lehnart SE, Steinem C. Ca V1.3 channel clusters characterized by live-cell and isolated plasma membrane nanoscopy. Commun Biol 2024; 7:620. [PMID: 38783117 PMCID: PMC11116533 DOI: 10.1038/s42003-024-06313-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2023] [Accepted: 05/08/2024] [Indexed: 05/25/2024] Open
Abstract
A key player of excitable cells in the heart and brain is the L-type calcium channel CaV1.3. In the heart, it is required for voltage-dependent Ca2+-signaling, i.e., for controlling and modulating atrial cardiomyocyte excitation-contraction coupling. The clustering of CaV1.3 in functionally relevant channel multimers has not been addressed due to a lack of stoichiometric labeling combined with high-resolution imaging. Here, we developed a HaloTag-labeling strategy to visualize and quantify CaV1.3 clusters using STED nanoscopy to address the questions of cluster size and intra-cluster channel density. Channel clusters were identified in the plasma membrane of transfected live HEK293 cells as well as in giant plasma membrane vesicles derived from these cells that were spread on modified glass support to obtain supported plasma membrane bilayers (SPMBs). A small fraction of the channel clusters was colocalized with early and recycling endosomes at the membranes. STED nanoscopy in conjunction with live-cell and SPMB imaging enabled us to quantify CaV1.3 cluster sizes and their molecular density revealing significantly lower channel densities than expected for dense channel packing. CaV1.3 channel cluster size and molecular density were increased in SPMBs after treatment of the cells with the sympathomimetic compound isoprenaline, suggesting a regulated channel cluster condensation mechanism.
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Affiliation(s)
- Niko Schwenzer
- Department of Cardiology and Pneumology, University Medical Center Göttingen, Robert-Koch-Str. 40, 37075, Göttingen, Germany
- Cellular Biophysics and Translational Cardiology Section, Heart Research Center Göttingen, University Medical Center Göttingen, Robert‑Koch‑Str. 42a, 37075, Göttingen, Germany
- Cluster of Excellence "Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells" (MBExC 2067), University of Göttingen, 37073, Göttingen, Germany
| | - Nikolas K Teiwes
- Cluster of Excellence "Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells" (MBExC 2067), University of Göttingen, 37073, Göttingen, Germany
- Georg-August Universität, Institut für Organische und Biomolekulare Chemie, Tammannstr. 2, 37077, Göttingen, Germany
| | - Tobias Kohl
- Department of Cardiology and Pneumology, University Medical Center Göttingen, Robert-Koch-Str. 40, 37075, Göttingen, Germany
- Cellular Biophysics and Translational Cardiology Section, Heart Research Center Göttingen, University Medical Center Göttingen, Robert‑Koch‑Str. 42a, 37075, Göttingen, Germany
- DZHK (German Centre for Cardiovascular Research), partner site Göttingen, Robert-Koch-Str. 40, 37075, Göttingen, Germany
| | - Celine Pohl
- Georg-August Universität, Institut für Organische und Biomolekulare Chemie, Tammannstr. 2, 37077, Göttingen, Germany
| | - Michelle J Giller
- Georg-August Universität, Institut für Organische und Biomolekulare Chemie, Tammannstr. 2, 37077, Göttingen, Germany
| | - Stephan E Lehnart
- Department of Cardiology and Pneumology, University Medical Center Göttingen, Robert-Koch-Str. 40, 37075, Göttingen, Germany.
- Cellular Biophysics and Translational Cardiology Section, Heart Research Center Göttingen, University Medical Center Göttingen, Robert‑Koch‑Str. 42a, 37075, Göttingen, Germany.
- Cluster of Excellence "Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells" (MBExC 2067), University of Göttingen, 37073, Göttingen, Germany.
- DZHK (German Centre for Cardiovascular Research), partner site Göttingen, Robert-Koch-Str. 40, 37075, Göttingen, Germany.
- Collaborative Research Center SFB 1190 "Compartmental Gates and Contact Sites in Cells", University of Göttingen, Humboldtallee 23, 37073, Göttingen, Germany.
| | - Claudia Steinem
- Cluster of Excellence "Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells" (MBExC 2067), University of Göttingen, 37073, Göttingen, Germany.
- Georg-August Universität, Institut für Organische und Biomolekulare Chemie, Tammannstr. 2, 37077, Göttingen, Germany.
- Max-Planck-Institut für Dynamik und Selbstorganisation, Am Fassberg 17, 37077, Göttingen, Germany.
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Santos DOC, Trindade MAS, da Silva AJ. Nonextensive realizations in interacting ion channels: Implications for mechano-electrical transducer mechanisms. Biosystems 2023; 232:105005. [PMID: 37611860 DOI: 10.1016/j.biosystems.2023.105005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2023] [Revised: 08/12/2023] [Accepted: 08/19/2023] [Indexed: 08/25/2023]
Abstract
We propose a theoretical model to investigate the thermodynamics of single and coupled two-state ion channels, associated with mechanoelectrical transduction (MET) and hair cell biophysics. The modeling was based on the Tsallis nonextensive statistical mechanics. The choice for a nonextensive framework in modeling ion channels is encouraged on the fact that we take into account the presence of interactions or long-range correlations in the dynamics of single and coupled ion channels. However, the basic assumptions that support Boltzmann-Gibbs statistics, traditionally used to model ion channel dynamics, state that the system is formed by independent or weakly interacting elements. Despite being well studied in many biological systems, the literature has not yet addressed the study of both entropy and mutual information related to isolated or physically interacting pairs of MET channels. Inspired by hair cell biophysics, we show how the presence of nonextensivity, or subadditivity and superadditivity modulates the nonextensive entropy and mutual information as functions of stereocilia displacements. We also observe that the magnitude of the interaction between the two channels, given by a nonextensive parameter, influences the amplitude of the nonextensive joint entropy and mutual information as functions of the hair cell displacements. Finally, we show how nonextensivity regulates the current versus displacement curve for a single and a pair of interacting two-state channels. The present findings shed light on the thermodynamic process involved in the molecular mechanisms of the auditory system.
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Affiliation(s)
- D O C Santos
- Universidade Federal do Sul da Bahia, CEP 45600-923, Itabuna, Bahia, Brazil
| | - M A S Trindade
- Colegiado de Física, Departamento de Ciências Exatas e da Terra, Universidade do Estado da Bahia, CEP 41150-000, Salvador, Bahia, Brazil
| | - A J da Silva
- Universidade Federal do Sul da Bahia, CEP 45600-923, Itabuna, Bahia, Brazil.
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Nsasra E, Dahan I, Eichler J, Yifrach O. It's Time for Entropic Clocks: The Roles of Random Chain Protein Sequences in Timing Ion Channel Processes Underlying Action Potential Properties. ENTROPY (BASEL, SWITZERLAND) 2023; 25:1351. [PMID: 37761650 PMCID: PMC10527868 DOI: 10.3390/e25091351] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/30/2023] [Revised: 09/10/2023] [Accepted: 09/13/2023] [Indexed: 09/29/2023]
Abstract
In recent years, it has become clear that intrinsically disordered protein segments play diverse functional roles in many cellular processes, thus leading to a reassessment of the classical structure-function paradigm. One class of intrinsically disordered protein segments is entropic clocks, corresponding to unstructured random protein chains involved in timing cellular processes. Such clocks were shown to modulate ion channel processes underlying action potential generation, propagation, and transmission. In this review, we survey the role of entropic clocks in timing intra- and inter-molecular binding events of voltage-activated potassium channels involved in gating and clustering processes, respectively, and where both are known to occur according to a similar 'ball and chain' mechanism. We begin by delineating the thermodynamic and timing signatures of a 'ball and chain'-based binding mechanism involving entropic clocks, followed by a detailed analysis of the use of such a mechanism in the prototypical Shaker voltage-activated K+ channel model protein, with particular emphasis on ion channel clustering. We demonstrate how 'chain'-level alternative splicing of the Kv channel gene modulates entropic clock-based 'ball and chain' inactivation and clustering channel functions. As such, the Kv channel model system exemplifies how linkage between alternative splicing and intrinsic disorder enables the functional diversity underlying changes in electrical signaling.
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Affiliation(s)
| | | | | | - Ofer Yifrach
- Department of Life Sciences, School of Brain Sciences and Cognition, Ben-Gurion University of the Negev, P.O. Box 653, Beer Sheva 84105, Israel; (E.N.); (J.E.)
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Ankri N, Debanne D. A fast Markovian method for modeling channel noise in neurons. Heliyon 2023; 9:e16953. [PMID: 37484233 PMCID: PMC10361033 DOI: 10.1016/j.heliyon.2023.e16953] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2022] [Revised: 04/17/2023] [Accepted: 06/01/2023] [Indexed: 07/25/2023] Open
Abstract
Channel noise results from rapid transitions of protein channels from closed to open state and is generally considered as the most dominant source of electrical noise causing membrane-potential fluctuations even in the absence of synaptic inputs. The simulation of a realistic channel noise remains a source of possible error. Although the Markovian method is considered as the golden standard for appropriate description of channel noise, its computation time increasing exponentially with the number of channels, it is poorly suitable to simulate realistic features. We describe here a novel algorithm at discrete time unit for simulating ion channel noise based on Markov chains (MC). Although this new algorithm refers to a Monte-Carlo process, it only needs few random numbers whatever the number of channels involved. Our fast MC (FMC) model does not exhibit the drawbacks due to approximations based on stochastic differential equations and the values of spike jitter are comparable to those obtained with the true Markovian method. In fact, we show here, that these drawbacks can be highlighted in the approximation based on stochastic differential equation methods even for a high number of channels (standard deviation of the 5th spike is about two-fold larger than that of MCF or true Markovian method for 5000 sodium channels). The FMC model appears therefore as the most accurate method to simulate channel noise with a fast execution time that does not depend on the channel number.
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Nsasra E, Peretz G, Orr I, Yifrach O. Regulating Shaker Kv channel clustering by hetero-oligomerization. Front Mol Biosci 2023; 9:1050942. [PMID: 36699695 PMCID: PMC9868669 DOI: 10.3389/fmolb.2022.1050942] [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: 09/22/2022] [Accepted: 12/19/2022] [Indexed: 01/11/2023] Open
Abstract
Scaffold protein-mediated voltage-dependent ion channel clustering at unique membrane sites, such as nodes of Ranvier or the post-synaptic density plays an important role in determining action potential properties and information coding. Yet, the mechanism(s) by which scaffold protein-ion channel interactions lead to channel clustering and how cluster ion channel density is regulated are mostly unknown. This molecular-cellular gap in understanding channel clustering can be bridged in the case of the prototypical Shaker voltage-activated potassium channel (Kv), as the mechanism underlying the interaction of this channel with its PSD-95 scaffold protein partner is known. According to this mechanism, changes in the length of the intrinsically disordered channel C-terminal chain, brought about by alternative splicing to yield the short A and long B chain subunit variants, dictate affinity to PSD-95 and further controls cluster homo-tetrameric Kv channel density. These results raise the hypothesis that heteromeric subunit assembly serves as a means to regulate Kv channel clustering. Since both clustering variants are expressed in similar fly tissues, it is reasonable to assume that hetero-tetrameric channels carrying different numbers of high- (A) and low-affinity (B) subunits could assemble, thereby giving rise to distinct cluster Kv channel densities. Here, we tested this hypothesis using high-resolution microscopy, combined with quantitative clustering analysis. Our results reveal that the A and B clustering variants can indeed assemble to form heteromeric channels and that controlling the number of the high-affinity A subunits within the hetero-oligomer modulates cluster Kv channel density. The implications of these findings for electrical signaling are discussed.
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Diversification of Potassium Currents in Excitable Cells via Kvβ Proteins. Cells 2022; 11:cells11142230. [PMID: 35883673 PMCID: PMC9317154 DOI: 10.3390/cells11142230] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2022] [Revised: 07/09/2022] [Accepted: 07/12/2022] [Indexed: 12/10/2022] Open
Abstract
Excitable cells of the nervous and cardiovascular systems depend on an assortment of plasmalemmal potassium channels to control diverse cellular functions. Voltage-gated potassium (Kv) channels are central to the feedback control of membrane excitability in these processes due to their activation by depolarized membrane potentials permitting K+ efflux. Accordingly, Kv currents are differentially controlled not only by numerous cellular signaling paradigms that influence channel abundance and shape voltage sensitivity, but also by heteromeric configurations of channel complexes. In this context, we discuss the current knowledge related to how intracellular Kvβ proteins interacting with pore complexes of Shaker-related Kv1 channels may establish a modifiable link between excitability and metabolic state. Past studies in heterologous systems have indicated roles for Kvβ proteins in regulating channel stability, trafficking, subcellular targeting, and gating. More recent works identifying potential in vivo physiologic roles are considered in light of these earlier studies and key gaps in knowledge to be addressed by future research are described.
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Dixon RE, Navedo MF, Binder MD, Santana LF. Mechanisms and Physiological Implications of Cooperative Gating of Ion Channels Clusters. Physiol Rev 2021; 102:1159-1210. [PMID: 34927454 DOI: 10.1152/physrev.00022.2021] [Citation(s) in RCA: 33] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Ion channels play a central role in the regulation of nearly every cellular process. Dating back to the classic 1952 Hodgkin-Huxley model of the generation of the action potential, ion channels have always been thought of as independent agents. A myriad of recent experimental findings exploiting advances in electrophysiology, structural biology, and imaging techniques, however, have posed a serious challenge to this long-held axiom as several classes of ion channels appear to open and close in a coordinated, cooperative manner. Ion channel cooperativity ranges from variable-sized oligomeric cooperative gating in voltage-gated, dihydropyridine-sensitive Cav1.2 and Cav1.3 channels to obligatory dimeric assembly and gating of voltage-gated Nav1.5 channels. Potassium channels, transient receptor potential channels, hyperpolarization cyclic nucleotide-activated channels, ryanodine receptors (RyRs), and inositol trisphosphate receptors (IP3Rs) have also been shown to gate cooperatively. The implications of cooperative gating of these ion channels range from fine tuning excitation-contraction coupling in muscle cells to regulating cardiac function and vascular tone, to modulation of action potential and conduction velocity in neurons and cardiac cells, and to control of pace-making activity in the heart. In this review, we discuss the mechanisms leading to cooperative gating of ion channels, their physiological consequences and how alterations in cooperative gating of ion channels may induce a range of clinically significant pathologies.
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Affiliation(s)
- Rose Ellen Dixon
- Department of Physiology and Membrane Biology, University of California, Davis, CA, United States
| | - Manuel F Navedo
- Department of Pharmacology, University of California, Davis, CA, United States
| | - Marc D Binder
- Department of Physiology and Biophysics, University of Washington, Seattle, WA, United States
| | - L Fernando Santana
- Department of Physiology and Membrane Biology, University of California, Davis, CA, United States
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