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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.
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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
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Heuser JE. The Structural Basis of Long-Term Potentiation in Hippocampal Synapses, Revealed by Electron Microscopy Imaging of Lanthanum-Induced Synaptic Vesicle Recycling. Front Cell Neurosci 2022; 16:920360. [PMID: 35978856 PMCID: PMC9376242 DOI: 10.3389/fncel.2022.920360] [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: 04/14/2022] [Accepted: 05/05/2022] [Indexed: 11/29/2022] Open
Abstract
Hippocampal neurons in dissociated cell cultures were exposed to the trivalent cation lanthanum for short periods (15–30 min) and prepared for electron microscopy (EM), to evaluate the stimulatory effects of this cation on synaptic ultrastructure. Not only were characteristic ultrastructural changes of exaggerated synaptic vesicle turnover seen within the presynapses of these cultures—including synaptic vesicle depletion and proliferation of vesicle-recycling structures—but the overall architecture of a large proportion of the synapses in the cultures was dramatically altered, due to large postsynaptic “bulges” or herniations into the presynapses. Moreover, in most cases, these postsynaptic herniations or protrusions produced by lanthanum were seen by EM to distort or break or “perforate” the so-called postsynaptic densities (PSDs) that harbor receptors and recognition molecules essential for synaptic function. These dramatic EM observations lead us to postulate that such PSD breakages or “perforations” could very possibly create essential substrates or “tags” for synaptic growth, simply by creating fragmented free edges around the PSDs, into which new receptors and recognition molecules could be recruited more easily, and thus, they could represent the physical substrate for the important synaptic growth process known as “long-term potentiation” (LTP). All of this was created simply in hippocampal dissociated cell cultures, and simply by pushing synaptic vesicle recycling way beyond its normal limits with the trivalent cation lanthanum, but we argued in this report that such fundamental changes in synaptic architecture—given that they can occur at all—could also occur at the extremes of normal neuronal activity, which are presumed to lead to learning and memory.
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Atlas D. Revisiting the molecular basis of synaptic transmission. Prog Neurobiol 2022; 216:102312. [PMID: 35760141 DOI: 10.1016/j.pneurobio.2022.102312] [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: 02/23/2022] [Revised: 06/12/2022] [Accepted: 06/20/2022] [Indexed: 10/17/2022]
Abstract
Measurements of the time elapsed during synaptic transmission has shown that synaptic vesicle (SV) fusion lags behind Ca2+-influx by approximately 60 microseconds (µsec). The conventional model cannot explain this extreme rapidity of the release event. Synaptic transmission occurs at the active zone (AZ), which comprises of two pools of SV, non-releasable "tethered" vesicles, and a readily-releasable pool of channel-associated Ca2+-primed vesicles, "RRP". A recent TIRF study at cerebellar-mossy fiber-terminal, showed that subsequent to an action potential, newly "tethered" vesicles, became fusion-competent in a Ca2+-dependent manner, 300-400 milliseconds after tethering, but were not fused. This time resolution may correspond to priming of tethered vesicles through Ca2+-binding to Syt1/Munc13-1/complexin. It confirms that Ca2+-priming and Ca2+-influx-independent fusion, are two distinct events. Notably, we have established that Ca2+ channel signals evoked-release in an ion flux-independent manner, demonstrated by Ca2+-impermeable channel, or a Ca2+ channel in which Ca2+ is replaced by impermeable La3+. Thus, conformational changes in a channel coupled to RRP appear to directly activate the release machinery and account for a µsec Ca2+-influx-independent vesicle fusion. Rapid vesicle fusion driven by non-ionotropic channel signaling strengthens a conformational-coupling mechanism of synaptic transmission, and contributes to better understanding of neuronal communication vital for brain function.
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Affiliation(s)
- Daphne Atlas
- Dept. of Biological Chemistry, Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, 91904 Israel.
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Moya‐Díaz J, Bayonés L, Montenegro M, Cárdenas AM, Koch H, Doi A, Marengo FD. Ca 2+ -independent and voltage-dependent exocytosis in mouse chromaffin cells. Acta Physiol (Oxf) 2020; 228:e13417. [PMID: 31769918 DOI: 10.1111/apha.13417] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2019] [Revised: 11/19/2019] [Accepted: 11/20/2019] [Indexed: 12/11/2022]
Abstract
AIM It is widely accepted that the exocytosis of synaptic and secretory vesicles is triggered by Ca2+ entry through voltage-dependent Ca2+ channels. However, there is evidence of an alternative mode of exocytosis induced by membrane depolarization but lacking Ca2+ current and intracellular Ca2+ increase. In this work we investigated if such a mechanism contributes to secretory vesicle exocytosis in mouse chromaffin cells. METHODS Exocytosis was evaluated by patch-clamp membrane capacitance measurements, carbon fibre amperometry and TIRF. Cytosolic Ca2+ was estimated using epifluorescence microscopy and fluo-8 (salt form). RESULTS Cells stimulated by brief depolatizations in absence of extracellular Ca+2 show moderate but consistent exocytosis, even in presence of high cytosolic BAPTA concentration and pharmacological inhibition of Ca+2 release from intracellular stores. This exocytosis is tightly dependent on membrane potential, is inhibited by neurotoxin Bont-B (cleaves the v-SNARE synaptobrevin), is very fast (saturates with time constant <10 ms), it is followed by a fast endocytosis sensitive to the application of an anti-dynamin monoclonal antibody, and recovers after depletion in <5 s. Finally, this exocytosis was inhibited by: (i) ω-agatoxin IVA (blocks P/Q-type Ca2+ channel gating), (ii) in cells from knock-out P/Q-type Ca2+ channel mice, and (iii) transfection of free synprint peptide (interferes in P/Q channel-exocytic proteins association). CONCLUSION We demonstrated that Ca2+ -independent and voltage-dependent exocytosis is present in chromaffin cells. This process is tightly coupled to membrane depolarization, and is able to support secretion during action potentials at low basal rates. P/Q-type Ca2+ channels can operate as voltage sensors of this process.
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Affiliation(s)
- José Moya‐Díaz
- Instituto de Fisiología, Biología Molecular y Neurociencias Departamento de Fisiología y Biología Molecular y Celular Facultad de Ciencias Exactas y Naturales Universidad de Buenos AiresConsejo Nacional de Investigaciones Científicas y Técnicas Buenos Aires Argentina
| | - Lucas Bayonés
- Instituto de Fisiología, Biología Molecular y Neurociencias Departamento de Fisiología y Biología Molecular y Celular Facultad de Ciencias Exactas y Naturales Universidad de Buenos AiresConsejo Nacional de Investigaciones Científicas y Técnicas Buenos Aires Argentina
| | - Mauricio Montenegro
- Instituto de Fisiología, Biología Molecular y Neurociencias Departamento de Fisiología y Biología Molecular y Celular Facultad de Ciencias Exactas y Naturales Universidad de Buenos AiresConsejo Nacional de Investigaciones Científicas y Técnicas Buenos Aires Argentina
| | - Ana M. Cárdenas
- Centro Interdisciplinario de Neurociencia de Valparaíso Facultad de Ciencias Universidad de Valparaíso Valparaíso Chile
| | - Henner Koch
- Center for Integrative Brain Research Seattle Children's Research Institute Seattle WA USA
- Department of Neurology and Epileptology Hertie‐Institute for Clinical Brain ResearchUniversity of Tübingen Tübingen Germany
| | - Atsushi Doi
- Department of Rehabilitation Graduate School of Health Science Kumamoto Health Science University Kumamoto Japan
| | - Fernando D. Marengo
- Instituto de Fisiología, Biología Molecular y Neurociencias Departamento de Fisiología y Biología Molecular y Celular Facultad de Ciencias Exactas y Naturales Universidad de Buenos AiresConsejo Nacional de Investigaciones Científicas y Técnicas Buenos Aires Argentina
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5
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Servili E, Trus M, Atlas D. Ion occupancy of the channel pore is critical for triggering excitation-transcription (ET) coupling. Cell Calcium 2019; 84:102102. [DOI: 10.1016/j.ceca.2019.102102] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2019] [Revised: 10/07/2019] [Accepted: 10/07/2019] [Indexed: 11/28/2022]
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Huang CH, Moser T. Ca 2+ Regulates the Kinetics of Synaptic Vesicle Fusion at the Afferent Inner Hair Cell Synapse. Front Cell Neurosci 2018; 12:364. [PMID: 30386210 PMCID: PMC6199957 DOI: 10.3389/fncel.2018.00364] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2018] [Accepted: 09/25/2018] [Indexed: 11/13/2022] Open
Abstract
The early auditory pathway processes information at high rates and with utmost temporal fidelity. Consequently, the synapses in the auditory pathway are highly specialized to meet the extraordinary requirements on signal transmission. The calyceal synapses in the auditory brainstem feature more than a hundred active zones (AZs) with thousands of releasable synaptic vesicles (SVs). In contrast, the first auditory synapse, the afferent synapse of inner hair cells (IHCs) and type I spiral ganglion neurons (SGNs), typically exhibits a single ribbon-type AZ tethering only tens of SVs resulting in a highly stochastic pattern of transmitter release. Spontaneous excitatory postsynaptic currents (sEPSCs), besides more conventional EPSCs with a single peak, fast rise and decay (compact), also include EPSCs with multiple peaks, variable rise and decay times (non-compact). The strong heterogeneity in size and shape of spontaneous EPSCs has led to the hypothesis of multivesicular release (MVR) that is more (compact) or less (non-compact) synchronized by coordination of release sites. Alternatively, univesicular release (UVR), potentially involving glutamate release through a flickering fusion pore for non-compact EPSCs, has been suggested to underlie IHC exocytosis. Here, we further investigated the mode of release by recording sEPSCs from SGNs of hearing rats while manipulating presynaptic IHC Ca2+ influx by changes in extracellular [Ca2+] ([Ca2+]e) and by application of the Ca2+ channel antagonist, isradipine, or the Ca2+ channel agonist, BayK8644 (BayK). Our data reveal that Ca2+ influx manipulation leaves the distributions of sEPSC amplitude and charge largely unchanged. Regardless the type of manipulation, the rate of sEPSC decreased with the reduction in Ca2+ influx. The fraction of compact sEPSCs was increased in the presence of BayK, an effect that was abolished when combined with decreased [Ca2+]e. In conclusion, we propose that UVR is the prevailing mode of exocytosis at cochlear IHCs of hearing rats, whereby the rate of exocytosis and the kinetics of SV fusion are regulated by Ca2+ influx.
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Affiliation(s)
- Chao-Hua Huang
- Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany.,Synaptic Nanophysiology Group, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany.,Collaborative Research Center 889, University of Göttingen, Göttingen, Germany
| | - Tobias Moser
- Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany.,Synaptic Nanophysiology Group, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany.,Collaborative Research Center 889, University of Göttingen, Göttingen, Germany.,Auditory Neuroscience Associated Group, Max Planck Institute for Experimental Medicine, Göttingen, Germany
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β-Subunit of the voltage-gated Ca 2+ channel Cav1.2 drives signaling to the nucleus via H-Ras. Proc Natl Acad Sci U S A 2018; 115:E8624-E8633. [PMID: 30150369 DOI: 10.1073/pnas.1805380115] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Depolarization-induced signaling to the nucleus by the L-type voltage-gated calcium channel Cav1.2 is widely assumed to proceed by elevating intracellular calcium. The apparent lack of quantitative correlation between Ca2+ influx and gene activation suggests an alternative activation pathway. Here, we demonstrate that membrane depolarization of HEK293 cells transfected with α11.2/β2b/α2δ subunits (Cav1.2) triggers c-Fos and MeCP2 activation via the Ras/ERK/CREB pathway. Nuclear signaling is lost either by absence of the intracellular β2 subunit or by transfecting the cells with the channel mutant α11.2W440A/β2b/α2δ, a mutation that disrupts the interaction between α11.2 and β2 subunits. Pulldown assays in neuronal SH-SY5Y cells and in vitro binding of recombinant H-Ras and β2 confirmed the importance of the intracellular β2 subunit for depolarization-induced gene activation. Using a Ca2+-impermeable mutant channel α11.2L745P/β2b/α2δ or disrupting Ca2+/calmodulin binding to the channel using the channel mutant α11.2I1624A/β2b/α2δ, we demonstrate that depolarization-induced c-Fos and MeCP2 activation does not depend on Ca2+ transport by the channel. Thus, in contrast to the paradigm that elevated intracellular Ca2+ drives nuclear signaling, we show that Cav1.2-triggered c-Fos or MeCP2 is dependent on extracellular Ca2+ and Ca2+ occupancy of the open channel pore, but is Ca2+-influx independent. An indispensable β-subunit interaction with H-Ras, which is triggered by conformational changes at α11.2 independently of Ca2+ flux, brings to light a master regulatory role of β2 in transcriptional activation via the ERK/CREB pathway. This mode of H-Ras activation could have broad implications for understanding the coupling of membrane depolarization to the rapid induction of gene transcription.
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Heusinkveld HJ, Westerink RH. Comparison of different in vitro cell models for the assessment of pesticide-induced dopaminergic neurotoxicity. Toxicol In Vitro 2017; 45:81-88. [DOI: 10.1016/j.tiv.2017.07.030] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2017] [Revised: 05/17/2017] [Accepted: 07/29/2017] [Indexed: 01/10/2023]
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9
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Li B, Tadross MR, Tsien RW. Sequential ionic and conformational signaling by calcium channels drives neuronal gene expression. Science 2016; 351:863-7. [PMID: 26912895 DOI: 10.1126/science.aad3647] [Citation(s) in RCA: 78] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Voltage-gated CaV1.2 channels (L-type calcium channel α1C subunits) are critical mediators of transcription-dependent neural plasticity. Whether these channels signal via the influx of calcium ion (Ca(2+)), voltage-dependent conformational change (VΔC), or a combination of the two has thus far been equivocal. We fused CaV1.2 to a ligand-gated Ca(2+)-permeable channel, enabling independent control of localized Ca(2+) and VΔC signals. This revealed an unexpected dual requirement: Ca(2+) must first mobilize actin-bound Ca(2+)/calmodulin-dependent protein kinase II, freeing it for subsequent VΔC-mediated accumulation. Neither signal alone sufficed to activate transcription. Signal order was crucial: Efficiency peaked when Ca(2+) preceded VΔC by 10 to 20 seconds. CaV1.2 VΔC synergistically augmented signaling by N-methyl-d-aspartate receptors. Furthermore, VΔC mistuning correlated with autistic symptoms in Timothy syndrome. Thus, nonionic VΔC signaling is vital to the function of CaV1.2 in synaptic and neuropsychiatric processes.
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Affiliation(s)
- Boxing Li
- Department of Neuroscience and Physiology and New York University Neuroscience Institute, New York, NY 10016, USA
| | - Michael R Tadross
- Department of Molecular and Cellular Physiology, Beckman Center, School of Medicine, Stanford University, Stanford, CA 94305, USA. Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA 20147, USA.
| | - Richard W Tsien
- Department of Neuroscience and Physiology and New York University Neuroscience Institute, New York, NY 10016, USA. Department of Molecular and Cellular Physiology, Beckman Center, School of Medicine, Stanford University, Stanford, CA 94305, USA
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10
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Gianulis EC, Pakhomov AG. Gadolinium modifies the cell membrane to inhibit permeabilization by nanosecond electric pulses. Arch Biochem Biophys 2015; 570:1-7. [PMID: 25707556 DOI: 10.1016/j.abb.2015.02.013] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2015] [Revised: 02/12/2015] [Accepted: 02/16/2015] [Indexed: 11/18/2022]
Abstract
Lanthanide ions are the only known blockers of permeabilization by electric pulses of nanosecond duration (nsEP), but the underlying mechanisms are unknown. We employed timed applications of Gd(3+) before or after nsEP (600-ns, 20 kV/cm) to investigate the mechanism of inhibition, and measured the uptake of the membrane-impermeable YO-PRO-1 (YP) and propidium (Pr) dyes. Gd(3+) inhibited dye uptake in a concentration-dependent manner. The inhibition of Pr uptake was always about 2-fold stronger. Gd(3+) was effective when added after nsEP, as well as when it was present during nsEP exposure and removed afterward. Pores formed by nsEP in the presence of Gd(3+) remained quiescent unless Gd(3+) was promptly washed away. Such pores resealed (or shrunk) shortly after the wash despite the absence of Gd(3+). Finally, a brief (3s) Gd(3+) perfusion was equally potent at inhibiting dye uptake when performed either immediately before or after nsEP, or early before nsEP. The persistent protective effect of Gd(3+) even in its absence proves that inhibition by Gd(3+) does not result from simple pore obstruction. Instead, Gd(3+) causes lasting modification of the membrane, occurring promptly and irrespective of pore presence; it makes the membrane less prone to permeabilization and/or reduces the stability of electropores.
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Affiliation(s)
- Elena C Gianulis
- Frank Reidy Research Center for Bioelectrics, Old Dominion University, Norfolk, VA, 23508, USA.
| | - Andrei G Pakhomov
- Frank Reidy Research Center for Bioelectrics, Old Dominion University, Norfolk, VA, 23508, USA
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11
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Bachnoff N, Cohen-Kutner M, Trus M, Atlas D. Intra-membrane signaling between the voltage-gated Ca2+-channel and cysteine residues of syntaxin 1A coordinates synchronous release. Sci Rep 2014; 3:1620. [PMID: 23567899 PMCID: PMC3621091 DOI: 10.1038/srep01620] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2013] [Accepted: 03/26/2013] [Indexed: 11/28/2022] Open
Abstract
The interaction of syntaxin 1A (Sx1A) with voltage-gated calcium channels (VGCC) is required for depolarization-evoked release. However, it is unclear how the signal is transferred from the channel to the exocytotic machinery and whether assembly of Sx1A and the calcium channel is conformationally linked to triggering synchronous release. Here we demonstrate that depolarization-evoked catecholamine release was decreased in chromaffin cells infected with semliki forest viral vectors encoding Sx1A mutants, Sx1AC271V, or Sx1AC272V, or by direct oxidation of these Sx1A transmembrane (TM) cysteine residues. Mutating or oxidizing these highly conserved Sx1A Cys271 and Cys272 equally disrupted the Sx1A interaction with the channel. The results highlight the functional link between the VGCC and the exocytotic machinery, and attribute the redox sensitivity of the release process to the Sx1A TM C271 and C272. This unique intra-membrane signal-transduction pathway enables fast signaling, and triggers synchronous release by conformational-coupling of the channel with Sx1A.
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Affiliation(s)
- Niv Bachnoff
- The Hebrew University of Jerusalem, Institute of Life Sciences, Department of Biological Chemistry, Givat-Ram, Jerusalem, Israel
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Tola EN, Mungan MT, Uğuz AC, Naziroğlu M. Intracellular Ca2+ and antioxidant values induced positive effect on fertilisation ratio and oocyte quality of granulosa cells in patients undergoing in vitro fertilisation. Reprod Fertil Dev 2014; 25:746-52. [PMID: 22954014 DOI: 10.1071/rd12144] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2012] [Accepted: 06/19/2012] [Indexed: 12/12/2022] Open
Abstract
Oxidative stress is important for promoting oocyte maturation and ovulation within the follicle through calcium ion (Ca(2+)) influx. The relationship between antioxidant and cytosolic Ca(2+) levels and oocyte quality and fertilisation rate in the granulosa cells of patients undergoing in vitro fertilisation was investigated. Granulosa cells were collected from 33 patients. Cytosolic free Ca(2+) ([Ca(2+)]i) concentration, lipid peroxidation, reduced glutathione, glutathione peroxidase and oocyte quality were measured in the granulosa cells. The relationship between two drug protocols was also examined (gonadotrophin-releasing hormone antagonist and agonist protocols) and the same parameters investigated. The [Ca(2+)]i concentration (P<0.001), glutathione (P<0.05) and oocyte quality (P<0.001) values were significantly higher in the fertilised group than in the non-fertilised group, although glutathione peroxidase activity was significantly (P<0.05) higher in the non-fertilised group than in the fertilised group. The [Ca(2+)]i concentrations were also higher (P<0.001) in the good-quality oocyte groups than in the poor-quality oocyte group. There was no correlation between the two drug protocols and investigated parameters. In conclusion, it was observed that high glutathione and cytosolic Ca(2+) concentrations in granulosa cells of patients undergoing in vitro fertilisation tended to increase the fertilisation potential of oocytes.
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Affiliation(s)
- Esra Nur Tola
- Department of Obstetrics and Gynaecology, Faculty of Medicine, Suleyman Demirel University, TR-32260, Isparta, Turkey
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Atlas D. Voltage-gated calcium channels function as Ca2+-activated signaling receptors. Trends Biochem Sci 2014; 39:45-52. [PMID: 24388968 DOI: 10.1016/j.tibs.2013.12.005] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2013] [Revised: 11/24/2013] [Accepted: 12/09/2013] [Indexed: 02/06/2023]
Abstract
Voltage-gated calcium channels (VGCCs) are transmembrane cell surface proteins responsible for multifunctional signals. In response to voltage, VGCCs trigger synaptic transmission, drive muscle contraction, and regulate gene expression. Voltage perturbations open VGCCs enabling Ca(2+) binding to the low affinity Ca(2+) binding site of the channel pore. Subsequent to permeation, Ca(2+) targets selective proteins to activate diverse signaling pathways. It is becoming apparent that the Ca(2+)-bound channel triggers secretion in excitable cells and drives contraction in cardiomyocytes prior to Ca(2+) permeation. Here, I highlight recent data implicating receptor-like function of the Ca(2+)-bound channel in converting external Ca(2+) into an intracellular signal. The two sequential mechanistic perspectives of VGCC function are discussed in the context of the prevailing and long-standing current models of depolarization-evoked secretion and cardiac contraction.
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Affiliation(s)
- Daphne Atlas
- Department of Biological Chemistry, The Alexander Silverman Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, 91904 Israel.
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Atlas D. The Voltage-Gated Calcium Channel Functions as the Molecular Switch of Synaptic Transmission. Annu Rev Biochem 2013; 82:607-35. [DOI: 10.1146/annurev-biochem-080411-121438] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Daphne Atlas
- Department of Biological Chemistry, Institute of Life Sciences, The Hebrew University of Jerusalem, 91904 Jerusalem, Israel;
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Gez LS, Hagalili Y, Shainberg A, Atlas D. Voltage-driven Ca(2+) binding at the L-type Ca(2+) channel triggers cardiac excitation-contraction coupling prior to Ca(2+) influx. Biochemistry 2012; 51:9658-66. [PMID: 23145875 DOI: 10.1021/bi301124a] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The activation of the ryanodine Ca(2+) release channels (RyR2) by the entry of Ca(2+) through the L-type Ca(2+) channels (Cav1.2) is believed to be the primary mechanism of excitation-contraction (EC) coupling in cardiac cells. This proposed mechanism of Ca(2+)-induced Ca(2+) release (CICR) cannot fully account for the lack of a termination signal for this positive feedback process. Using Cav1.2 channel mutants, we demonstrate that the Ca(2+)-impermeable α(1)1.2/L775P/T1066Y mutant introduced through lentiviral infection into neonate cardiomyocytes triggers Ca(2+) transients in a manner independent of Ca(2+) influx. In contrast, the α(1)1.2/L775P/T1066Y/4A mutant, in which the Ca(2+)-binding site of the channel was destroyed, supports neither the spontaneous nor the electrically evoked contractions. Ca(2+) bound at the channel selectivity filter appears to initiate a signal that is conveyed directly from the channel pore to RyR2, triggering contraction of cardiomyocytes prior to Ca(2+) influx. Thus, RyR2 is activated in response to a conformational change in the L-type channel during membrane depolarization and not through interaction with Ca(2+) ions diffusing in the junctional gap space. Accordingly, termination of the RyR2 activity is achieved when the signal stops upon the return of the L-channel to the resting state. We propose a new model in which the physical link between Cav1.2 and RyR2 allows propagation of a conformational change induced at the open pore of the channel to directly activate RyR2. These results highlight Cav1.2 as a signaling protein and provide a mechanism for terminating the release of Ca(2+) from RyR2 through protein-protein interactions. In this model, the L-type channel is a master regulator of both initiation and termination of EC coupling in neonate cardiomyocytes.
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Affiliation(s)
- Liron S Gez
- Department of Biological Chemistry, Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
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16
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Control of low-threshold exocytosis by T-type calcium channels. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2012; 1828:1579-86. [PMID: 22885170 DOI: 10.1016/j.bbamem.2012.07.031] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/18/2012] [Revised: 07/30/2012] [Accepted: 07/30/2012] [Indexed: 12/11/2022]
Abstract
Low-voltage-activated (LVA) T-type Ca²⁺ channels differ from their high-voltage-activated (HVA) homologues by unique biophysical properties. Hence, whereas HVA channels convert action potentials into intracellular Ca²⁺ elevations, T-type channels control Ca²⁺ entry during small depolarizations around the resting membrane potential. They play an important role in electrical activities by generating low-threshold burst discharges that occur during various physiological and pathological forms of neuronal rhythmogenesis. In addition, they mediate a previously unrecognized function in the control of synaptic transmission where they directly trigger the release of neurotransmitters at rest. In this review, we summarize our present knowledge of the role of T-type Ca²⁺ channels in vesicular exocytosis, and emphasize the critical importance of localizing the exocytosis machinery close to the Ca²⁺ source for reliable synaptic transmission. This article is part of a Special Issue entitled: Calcium channels.
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Regulation of voltage-gated calcium channels by synaptic proteins. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2012; 740:759-75. [PMID: 22453968 DOI: 10.1007/978-94-007-2888-2_33] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Calcium entry through neuronal voltage-gated calcium channels into presynaptic nerve terminal is a key step in synaptic exocytosis. In order to receive the calcium signal and trigger fast, efficient and spatially delimited neurotransmitter release, the vesicle-docking/release machinery must be located near the calcium source. In many cases, this close localization is achieved by a direct interaction of several members of the vesicle release machinery with the calcium channels. In turn, the binding of synaptic proteins to presynaptic calcium channels modulates channel activity to provide fine control over calcium entry, and thus modulates synaptic strength. In this chapter we summarize our present knowledge of the molecular mechanisms by which synaptic proteins regulate presynaptic calcium channel activity.
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Xiong W, Liu T, Wang Y, Chen X, Sun L, Guo N, Zheng H, Zheng L, Ruat M, Han W, Zhang CX, Zhou Z. An inhibitory effect of extracellular Ca2+ on Ca2+-dependent exocytosis. PLoS One 2011; 6:e24573. [PMID: 22028769 PMCID: PMC3196490 DOI: 10.1371/journal.pone.0024573] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2011] [Accepted: 08/14/2011] [Indexed: 11/21/2022] Open
Abstract
Aim Neurotransmitter release is elicited by an elevation of intracellular Ca2+ concentration ([Ca2+]i). The action potential triggers Ca2+ influx through Ca2+ channels which causes local changes of [Ca2+]i for vesicle release. However, any direct role of extracellular Ca2+ (besides Ca2+ influx) on Ca2+-dependent exocytosis remains elusive. Here we set out to investigate this possibility on rat dorsal root ganglion (DRG) neurons and chromaffin cells, widely used models for studying vesicle exocytosis. Results Using photolysis of caged Ca2+ and caffeine-induced release of stored Ca2+, we found that extracellular Ca2+ inhibited exocytosis following moderate [Ca2+]i rises (2–3 µM). The IC50 for extracellular Ca2+ inhibition of exocytosis (ECIE) was 1.38 mM and a physiological reduction (∼30%) of extracellular Ca2+ concentration ([Ca2+]o) significantly increased the evoked exocytosis. At the single vesicle level, quantal size and release frequency were also altered by physiological [Ca2+]o. The calcimimetics Mg2+, Cd2+, G418, and neomycin all inhibited exocytosis. The extracellular Ca2+-sensing receptor (CaSR) was not involved because specific drugs and knockdown of CaSR in DRG neurons did not affect ECIE. Conclusion/Significance As an extension of the classic Ca2+ hypothesis of synaptic release, physiological levels of extracellular Ca2+ play dual roles in evoked exocytosis by providing a source of Ca2+ influx, and by directly regulating quantal size and release probability in neuronal cells.
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Affiliation(s)
- Wei Xiong
- State Key Laboratory of Biomembrane Engineering and Center for Life Sciences, Institute of Molecular Medicine, Peking University, Beijing, China
| | - Tao Liu
- State Key Laboratory of Biomembrane Engineering and Center for Life Sciences, Institute of Molecular Medicine, Peking University, Beijing, China
| | - Yeshi Wang
- State Key Laboratory of Biomembrane Engineering and Center for Life Sciences, Institute of Molecular Medicine, Peking University, Beijing, China
| | - Xiaowei Chen
- State Key Laboratory of Biomembrane Engineering and Center for Life Sciences, Institute of Molecular Medicine, Peking University, Beijing, China
| | - Lei Sun
- State Key Laboratory of Biomembrane Engineering and Center for Life Sciences, Institute of Molecular Medicine, Peking University, Beijing, China
| | - Ning Guo
- State Key Laboratory of Biomembrane Engineering and Center for Life Sciences, Institute of Molecular Medicine, Peking University, Beijing, China
| | - Hui Zheng
- State Key Laboratory of Biomembrane Engineering and Center for Life Sciences, Institute of Molecular Medicine, Peking University, Beijing, China
| | - Lianghong Zheng
- State Key Laboratory of Biomembrane Engineering and Center for Life Sciences, Institute of Molecular Medicine, Peking University, Beijing, China
| | - Martial Ruat
- CNRS, UPR9040, Institut de Neurobiologie Alfred Fessard-IFR 2118, Gif sur Yvette, France
| | - Weiping Han
- Laboratory of Metabolic Medicine, Singapore Bioimaging Consortium, Agency for Science, Technology, and Research, Singapore, Singapore
| | - Claire Xi Zhang
- State Key Laboratory of Biomembrane Engineering and Center for Life Sciences, Institute of Molecular Medicine, Peking University, Beijing, China
- * E-mail: (ZZ); (CXZ)
| | - Zhuan Zhou
- State Key Laboratory of Biomembrane Engineering and Center for Life Sciences, Institute of Molecular Medicine, Peking University, Beijing, China
- * E-mail: (ZZ); (CXZ)
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Marom M, Birnbaumer L, Atlas D. Membrane depolarization combined with Gq-activated G-protein-coupled receptors induce transient receptor potential channel 1 (TRPC1)- dependent potentiation of catecholamine release. Neuroscience 2011; 189:132-45. [DOI: 10.1016/j.neuroscience.2011.05.007] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2011] [Revised: 05/02/2011] [Accepted: 05/02/2011] [Indexed: 10/18/2022]
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20
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Bachnoff N, Trus M, Atlas D. Alleviation of oxidative stress by potent and selective thioredoxin-mimetic peptides. Free Radic Biol Med 2011; 50:1355-67. [PMID: 21377525 DOI: 10.1016/j.freeradbiomed.2011.02.026] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/25/2010] [Revised: 01/30/2011] [Accepted: 02/20/2011] [Indexed: 11/19/2022]
Abstract
One of the major enzymatic cell defenses providing protection from oxidative injury is the TrxR-Trx system. It consists of NADPH and thioredoxin reductase (TrxR), which maintain thioredoxin (Trx) in a reduced state. Perturbing the TrxR-Trx system with the selective TrxR inhibitor auranofin (AuF; 2,3,4,6-tetra-O-acetyl-1-thio-β-D-glucopyranosato-S-(triethylphosphine) gold) induces oxidative stress by keeping Trx in its oxidized state. We have prepared a family of tri- and tetra-oligopeptides derived from the canonical CxxC motif of the Trx active site and a modified CxC motif. These Trx-mimetic compounds are N- and C-terminal-blocked peptides that consist of two cysteine residues that flank the two-amino-acid CxxC motif (CB4 and CB6) or the single-amino-acid CxC motif (CB3). Catecholamine (CA) secretion in bovine chromaffin cells, which is a highly redox sensitive process, is abolished by AuF. The Trx-mimetic peptides effectively restore CA secretion, as monitored by amperometry in single cells. They also prevent the AuF-induced phosphorylation of p38 mitogen-activated protein kinase (MAPK) and c-Jun NH2-terminal kinase. In PC12 cells, the alleviation of AuF-induced ERK1/2-MAPK phosphorylation by Trx-like peptides parallels their effect of restoring CA secretion. CB3, CB4, and CB6 act intracellularly and are significantly more potent than the traditional antioxidants NAC, GSH, DTT, AD4 (NAC-amide), and ascorbic acid. Taken together, the CxxC and CxC peptides represent a new family of potent and selective redox compounds that could serve as potential candidates for prevention and treatment of oxidative-stress-related disorders.
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Affiliation(s)
- Niv Bachnoff
- The Institute of Life Sciences, Department of Biological Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
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Bachnoff N, Cohen-Kutner M, Atlas D. The involvement of ser1898 of the human L-type calcium channel in evoked secretion. Int J Endocrinol 2011; 2011:746482. [PMID: 22216029 PMCID: PMC3246732 DOI: 10.1155/2011/746482] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/03/2011] [Accepted: 08/17/2011] [Indexed: 11/18/2022] Open
Abstract
A PKA consensus phosphorylation site S1928 at the α(1)1.2 subunit of the rabbit cardiac L-type channel, Ca(V)1.2, is involved in the regulation of Ca(V)1.2 kinetics and affects catecholamine secretion. This mutation does not alter basal Ca(V)1.2 current properties or regulation of Ca(V)1.2 current by PKA and the beta-adrenergic receptor, but abolishes Ca(V)1.2 phosphorylation by PKA. Here, we test the contribution of the corresponding PKA phosphorylation site of the human α(1)1.2 subunit S1898, to the regulation of catecholamine secretion in bovine chromaffin cells. Chromaffin cells were infected with a Semliki-Forest viral vector containing either the human wt or a mutated S1898A α(1)1.2 subunit. Both subunits harbor a T1036Y mutation conferring nifedipine insensitivity. Secretion evoked by depolarization in the presence of nifedipine was monitored by amperometry. Depolarization-triggered secretion in cells infected with either the wt α(1)1.2 or α(1)1.2/S1898A mutated subunit was elevated to a similar extent by forskolin. Forskolin, known to directly activate adenylyl-cyclase, increased the rate of secretion in a manner that is largely independent of the presence of S1898. Our results are consistent with the involvement of additional PKA regulatory site(s) at the C-tail of α(1)1.2, the pore forming subunit of Ca(V)1.2.
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22
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Weiss N. Control of depolarization-evoked presynaptic neurotransmitter release by Cav2.1 calcium channel: old story, new insights. Channels (Austin) 2010; 4:431-3. [PMID: 20935476 DOI: 10.4161/chan.4.6.13613] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Affiliation(s)
- Norbert Weiss
- INSERM U836, Grenoble Institut des Neurosciences, Grenoble, France.
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Malasics A, Boda D, Valiskó M, Henderson D, Gillespie D. Simulations of calcium channel block by trivalent cations: Gd(3+) competes with permeant ions for the selectivity filter. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2010; 1798:2013-21. [PMID: 20696128 DOI: 10.1016/j.bbamem.2010.08.001] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/30/2009] [Revised: 07/29/2010] [Accepted: 08/02/2010] [Indexed: 10/19/2022]
Abstract
Current through L-type calcium channels (Ca(V)1.2 or dihydropyridine receptor) can be blocked by micromolar concentrations of trivalent cations like the lanthanide gadolinium (Gd(3+)). It has been proposed that trivalent block is due to ions competing for a binding site in both the open and closed configuration, but possibly with different trivalent affinities. Here, we corroborate this general view of trivalent block by computing conductance of a model L-type calcium channel. The model qualitatively reproduces the Gd(3+) concentration dependence and the effect that substantially more Gd(3+) is required to produce similar block in the presence of Sr(2+) (compared to Ba(2+)) and even more in the presence of Ca(2+). Trivalent block is explained in this model by cations binding in the selectivity filter with the charge/space competition mechanism. This is the same mechanism that in the model channel governs other selectivity properties. Specifically, selectivity is determined by the combination of ions that most effectively screen the negative glutamates of the protein while finding space in the midst of the closely packed carboxylate groups of the glutamate residues.
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Affiliation(s)
- Attila Malasics
- Department of Physical Chemistry, University of Pannonia, Veszprém, Hungary
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Atlas D. Signaling role of the voltage-gated calcium channel as the molecular on/off-switch of secretion. Cell Signal 2010; 22:1597-603. [PMID: 20388539 DOI: 10.1016/j.cellsig.2010.04.003] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2010] [Accepted: 04/02/2010] [Indexed: 12/15/2022]
Abstract
Voltage-gated calcium channels (VGCC) are involved in a large variety of cellular Ca(2+) signaling processes, including exocytosis, a Ca(2+) dependent release of neurotransmitters and hormones. Great progress has been made in understanding the mode of action of VGCC in exocytosis, a process distinguished by two sequential yet independent Ca(2+) binding reactions. First, Ca(2+) binds at the selectivity filter, the EEEE motif of the VGCC, and second, subsequent to a brief and intense Ca(2+) inflow to synaptotagmin, a vesicular protein. Inquiry into the functional and physical interactions of the channels with synaptic proteins has demonstrated that exocytosis is triggered during the initial Ca(2+) binding at the channel pore, prior to Ca(2+) entry. Accordingly, a cycle of secretion begins by an incoming stimulus that releases vesicles from a releasable pool upon Ca(2+) binding at the pore, and at the same time, the transient increase in [Ca(2+)](i) primes a fresh set of non-releasable vesicles, to be fused by the next incoming stimulus. We propose a model, in which the Ca(2+) binding at the EEEE motif and the consequent conformational changes in the channel are the primary event in triggering secretion, while synaptotagmin acts as a vesicle docking protein. Thus, the channel serves as the molecular On/Off signaling switch, where the predominance of a conformational change in Ca(2+)-bound channel provides for the fast secretory process.
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Affiliation(s)
- Daphne Atlas
- Department of Biological Chemistry, The Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem 919104, Israel.
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25
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Marom M, Hagalili Y, Sebag A, Tzvier L, Atlas D. Conformational changes induced in voltage-gated calcium channel Cav1.2 by BayK 8644 or FPL64176 modify the kinetics of secretion independently of Ca2+ influx. J Biol Chem 2010; 285:6996-7005. [PMID: 20054004 DOI: 10.1074/jbc.m109.059865] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The role of the L-type calcium channel (Cav1.2) as a molecular switch that triggers secretion prior to Ca(2+) transport has previously been demonstrated in bovine chromaffin cells and rat pancreatic beta cells. Here, we examined the effect of specific Cav1.2 allosteric modulators, BayK 8644 (BayK) and FPL64176 (FPL), on the kinetics of catecholamine release, as monitored by amperometry in single bovine chromaffin cells. We show that 2 microm BayK or 0.5 microm FPL accelerates the rate of catecholamine secretion to a similar extent in the presence either of the permeable Ca(2+) and Ba(2+) or the impermeable charge carrier La(3+). These results suggest that structural rearrangements generated through the binding of BayK or FPL, by altering the channel activity, could affect depolarization-evoked secretion prior to cation transport. FPL also accelerated the rate of secretion mediated by a Ca(2+)-impermeable channel made by replacing the wild type alpha(1)1.2 subunit was replaced with the mutant alpha(1)1.2/L775P. Furthermore, BayK and FPL modified the kinetic parameters of the fusion pore formation, which represent the initial contact between the vesicle lumen and the extracellular medium. A direct link between the channel activity and evoked secretion lends additional support to the view that the voltage-gated Ca(2+) channels act as a signaling molecular switch, triggering secretion upstream to ion transport into the cell.
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Affiliation(s)
- Merav Marom
- Department of Biological Chemistry, Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem 919104, Israel
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26
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Hagalili Y, Bachnoff N, Atlas D. The Voltage-Gated Ca2+ Channel Is the Ca2+ Sensor Protein of Secretion. Biochemistry 2008; 47:13822-30. [DOI: 10.1021/bi801619f] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Yamit Hagalili
- Department of Biological Chemistry, The Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, 91904 Israel
| | - Niv Bachnoff
- Department of Biological Chemistry, The Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, 91904 Israel
| | - Daphne Atlas
- Department of Biological Chemistry, The Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, 91904 Israel
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27
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Amatore C, Arbault S, Guille M, Lemaître F. Electrochemical Monitoring of Single Cell Secretion: Vesicular Exocytosis and Oxidative Stress. Chem Rev 2008; 108:2585-621. [DOI: 10.1021/cr068062g] [Citation(s) in RCA: 316] [Impact Index Per Article: 19.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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28
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Cohen R, Schmitt BM, Atlas D. Reconstitution of depolarization and Ca2+-evoked secretion in Xenopus oocytes monitored by membrane capacitance. Methods Mol Biol 2008; 440:269-82. [PMID: 18369953 DOI: 10.1007/978-1-59745-178-9_21] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/18/2023]
Abstract
The identity of the proteins that constitute the "minimal molecular machinery" required for depolarization-evoked neurotransmitter release at synapses is still not fully disclosed. Using capacitance monitoring combined with heterologous protein expression in Xenopus oocytes, we were able to reconstitute a fast (<.5 s) secretion that was triggered directly by membrane depolarization. The functional assembly of voltage-gated Ca2+ channel (Cav1.2 or Cav2.2) coexpressed with syntaxin 1A, synaptosome-associated protein of 25 kDa (SNAP-25), and synaptotagmin led to the reconstitution of depolarization-evoked secretion. Botulinum C1, botulinum A, and tetanus toxin were used to establish that this minimal set of proteins, named the excitosome complex, was necessary and sufficient for reconstituting depolarization-induced exocytosis. Similar to synaptic transmission, the capacitance changes were sensitive to neurotoxins, modulated by divalent cations (Ca2+, Ba2+, and Sr2+) or channels (Lc or N type; ionotropic glutamate GLUR3), and depended nonlinearly on extracellular divalent cation concentration. Expression of a recombinant intracellular domain of the calcium channel (Lc753-893) abolished evoked release in the reconstituted assay. Also, mutations at the synaptotagmin C2A polylysine motif, a channel interaction site, abolished depolarization-evoked capacitance transients, consistent with release studies in PC12 cells. Because of its improved speed, native trigger, and great experimental versatility, this reconstitution assay provides a novel, promising tool to study synaptic and nonsynaptic exocytosis and examine the role of other proteins implicated in these processes.
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Affiliation(s)
- Roy Cohen
- Department of Biological Chemistry, The Hebrew University of Jerusalem, Jerusalem, Israel
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29
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Cohen R, Marom M, Atlas D. Depolarization-evoked secretion requires two vicinal transmembrane cysteines of syntaxin 1A. PLoS One 2007; 2:e1273. [PMID: 18060067 PMCID: PMC2094736 DOI: 10.1371/journal.pone.0001273] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2007] [Accepted: 11/14/2007] [Indexed: 11/24/2022] Open
Abstract
Background The interactions of the voltage-gated Ca2+ channel (VGCC) with syntaxin 1A (Sx 1A), Synaptosome-associated protein of 25 kD (SNAP-25), and synaptotagmin, couple electrical excitation to evoked secretion. Two vicinal Cys residues, Cys 271 and Cys 272 in the Sx 1A transmembrane domain, are highly conserved and participate in modulating channel kinetics. Each of the Sx1A Cys mutants, differently modify the kinetics of Cav1.2, and neuronal Cav2.2 calcium channel. Methodology/Principle Findings We examined the effects of various Sx1A Cys mutants and the syntaxin isoforms 2, 3, and 4 each of which lack vicinal Cys residues, on evoked secretion, monitoring capacitance transients in a functional release assay. Membrane capacitance in Xenopus oocytes co-expressing Cav1.2, Sx1A, SNAP-25 and synaptotagmin, which is Bot C- and Bot A-sensitive, was elicited by a double 500 ms depolarizing pulse to 0 mV. The evoked-release was obliterated when a single Cys Sx1A mutant or either one of the Sx isoforms were substituted for Sx 1A, demonstrating the essential role of vicinal Cys residues in the depolarization mediated process. Protein expression and confocal imaging established the level of the mutated proteins in the cell and their targeting to the plasma membrane. Conclusions/Significance We propose a model whereby the two adjacent transmembranal Cys residues of Sx 1A, lash two calcium channels. Consistent with the necessity of a minimal fusion complex termed the excitosome, each Sx1A is in a complex with SNAP-25, Syt1, and the Ca2+ channel. A Hill coefficient >2 imply that at least three excitosome complexes are required for generating a secreting hetero-oligomer protein complex. This working model suggests that a fusion pore that opens during membrane depolarization could be lined by alternating transmembrane segments of Sx1A and VGCC. The functional coupling of distinct amino acids of Sx 1A with VGCC appears to be essential for depolarization-evoked secretion.
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Affiliation(s)
- Roy Cohen
- Department of Biological Chemistry, The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Merav Marom
- Department of Biological Chemistry, The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Daphne Atlas
- Department of Biological Chemistry, The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
- * To whom correspondence should be addressed. E-mail:
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Bruce JIE, Elliott AC. Oxidant-impaired intracellular Ca2+ signaling in pancreatic acinar cells: role of the plasma membrane Ca2+-ATPase. Am J Physiol Cell Physiol 2007; 293:C938-50. [PMID: 17494627 DOI: 10.1152/ajpcell.00582.2006] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Pancreatitis is an inflammatory disease of pancreatic acinar cells whereby intracellular calcium concentration ([Ca(2+)](i)) signaling and enzyme secretion are impaired. Increased oxidative stress has been suggested to mediate the associated cell injury. The present study tested the effects of the oxidant, hydrogen peroxide, on [Ca(2+)](i) signaling in rat pancreatic acinar cells by simultaneously imaging fura-2, to measure [Ca(2+)](i), and dichlorofluorescein, to measure oxidative stress. Millimolar concentrations of hydrogen peroxide increased cellular oxidative stress and irreversibly increased [Ca(2+)](i), which was sensitive to antioxidants and removal of external Ca(2+), and ultimately led to cell lysis. Responses were also abolished by pretreatment with (sarco)endoplasmic reticulum Ca(2+)-ATPase inhibitors, unless cells were prestimulated with cholecystokinin to promote mitochondrial Ca(2+) uptake. This suggests that hydrogen peroxide promotes Ca(2+) release from the endoplasmic reticulum and the mitochondria and that it promotes Ca(2+) influx. Lower concentrations of hydrogen peroxide (10-100 muM) increased [Ca(2+)](i) and altered cholecystokinin-evoked [Ca(2+)](i) oscillations with marked heterogeneity, the severity of which was directly related to oxidative stress, suggesting differences in cellular antioxidant capacity. These changes in [Ca(2+)](i) also upregulated the activity of the plasma membrane Ca(2+)-ATPase in a Ca(2+)-dependent manner, whereas higher concentrations (0.1-1 mM) inactivated the plasma membrane Ca(2+)-ATPase. This may be important in facilitating "Ca(2+) overload," resulting in cell injury associated with pancreatitis.
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Affiliation(s)
- Jason I E Bruce
- Faculty of Life Sciences, 2nd Floor Core Technology Facility, 46 Grafton St., The Univ. of Manchester, Manchester M13 9NT, UK.
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Carabelli V, Marcantoni A, Comunanza V, Carbone E. Fast exocytosis mediated by T- and L-type channels in chromaffin cells: distinct voltage-dependence but similar Ca2+ -dependence. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2007; 36:753-62. [PMID: 17340096 DOI: 10.1007/s00249-007-0138-2] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/24/2006] [Revised: 01/11/2007] [Accepted: 01/27/2007] [Indexed: 12/01/2022]
Abstract
Expression, spatial distribution and specific roles of different Ca(2+) channels in stimulus-secretion coupling of chromaffin cells are intriguing issues still open to discussion. Most of the evidence supports a role of high-voltage activated (HVA) Ca(2+) channels (L-, N-, P/Q- and R-types) in the control of exocytosis: some suggesting a preferential coupling of specific Ca(2+) channel subunits with the secretory apparatus, others favoring the idea of a contribution to secretion proportional to the expression density and gating properties of Ca(2+) channels. In this work we review recent findings and bring new evidence in favor of the hypothesis that also the LVA (low-voltage-activated, T-type) Ca(2+) channels effectively control fast exocytosis near resting potential in adrenal chromaffin cells of adult rats. T-type channels recruited after long-term treatments with pCPT-cAMP (or chronic hypoxia) are shown to control exocytosis with the same efficacy of L-type channels, which are the dominant Ca(2+) channel types expressed in rodent chromaffin cells. A rigorous comparison of T- and L-type channel properties shows that, although operating at different potentials and with different voltage-sensitivity, the two channels possess otherwise similar Ca(2+)-dependence of exocytosis, size and kinetics of depletion of the immediately releasable pool and mobilize vesicles of the same quantal size. Thus, T- and L-type channels are coupled with the same Ca(2+)-efficiency to the secretory apparatus and deplete the same number of vesicles ready for release. The major difference of the secretory signals controlled by the two channels appear to be the voltage range of operation, suggesting the idea that stressful conditions (hypoxia and persistent beta-adrenergic stimulation) can lower the threshold of cell excitability by recruiting new Ca(2+) channels and activate an additional source of catecholamine secretion.
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Affiliation(s)
- V Carabelli
- Department of Neuroscience, Centre of Excellence NIS, CNISM UdR, Corso Raffaello 30, Turin, Italy.
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