1
|
Trus M, Atlas D. Non-ionotropic voltage-gated calcium channel signaling. Channels (Austin) 2024; 18:2341077. [PMID: 38601983 PMCID: PMC11017947 DOI: 10.1080/19336950.2024.2341077] [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: 02/09/2024] [Accepted: 04/04/2024] [Indexed: 04/12/2024] Open
Abstract
Voltage-gated calcium channels (VGCCs) are the major conduits for calcium ions (Ca2+) within excitable cells. Recent studies have highlighted the non-ionotropic functionality of VGCCs, revealing their capacity to activate intracellular pathways independently of ion flow. This non-ionotropic signaling mode plays a pivotal role in excitation-coupling processes, including gene transcription through excitation-transcription (ET), synaptic transmission via excitation-secretion (ES), and cardiac contraction through excitation-contraction (EC). However, it is noteworthy that these excitation-coupling processes require extracellular calcium (Ca2+) and Ca2+ occupancy of the channel ion pore. Analogous to the "non-canonical" characterization of the non-ionotropic signaling exhibited by the N-methyl-D-aspartate receptor (NMDA), which requires extracellular Ca2+ without the influx of ions, VGCC activation requires depolarization-triggered conformational change(s) concomitant with Ca2+ binding to the open channel. Here, we discuss the contributions of VGCCs to ES, ET, and EC coupling as Ca2+ binding macromolecules that transduces external stimuli to intracellular input prior to elevating intracellular Ca2+. We emphasize the recognition of calcium ion occupancy within the open ion-pore and its contribution to the excitation coupling processes that precede the influx of calcium. The non-ionotropic activation of VGCCs, triggered by the upstroke of an action potential, provides a conceptual framework to elucidate the mechanistic aspects underlying the microseconds nature of synaptic transmission, cardiac contractility, and the rapid induction of first-wave genes.
Collapse
Affiliation(s)
- Michael Trus
- Department of Biological Chemistry, Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Daphne Atlas
- Department of Biological Chemistry, Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
| |
Collapse
|
2
|
Hernandez-Hernandez G, O'Dwyer SC, Yang PC, Matsumoto C, Tieu M, Fong Z, Lewis TJ, Santana LF, Clancy CE. A computational model predicts sex-specific responses to calcium channel blockers in mammalian mesenteric vascular smooth muscle. eLife 2024; 12:RP90604. [PMID: 38335126 PMCID: PMC10942543 DOI: 10.7554/elife.90604] [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] [Indexed: 02/12/2024] Open
Abstract
The function of the smooth muscle cells lining the walls of mammalian systemic arteries and arterioles is to regulate the diameter of the vessels to control blood flow and blood pressure. Here, we describe an in silico model, which we call the 'Hernandez-Hernandez model', of electrical and Ca2+ signaling in arterial myocytes based on new experimental data indicating sex-specific differences in male and female arterial myocytes from murine resistance arteries. The model suggests the fundamental ionic mechanisms underlying membrane potential and intracellular Ca2+ signaling during the development of myogenic tone in arterial blood vessels. Although experimental data suggest that KV1.5 channel currents have similar amplitudes, kinetics, and voltage dependencies in male and female myocytes, simulations suggest that the KV1.5 current is the dominant current regulating membrane potential in male myocytes. In female cells, which have larger KV2.1 channel expression and longer time constants for activation than male myocytes, predictions from simulated female myocytes suggest that KV2.1 plays a primary role in the control of membrane potential. Over the physiological range of membrane potentials, the gating of a small number of voltage-gated K+ channels and L-type Ca2+ channels are predicted to drive sex-specific differences in intracellular Ca2+ and excitability. We also show that in an idealized computational model of a vessel, female arterial smooth muscle exhibits heightened sensitivity to commonly used Ca2+ channel blockers compared to male. In summary, we present a new model framework to investigate the potential sex-specific impact of antihypertensive drugs.
Collapse
Affiliation(s)
| | - Samantha C O'Dwyer
- Department of Physiology & Membrane Biology, University of California, DavisDavisUnited States
| | - Pei-Chi Yang
- Department of Physiology & Membrane Biology, University of California, DavisDavisUnited States
| | - Collin Matsumoto
- Department of Physiology & Membrane Biology, University of California, DavisDavisUnited States
| | - Mindy Tieu
- Department of Physiology & Membrane Biology, University of California, DavisDavisUnited States
| | - Zhihui Fong
- Department of Physiology & Membrane Biology, University of California, DavisDavisUnited States
| | - Timothy J Lewis
- Department of Mathematics, University of California, DavisDavisUnited States
| | - L Fernando Santana
- Department of Physiology & Membrane Biology, University of California, DavisDavisUnited States
| | - Colleen E Clancy
- Department of Physiology & Membrane Biology, University of California, DavisDavisUnited States
- Center for Precision Medicine and Data Sciences, University of California, DavisDavisUnited States
| |
Collapse
|
3
|
Hernandez-Hernandez G, O’Dwyer SC, Matsumoto C, Tieu M, Fong Z, Yang PC, Lewis TJ, Fernando Santana L, Clancy CE. A computational model predicts sex-specific responses to calcium channel blockers in mammalian mesenteric vascular smooth muscle. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2023.06.24.546394. [PMID: 37425682 PMCID: PMC10327109 DOI: 10.1101/2023.06.24.546394] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/11/2023]
Abstract
The function of the smooth muscle cells lining the walls of mammalian systemic arteries and arterioles is to regulate the diameter of the vessels to control blood flow and blood pressure. Here, we describe an in-silico model, which we call the "Hernandez-Hernandez model", of electrical and C a 2+ signaling in arterial myocytes based on new experimental data indicating sex-specific differences in male and female arterial myocytes from murine resistance arteries. The model suggests the fundamental ionic mechanisms underlying membrane potential and intracellular C a 2+ signaling during the development of myogenic tone in arterial blood vessels. Although experimental data suggest that KV1.5 channel currents have similar amplitudes, kinetics, and voltage dependencies in male and female myocytes, simulations suggest that the KV1.5 current is the dominant current regulating membrane potential in male myocytes. In female cells, which have larger KV2.1 channel expression and longer time constants for activation than male myocytes, predictions from simulated female myocytes suggest that KV2.1 plays a primary role in the control of membrane potential. Over the physiological range of membrane potentials, the gating of a small number of voltage-gated K+ channels and L-type C a 2+ channels are predicted to drive sex-specific differences in intracellular C a 2+ and excitability. We also show that in an idealized computational model of a vessel, female arterial smooth muscle exhibits heightened sensitivity to commonly used C a 2+ channel blockers compared to male. In summary, we present a new model framework to investigate the potential sex-specific impact of anti-hypertensive drugs.
Collapse
Affiliation(s)
- Gonzalo Hernandez-Hernandez
- Department of Physiology & Membrane Biology, Center for Precision Medicine and Data Science, University of California School of Medicine, Davis, California, 95616
- Department of Mathematics, University of California, Davis, California, 95616
| | - Samantha C. O’Dwyer
- Department of Physiology & Membrane Biology, Center for Precision Medicine and Data Science, University of California School of Medicine, Davis, California, 95616
- Department of Mathematics, University of California, Davis, California, 95616
| | - Collin Matsumoto
- Department of Physiology & Membrane Biology, Center for Precision Medicine and Data Science, University of California School of Medicine, Davis, California, 95616
- Department of Mathematics, University of California, Davis, California, 95616
| | - Mindy Tieu
- Department of Physiology & Membrane Biology, Center for Precision Medicine and Data Science, University of California School of Medicine, Davis, California, 95616
- Department of Mathematics, University of California, Davis, California, 95616
| | - Zhihui Fong
- Department of Physiology & Membrane Biology, Center for Precision Medicine and Data Science, University of California School of Medicine, Davis, California, 95616
- Department of Mathematics, University of California, Davis, California, 95616
| | - Pei-Chi Yang
- Department of Physiology & Membrane Biology, Center for Precision Medicine and Data Science, University of California School of Medicine, Davis, California, 95616
- Department of Mathematics, University of California, Davis, California, 95616
| | - Timothy J. Lewis
- Department of Mathematics, University of California, Davis, California, 95616
| | | | - Colleen E. Clancy
- Department of Physiology & Membrane Biology, Center for Precision Medicine and Data Science, University of California School of Medicine, Davis, California, 95616
| |
Collapse
|
4
|
Sanders KM, Santana LF, Baker SA. Interstitial cells of Cajal - pacemakers of the gastrointestinal tract. J Physiol 2023. [PMID: 37997170 DOI: 10.1113/jp284745] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2023] [Accepted: 11/06/2023] [Indexed: 11/25/2023] Open
Abstract
Gastrointestinal (GI) organs display spontaneous, non-neurogenic electrical, and mechanical rhythmicity that underlies fundamental motility patterns, such as peristalsis and segmentation. Electrical rhythmicity (aka slow waves) results from pacemaker activity generated by interstitial cells of Cajal (ICC). ICC express a unique set of ionic conductances and Ca2+ handling mechanisms that generate and actively propagate slow waves. GI smooth muscle cells lack these conductances. Slow waves propagate actively within ICC networks and conduct electrotonically to smooth muscle cells via gap junctions. Slow waves depolarize smooth muscle cells and activate voltage-dependent Ca2+ channels (predominantly CaV1.2), causing Ca2+ influx and excitation-contraction coupling. The main conductances responsible for pacemaker activity in ICC are ANO1, a Ca2+ -activated Cl- conductance, and CaV3.2. The pacemaker cycle, as currently understood, begins with spontaneous, localized Ca2+ release events in ICC that activate spontaneous transient inward currents due to activation of ANO1 channels. Depolarization activates CaV 3.2 channels, causing the upstroke depolarization phase of slow waves. The upstroke is transient and followed by a long-duration plateau phase that can last for several seconds. The plateau phase results from Ca2+ -induced Ca2+ release and a temporal cluster of localized Ca2+ transients in ICC that sustains activation of ANO1 channels and clamps membrane potential near the equilibrium potential for Cl- ions. The plateau phase ends, and repolarization occurs, when Ca2+ stores are depleted, Ca2+ release ceases and ANO1 channels deactivate. This review summarizes key mechanisms responsible for electrical rhythmicity in gastrointestinal organs.
Collapse
Affiliation(s)
- Kenton M Sanders
- Department of Physiology and Cell Biology, School of Medicine, University of Nevada, Reno, NV, USA
| | - L Fernando Santana
- Department of Physiology and Membrane Biology, University of California, Davis, CA, USA
| | - Salah A Baker
- Department of Physiology and Cell Biology, School of Medicine, University of Nevada, Reno, NV, USA
| |
Collapse
|
5
|
Matsumoto C, O'Dwyer SC, Manning D, Hernandez-Hernandez G, Rhana P, Fong Z, Sato D, Clancy CE, Vierra NC, Trimmer JS, Fernando Santana L. The formation of K V2.1 macro-clusters is required for sex-specific differences in L-type Ca V1.2 clustering and function in arterial myocytes. Commun Biol 2023; 6:1165. [PMID: 37963972 PMCID: PMC10645748 DOI: 10.1038/s42003-023-05527-1] [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: 07/03/2023] [Accepted: 10/31/2023] [Indexed: 11/16/2023] Open
Abstract
In arterial myocytes, the canonical function of voltage-gated CaV1.2 and KV2.1 channels is to induce myocyte contraction and relaxation through their responses to membrane depolarization, respectively. Paradoxically, KV2.1 also plays a sex-specific role by promoting the clustering and activity of CaV1.2 channels. However, the impact of KV2.1 protein organization on CaV1.2 function remains poorly understood. We discovered that KV2.1 forms micro-clusters, which can transform into large macro-clusters when a critical clustering site (S590) in the channel is phosphorylated in arterial myocytes. Notably, female myocytes exhibit greater phosphorylation of S590, and macro-cluster formation compared to males. Contrary to current models, the activity of KV2.1 channels seems unrelated to density or macro-clustering in arterial myocytes. Disrupting the KV2.1 clustering site (KV2.1S590A) eliminated KV2.1 macro-clustering and sex-specific differences in CaV1.2 cluster size and activity. We propose that the degree of KV2.1 clustering tunes CaV1.2 channel function in a sex-specific manner in arterial myocytes.
Collapse
Affiliation(s)
- Collin Matsumoto
- Department of Physiology and Membrane Biology, School of Medicine, University of California, Davis, CA, USA
| | - Samantha C O'Dwyer
- Department of Physiology and Membrane Biology, School of Medicine, University of California, Davis, CA, USA
| | - Declan Manning
- Department of Physiology and Membrane Biology, School of Medicine, University of California, Davis, CA, USA
| | | | - Paula Rhana
- Department of Physiology and Membrane Biology, School of Medicine, University of California, Davis, CA, USA
| | - Zhihui Fong
- Department of Physiology and Membrane Biology, School of Medicine, University of California, Davis, CA, USA
| | - Daisuke Sato
- Department of Pharmacology, School of Medicine, University of California, Davis, CA, USA
| | - Colleen E Clancy
- Department of Physiology and Membrane Biology, School of Medicine, University of California, Davis, CA, USA
| | - Nicholas C Vierra
- Department of Physiology and Membrane Biology, School of Medicine, University of California, Davis, CA, USA
| | - James S Trimmer
- Department of Physiology and Membrane Biology, School of Medicine, University of California, Davis, CA, USA
| | - L Fernando Santana
- Department of Physiology and Membrane Biology, School of Medicine, University of California, Davis, CA, USA.
| |
Collapse
|
6
|
Matsumoto C, O'Dwyer SC, Manning D, Hernandez-Hernandez G, Rhana P, Fong Z, Sato D, Clancy CE, Vierra NC, Trimmer JS, Santana LF. The formation of K V 2.1 macro-clusters is required for sex-specific differences in L-type Ca V 1.2 clustering and function in arterial myocytes. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.06.27.546725. [PMID: 37425816 PMCID: PMC10327069 DOI: 10.1101/2023.06.27.546725] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/11/2023]
Abstract
In arterial myocytes, the canonical function of voltage-gated Ca V 1.2 and K V 2.1 channels is to induce myocyte contraction and relaxation through their responses to membrane depolarization, respectively. Paradoxically, K V 2.1 also plays a sex-specific role by promoting the clustering and activity of Ca V 1.2 channels. However, the impact of K V 2.1 protein organization on Ca V 1.2 function remains poorly understood. We discovered that K V 2.1 forms micro-clusters, which can transform into large macro-clusters when a critical clustering site (S590) in the channel is phosphorylated in arterial myocytes. Notably, female myocytes exhibit greater phosphorylation of S590, and macro-cluster formation compared to males. Contrary to current models, the activity of K V 2.1 channels seems unrelated to density or macro-clustering in arterial myocytes. Disrupting the K V 2.1 clustering site (K V 2.1 S590A ) eliminated K V 2.1 macro-clustering and sex-specific differences in Ca V 1.2 cluster size and activity. We propose that the degree of K V 2.1 clustering tunes Ca V 1.2 channel function in a sex-specific manner in arterial myocytes.
Collapse
|
7
|
Manfra O, Louey S, Jonker SS, Perdreau-Dahl H, Frisk M, Giraud GD, Thornburg KL, Louch WE. Augmenting workload drives T-tubule assembly in developing cardiomyocytes. J Physiol 2023:10.1113/JP284538. [PMID: 37128962 PMCID: PMC10854476 DOI: 10.1113/jp284538] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2023] [Accepted: 04/11/2023] [Indexed: 05/03/2023] Open
Abstract
Contraction of cardiomyocytes is initiated at subcellular elements called dyads, where L-type Ca2+ channels in t-tubules are located within close proximity to ryanodine receptors in the sarcoplasmic reticulum. While evidence from small rodents indicates that dyads are assembled gradually in the developing heart, it is unclear how this process occurs in large mammals. We presently examined dyadic formation in fetal and newborn sheep (Ovis aries), and the regulation of this process by fetal cardiac workload. By employing advanced imaging methods, we demonstrated that t-tubule growth and dyadic assembly proceed gradually during fetal sheep development, from 93 days of gestational age until birth (147 days). This process parallels progressive increases in fetal systolic blood pressure, and includes step-wise colocalization of L-type Ca2+ channels and the Na+ /Ca2+ exchanger with ryanodine receptors. These proteins are upregulated together with the dyadic anchor junctophilin-2 during development, alongside changes in the expression of amphiphysin-2 (BIN1) and its partner proteins myotubularin and dynamin-2. Increasing fetal systolic load by infusing plasma or occluding the post-ductal aorta accelerated t-tubule growth. Conversely, reducing fetal systolic load with infusion of enalaprilat, an angiotensin converting enzyme inhibitor, blunted t-tubule formation. Interestingly, altered t-tubule densities did not relate to changes in dyadic junctions, or marked changes in the expression of dyadic regulatory proteins, indicating that distinct signals are responsible for maturation of the sarcoplasmic reticulum. In conclusion, augmenting blood pressure and workload during normal fetal development critically promotes t-tubule growth, while additional signals contribute to dyadic assembly. KEY POINTS: T-tubule growth and dyadic assembly proceed gradually in cardiomyocytes during fetal sheep development, from 93 days of gestational age until the post-natal stage. Increasing fetal systolic load by infusing plasma or occluding the post-ductal aorta accelerated t-tubule growth and hypertrophy. In contrast, reducing fetal systolic load by enalaprilat infusion slowed t-tubule development and decreased cardiomyocyte size. Load-dependent modulation of t-tubule maturation was linked to altered expression patterns of the t-tubule regulatory proteins junctophilin-2 and amphiphysin-2 (BIN1) and its protein partners. Altered t-tubule densities did not influence dyadic formation, indicating that distinct signals are responsible for maturation of the sarcoplasmic reticulum.
Collapse
Affiliation(s)
- Ornella Manfra
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway
- K.G. Jebsen Centre for Cardiac Research, University of Oslo, Oslo, Norway
- Center for Developmental Health, Knight Cardiovascular Institute, Oregon Health and Science University, Portland, OR, USA
| | - Samantha Louey
- Center for Developmental Health, Knight Cardiovascular Institute, Oregon Health and Science University, Portland, OR, USA
- Department of Chemical Physiology and Biochemistry, Oregon Health and Science University, OR, USA
| | - Sonnet S Jonker
- Center for Developmental Health, Knight Cardiovascular Institute, Oregon Health and Science University, Portland, OR, USA
- Department of Chemical Physiology and Biochemistry, Oregon Health and Science University, OR, USA
| | - Harmonie Perdreau-Dahl
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway
- K.G. Jebsen Centre for Cardiac Research, University of Oslo, Oslo, Norway
| | - Michael Frisk
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway
- K.G. Jebsen Centre for Cardiac Research, University of Oslo, Oslo, Norway
| | - George D Giraud
- Center for Developmental Health, Knight Cardiovascular Institute, Oregon Health and Science University, Portland, OR, USA
- Department of Chemical Physiology and Biochemistry, Oregon Health and Science University, OR, USA
- VA Portland Health Care System Portland, OR, USA
| | - Kent L Thornburg
- Center for Developmental Health, Knight Cardiovascular Institute, Oregon Health and Science University, Portland, OR, USA
- Department of Chemical Physiology and Biochemistry, Oregon Health and Science University, OR, USA
| | - William E Louch
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway
- K.G. Jebsen Centre for Cardiac Research, University of Oslo, Oslo, Norway
| |
Collapse
|
8
|
Dixon RE, Trimmer JS. Endoplasmic Reticulum-Plasma Membrane Junctions as Sites of Depolarization-Induced Ca 2+ Signaling in Excitable Cells. Annu Rev Physiol 2023; 85:217-243. [PMID: 36202100 PMCID: PMC9918718 DOI: 10.1146/annurev-physiol-032122-104610] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Membrane contact sites between endoplasmic reticulum (ER) and plasma membrane (PM), or ER-PM junctions, are found in all eukaryotic cells. In excitable cells they play unique roles in organizing diverse forms of Ca2+ signaling as triggered by membrane depolarization. ER-PM junctions underlie crucial physiological processes such as excitation-contraction coupling, smooth muscle contraction and relaxation, and various forms of activity-dependent signaling and plasticity in neurons. In many cases the structure and molecular composition of ER-PM junctions in excitable cells comprise important regulatory feedback loops linking depolarization-induced Ca2+ signaling at these sites to the regulation of membrane potential. Here, we describe recent findings on physiological roles and molecular composition of native ER-PM junctions in excitable cells. We focus on recent studies that provide new insights into canonical forms of depolarization-induced Ca2+ signaling occurring at junctional triads and dyads of striated muscle, as well as the diversity of ER-PM junctions in these cells and in smooth muscle and neurons.
Collapse
Affiliation(s)
- Rose E Dixon
- Department of Physiology and Membrane Biology, School of Medicine, University of California, Davis, California, USA;
| | - James S Trimmer
- Department of Physiology and Membrane Biology, School of Medicine, University of California, Davis, California, USA;
| |
Collapse
|
9
|
Maltsev VA, Stern MD. The paradigm shift: Heartbeat initiation without "the pacemaker cell". Front Physiol 2022; 13:1090162. [PMID: 36569749 PMCID: PMC9780451 DOI: 10.3389/fphys.2022.1090162] [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: 11/05/2022] [Accepted: 11/23/2022] [Indexed: 12/13/2022] Open
Abstract
The current dogma about the heartbeat origin is based on "the pacemaker cell," a specialized cell residing in the sinoatrial node (SAN) that exhibits spontaneous diastolic depolarization triggering rhythmic action potentials (APs). Recent high-resolution imaging, however, demonstrated that Ca signals and APs in the SAN are heterogeneous, with many cells generating APs of different rates and rhythms or even remaining non-firing (dormant cells), i.e., generating only subthreshold signals. Here we numerically tested a hypothesis that a community of dormant cells can generate normal automaticity, i.e., "the pacemaker cell" is not required to initiate rhythmic cardiac impulses. Our model includes 1) non-excitable cells generating oscillatory local Ca releases and 2) an excitable cell lacking automaticity. While each cell in isolation was not "the pacemaker cell", the cell system generated rhythmic APs: The subthreshold signals of non-excitable cells were transformed into respective membrane potential oscillations via electrogenic Na/Ca exchange and further transferred and integrated (computed) by the excitable cells to reach its AP threshold, generating rhythmic pacemaking. Cardiac impulse is an emergent property of the SAN cellular network and can be initiated by cells lacking intrinsic automaticity. Cell heterogeneity, weak coupling, subthreshold signals, and their summation are critical properties of the new pacemaker mechanism, i.e., cardiac pacemaker can operate via a signaling process basically similar to that of "temporal summation" happening in a neuron with input from multiple presynaptic cells. The new mechanism, however, does not refute the classical pacemaker cell-based mechanism: both mechanisms can co-exist and interact within SAN tissue.
Collapse
|
10
|
Wirth AN, Tsutsui K, Maltsev VA, Lakatta EG. Adenosine reduces sinoatrial node cell action potential firing rate by uncoupling its membrane and calcium clocks. Front Physiol 2022; 13:977807. [PMID: 36505046 PMCID: PMC9730041 DOI: 10.3389/fphys.2022.977807] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2022] [Accepted: 11/01/2022] [Indexed: 11/25/2022] Open
Abstract
The spontaneous action potential (AP) firing rate of sinoatrial nodal cells (SANC) is regulated by a system of intracellular Ca2+ and membrane ion current clocks driven by Ca2+-calmodulin-activated adenylyl cyclase-protein kinase-A signaling. The mean AP-cycle length (APCL) and APCL variability inform on the effectiveness of clock coupling. Endogenous ATP metabolite adenosine binds to adenosine receptors (A1, A3) that couple to Gi protein-coupled receptors, reducing spontaneous AP firing rate via Gβγ signaling that activates IKAch,Ado. Adenosine also inhibits adenylyl cyclase activity via Gαi signaling, impacting cAMP-mediated protein kinase-A-dependent protein phosphorylation. We hypothesize that in addition to IKAch,Ado activation, adenosine impacts also Ca2+ via Gαi signaling and that both effects reduce AP firing rate by reducing the effectiveness of the Ca2+ and membrane clock coupling. To this end, we measured Ca2+ and membrane potential characteristics in enzymatically isolated single rabbit SANC. 10 µM adenosine substantially increased both the mean APCL (on average by 43%, n = 10) and AP beat-to-beat variability from 5.1 ± 1.7% to 7.2 ± 2.0% (n = 10) measured via membrane potential and 5.0 ± 2.2% to 10.6 ± 5.9% (n = 40) measured via Ca2+ (assessed as the coefficient of variability = SD/mean). These effects were mediated by hyperpolarization of the maximum diastolic membrane potential (membrane clock effect) and suppression of diastolic local Ca2+releases (LCRs) (Ca2+-clock effect): as LCR size distributions shifted to smaller values, the time of LCR occurrence during diastolic depolarization (LCR period) became prolonged, and the ensemble LCR signal became reduced. The tight linear relationship of coupling between LCR period to the APCL in the presence of adenosine "drifted" upward and leftward, i.e. for a given LCR period, APCL was prolonged, becoming non-linear indicating clock uncoupling. An extreme case of uncoupling occurred at higher adenosine concentrations (>100 µM): small stochastic LCRs failed to self-organize and synchronize to the membrane clock, thus creating a failed attempt to generate an AP resulting in arrhythmia and cessation of AP firing. Thus, the effects of adenosine to activate Gβγ and IKACh,Ado and to activate Gαi, suppressing adenylyl cyclase activity, both contribute to the adenosine-induced increase in the mean APCL and APCL variability by reducing the fidelity of clock coupling and AP firing rate.
Collapse
|
11
|
Grainger N, Santana LF. The Central Brain of the Heart: The Sinoatrial Node. JACC Clin Electrophysiol 2022; 8:1216-1218. [PMID: 36265996 PMCID: PMC10031656 DOI: 10.1016/j.jacep.2022.08.016] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2022] [Accepted: 08/22/2022] [Indexed: 11/06/2022]
Affiliation(s)
- Nathan Grainger
- Department of Physiology and Cell Biology, University of Nevada, Reno School of Medicine, Reno, Nevada, USA.
| | - L Fernando Santana
- Department of Physiology and Membrane Biology, University of California-Davis, Davis, California, USA.
| |
Collapse
|
12
|
Maltsev AV, Stern MD, Maltsev VA. Disorder in Ca2+ release unit locations confers robustness but cuts flexibility of heart pacemaking. J Gen Physiol 2022; 154:213390. [PMID: 35943725 PMCID: PMC9366202 DOI: 10.1085/jgp.202113061] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2021] [Revised: 05/04/2022] [Accepted: 06/21/2022] [Indexed: 12/12/2022] Open
Abstract
Excitation-contraction coupling kinetics is dictated by the action potential rate of sinoatrial-nodal cells. These cells generate local Ca releases (LCRs) that activate Na/Ca exchanger current, which accelerates diastolic depolarization and determines the pace. LCRs are generated by clusters of ryanodine receptors, Ca release units (CRUs), residing in the sarcoplasmic reticulum. While CRU distribution exhibits substantial heterogeneity, its functional importance remains unknown. Using numerical modeling, here we show that with a square lattice distribution of CRUs, Ca-induced-Ca-release propagation during diastolic depolarization is insufficient for pacemaking within a broad range of realistic ICaL densities. Allowing each CRU to deviate randomly from its lattice position allows sparks to propagate, as observed experimentally. As disorder increases, the CRU distribution exhibits larger empty spaces and simultaneously CRU clusters, as in Poisson clumping. Propagating within the clusters, Ca release becomes synchronized, increasing action potential rate and reviving pacemaker function of dormant/nonfiring cells. However, cells with fully disordered CRU positions could not reach low firing rates and their β-adrenergic-receptor stimulation effect was substantially decreased. Inclusion of Cav1.3, a low-voltage activation L-type Ca channel isoform into ICaL, strongly increases recruitment of CRUs to fire during diastolic depolarization, increasing robustness of pacemaking and complementing effects of CRU distribution. Thus, order/disorder in CRU locations along with Cav1.3 expression regulates pacemaker function via synchronization of CRU firing. Excessive CRU disorder and/or overexpression of Cav1.3 boosts pacemaker function in the basal state, but limits the rate range, which may contribute to heart rate range decline with age and disease.
Collapse
Affiliation(s)
- Anna V. Maltsev
- School of Mathematics, Queen Mary University of London, London, UK,Correspondence to Anna V. Maltsev:
| | - Michael D. Stern
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, MD
| | - Victor A. Maltsev
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, MD,Victor A. Maltsev:
| |
Collapse
|