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Kühne T, Wallace E, Herzig D, Helleputte S, Scott S, Pickles J, Melmer A, Stettler C. Combined intake of caffeine and low-dose glucose to reduce exercise-related hypoglycaemia in individuals with type 1 diabetes on ultra-long-acting insulin degludec: A randomized, controlled, double-blind, cross-over trial. Diabetes Obes Metab 2024; 26:2645-2651. [PMID: 38558517 DOI: 10.1111/dom.15580] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/26/2023] [Revised: 03/14/2024] [Accepted: 03/16/2024] [Indexed: 04/04/2024]
Abstract
AIM To evaluate whether caffeine combined with a moderate amount of glucose reduces the risk for exercise-related hypoglycaemia compared with glucose alone or control in adult people with type 1 diabetes using ultra-long-acting insulin degludec. MATERIALS AND METHODS Sixteen participants conducted three aerobic exercise sessions (maximum 75 min) in a randomized, double-blind, cross-over design. Thirty minutes before exercise, participants ingested a drink containing either 250 mg of caffeine + 10 g of glucose + aspartame (CAF), 10 g of glucose + aspartame (GLU), or aspartame alone (ASP). The primary outcome was time to hypoglycaemia. RESULTS There was a significant effect of the condition on time to hypoglycaemia (χ2 = 7.674, p = .0216). Pairwise comparisons revealed an 85.7% risk reduction of hypoglycaemia for CAF compared with ASP (p = .044). No difference was observed between GLU and ASP (p = .104) or between CAF and GLU (p = .77). While CAF increased glucose levels during exercise compared with GLU and ASP (8.3 ± 1.9 mmol/L vs. 7.7 ± 2.2 mmol/L vs. 5.8 ± 1.4 mmol/L; p < .001), peak plasma glucose levels during exercise did not differ between CAF and GLU (9.3 ± 1.4 mmol/L and 9.1 ± 1.6 mmol/L, p = .80), but were higher than in ASP (6.6 ± 1.1 mmol/L; p < .001). The difference in glucose levels between CAF and GLU was largest during the last 15 min of exercise (p = .002). Compared with GLU, CAF lowered perceived exertion (p = .023). CONCLUSIONS Pre-exercise caffeine ingestion combined with a low dose of glucose reduced exercise-related hypoglycaemia compared with control while avoiding hyperglycaemia.
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Affiliation(s)
- Tobias Kühne
- Department of Diabetes, Endocrinology, Clinical Nutrition & Metabolism, Inselspital, Bern University Hospital, University of Bern, Bern, Switzerland
| | - Esmè Wallace
- Department of Diabetes, Endocrinology, Clinical Nutrition & Metabolism, Inselspital, Bern University Hospital, University of Bern, Bern, Switzerland
| | - David Herzig
- Department of Diabetes, Endocrinology, Clinical Nutrition & Metabolism, Inselspital, Bern University Hospital, University of Bern, Bern, Switzerland
| | - Simon Helleputte
- Department of Diabetes, Endocrinology, Clinical Nutrition & Metabolism, Inselspital, Bern University Hospital, University of Bern, Bern, Switzerland
| | - Sam Scott
- Department of Diabetes, Endocrinology, Clinical Nutrition & Metabolism, Inselspital, Bern University Hospital, University of Bern, Bern, Switzerland
- Team Novo Nordisk Professional Cycling Team, Atlanta, Georgia, USA
| | - Jordan Pickles
- Department of Diabetes, Endocrinology, Clinical Nutrition & Metabolism, Inselspital, Bern University Hospital, University of Bern, Bern, Switzerland
| | - Andreas Melmer
- Department of Diabetes, Endocrinology, Clinical Nutrition & Metabolism, Inselspital, Bern University Hospital, University of Bern, Bern, Switzerland
| | - Christoph Stettler
- Department of Diabetes, Endocrinology, Clinical Nutrition & Metabolism, Inselspital, Bern University Hospital, University of Bern, Bern, Switzerland
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Zhang Y, Yang W, Xue Y, Hou D, Chen S, Xu Z, Peng S, Zhao H, Wang C, Liu C. Timing Matters: Time of Day Impacts the Ergogenic Effects of Caffeine-A Narrative Review. Nutrients 2024; 16:1421. [PMID: 38794659 PMCID: PMC11124133 DOI: 10.3390/nu16101421] [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: 04/06/2024] [Revised: 05/03/2024] [Accepted: 05/04/2024] [Indexed: 05/26/2024] Open
Abstract
Caffeine has attracted significant attention from researchers in the sports field due to its well-documented ergogenic effects across various athletic disciplines. As research on caffeine continues to progress, there has been a growing emphasis on evaluating caffeine dosage and administration methods. However, investigations into the optimal timing of caffeine intake remain limited. Therefore, this narrative review aimed to assess the ergogenic effects of caffeine administration at different times during the morning (06:00 to 10:00) and evening (16:00 to 21:00). The review findings suggest that circadian rhythms play a substantial role in influencing sports performance, potentially contributing to a decline in morning performance. Caffeine administration has demonstrated effectiveness in mitigating this phenomenon, resulting in ergogenic effects and performance enhancement, even comparable to nighttime levels. While the specific mechanisms by which caffeine regulates circadian rhythms and influences sports performance remain unclear, this review also explores the mechanisms underlying caffeine's ergogenic effects, including the adenosine receptor blockade, increased muscle calcium release, and modulation of catecholamines. Additionally, the narrative review underscores caffeine's indirect impact on circadian rhythms by enhancing responsiveness to light-induced phase shifts. Although the precise mechanisms through which caffeine improves morning performance declines via circadian rhythm regulation necessitate further investigations, it is noteworthy that the timing of caffeine administration significantly affects its ergogenic effects during exercise. This emphasizes the importance of considering caffeine intake timing in future research endeavors to optimize its ergogenic potential and elucidate its mechanisms.
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Affiliation(s)
- Ye Zhang
- Sport Coaching College, Beijing Sport University, Beijing 100084, China
| | - Weijun Yang
- Sport Coaching College, Beijing Sport University, Beijing 100084, China
| | - Yizhang Xue
- Sport Coaching College, Beijing Sport University, Beijing 100084, China
| | - Dingchun Hou
- Institute of Population Research, Peking University, Beijing 100871, China
| | - Songyue Chen
- Department of Bioengineering, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Zhiqin Xu
- School of Sport Science, Beijing Sport University, Beijing 100084, China
| | - Sijia Peng
- National Engineering Research Center of Fruit and Vegetable Processing, College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China
| | - Haotian Zhao
- Department of Physical Education, Jiangnan University, Wuxi 214122, China
| | - Can Wang
- College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China
| | - Chang Liu
- School of Sport Science, Beijing Sport University, Beijing 100084, China
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Ikegawa N, Kozuka A, Morita N, Murakami M, Sasakawa N, Niikura T. Humanin derivative, HNG, enhances neurotransmitter release. Biochim Biophys Acta Gen Subj 2022; 1866:130204. [PMID: 35843407 DOI: 10.1016/j.bbagen.2022.130204] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2022] [Revised: 07/09/2022] [Accepted: 07/12/2022] [Indexed: 11/28/2022]
Abstract
BACKGROUND Humanin (HN) is an endogenous 24-residue peptide that was first identified as a protective factor against neuronal death in Alzheimer's disease (AD). We previously demonstrated that the highly potent HN derivative HNG (HN with substitution of Gly for Ser14) ameliorated cognitive impairment in AD mouse models. Despite the accumulating evidence on the antagonizing effects of HN against cognitive deficits, the mechanisms behind these effects remain to be elucidated. METHODS The extracellular fluid in the hippocampus of wild-type young mice was collected by microdialysis and the amounts of neurotransmitters were measured. The kinetic analysis of exocytosis was performed by amperometry using neuroendocrine cells. RESULTS The hippocampal acetylcholine (ACh) levels were increased by intraperitoneal injection of HNG. HNG did not affect the physical activities of the mice but modestly improved their object memory. In a neuronal cell model, rat pheochromocytoma PC12 cells, HNG enhanced ACh-induced dopamine release. HNG increased ACh-induced secretory events and vesicular quantal size in primary neuroendocrine cells. CONCLUSIONS These findings suggest that HN directly enhances regulated exocytosis in neurons, which can contribute to the improvement of cognitive functions. GENERAL SIGNIFICANCE The regulator of exocytosis is a novel physiological role of HN, which provides a molecular clue for HN's effects on brain functions under health and disease.
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Affiliation(s)
- Natsumi Ikegawa
- Department of Information and Communication Sciences, Faculty of Science and Technology, Sophia University, Japan
| | - Ayari Kozuka
- Department of Information and Communication Sciences, Faculty of Science and Technology, Sophia University, Japan
| | - Nozomi Morita
- Department of Information and Communication Sciences, Faculty of Science and Technology, Sophia University, Japan
| | - Minetaka Murakami
- Department of Information and Communication Sciences, Faculty of Science and Technology, Sophia University, Japan
| | - Nobuyuki Sasakawa
- Department of Information and Communication Sciences, Faculty of Science and Technology, Sophia University, Japan
| | - Takako Niikura
- Department of Information and Communication Sciences, Faculty of Science and Technology, Sophia University, Japan.
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Bergantin LB. The Interactions among Hypertension, Cancer, and COVID-19: Perspectives from Ca2+/cAMP Signalling. Curr Cancer Drug Targets 2022; 22:351-360. [PMID: 35168520 DOI: 10.2174/1568009622666220215143805] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2021] [Revised: 12/02/2021] [Accepted: 12/16/2021] [Indexed: 11/22/2022]
Abstract
BACKGROUND The hypothesis that hypertension is clinically associated with an enhanced risk for developing cancer has been highlighted. However, the working principles involved in this link are still under intensive discussion. A correlation among inflammation, hypertension, and cancer could accurately describe the clinical link between these diseases. In addition, a dyshomeostasis of Ca2+ has been considered as a topic involved in both cancer and hypertension and inflammation. There is a strong link between Ca2+ signalling, e.g. enhanced Ca2+ signals, and inflammatory outcomes. cAMP also modulates pro- and anti-inflammatory outcomes: pharmaceuticals, which increase intracellular cAMP levels, can decrease the production of proinflammatory mediators and enhance the production of anti-inflammatory outcomes. OBJECTIVE This article has discussed the participation of Ca2+/cAMP signalling in the clinical association among inflammation, hypertension, and an enhanced risk for the development of cancer. In addition, considering coronavirus disease 2019 (COVID-19) is a rapidly evolving field, this article also reviews recent reports about the role of Ca2+ channel blockers for restoring Ca2+ signalling disruption due to COVID-19, including the relationship among COVID-19, cancer, and hypertension. CONCLUSION Understanding the association among these diseases could expand current pharmacotherapy, including that involving Ca2+ channel blockers and pharmaceuticals which rise cAMP levels.
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Affiliation(s)
- Leandro Bueno Bergantin
- Department of Pharmacology - Universidade Federal de São Paulo - Escola Paulista de Medicina, Laboratory of Autonomic and Cardiovascular Pharmacology - 55 11 5576-4973, Rua Pedro de Toledo, 669 - Vila Clementino, São Paulo - SP, Brazil
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5
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de Pascual R, Calzaferri F, Gonzalo PC, Serrano-Nieto R, de los Ríos C, García AG, Gandía L. Novel Purine Derivative ITH15004 Facilitates Exocytosis through a Mitochondrial Calcium-Mediated Mechanism. Int J Mol Sci 2021; 23:440. [PMID: 35008868 PMCID: PMC8745631 DOI: 10.3390/ijms23010440] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2021] [Revised: 12/26/2021] [Accepted: 12/29/2021] [Indexed: 02/08/2023] Open
Abstract
Upon depolarization of chromaffin cells (CCs), a prompt release of catecholamines occurs. This event is triggered by a subplasmalemmal high-Ca2+ microdomain (HCMD) generated by Ca2+ entry through nearby voltage-activated calcium channels. HCMD is efficiently cleared by local mitochondria that avidly take up Ca2+ through their uniporter (MICU), then released back to the cytosol through mitochondrial Na+/Ca2+ exchanger (MNCX). We found that newly synthesized derivative ITH15004 facilitated the release of catecholamines triggered from high K+-depolarized bovine CCs. Such effect seemed to be due to regulation of mitochondrial Ca2+ circulation because: (i) FCCP-potentiated secretory responses decay was prevented by ITH15004; (ii) combination of FCCP and ITH15004 exerted additive secretion potentiation; (iii) such additive potentiation was dissipated by the MICU blocker ruthenium red (RR) or the MNCX blocker CGP37157 (CGP); (iv) combination of FCCP and ITH15004 produced both additive augmentation of cytosolic Ca2+ concentrations ([Ca2+]c) K+-challenged BCCs, and (v) non-inactivated [Ca2+]c transient when exposed to RR or CGP. On pharmacological grounds, data suggest that ITH15004 facilitates exocytosis by acting on mitochondria-controlled Ca2+ handling during K+ depolarization. These observations clearly show that ITH15004 is a novel pharmacological tool to study the role of mitochondria in the regulation of the bioenergetics and exocytosis in excitable cells.
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Affiliation(s)
- Ricardo de Pascual
- Instituto Teófilo Hernando and Departamento de Farmacología y Terapéutica, Universidad Autónoma de Madrid, C/Arzobispo Morcillo, 4, 28029 Madrid, Spain; (R.d.P.); (F.C.); (P.C.G.); (R.S.-N.); (C.d.l.R.); (A.G.G.)
- Instituto de Investigación Sanitaria, Hospital Universitario de la Princesa, C/Diego de León, 62, 28006 Madrid, Spain
| | - Francesco Calzaferri
- Instituto Teófilo Hernando and Departamento de Farmacología y Terapéutica, Universidad Autónoma de Madrid, C/Arzobispo Morcillo, 4, 28029 Madrid, Spain; (R.d.P.); (F.C.); (P.C.G.); (R.S.-N.); (C.d.l.R.); (A.G.G.)
- Institut des Biomolécules Max Mousseron (IBMM—UMR5247, CNRS), 1919 Route de Mende, CEDEX 5, 34293 Montpellier, France
| | - Paula C. Gonzalo
- Instituto Teófilo Hernando and Departamento de Farmacología y Terapéutica, Universidad Autónoma de Madrid, C/Arzobispo Morcillo, 4, 28029 Madrid, Spain; (R.d.P.); (F.C.); (P.C.G.); (R.S.-N.); (C.d.l.R.); (A.G.G.)
| | - Rubén Serrano-Nieto
- Instituto Teófilo Hernando and Departamento de Farmacología y Terapéutica, Universidad Autónoma de Madrid, C/Arzobispo Morcillo, 4, 28029 Madrid, Spain; (R.d.P.); (F.C.); (P.C.G.); (R.S.-N.); (C.d.l.R.); (A.G.G.)
| | - Cristóbal de los Ríos
- Instituto Teófilo Hernando and Departamento de Farmacología y Terapéutica, Universidad Autónoma de Madrid, C/Arzobispo Morcillo, 4, 28029 Madrid, Spain; (R.d.P.); (F.C.); (P.C.G.); (R.S.-N.); (C.d.l.R.); (A.G.G.)
- Instituto de Investigación Sanitaria, Hospital Universitario de la Princesa, C/Diego de León, 62, 28006 Madrid, Spain
- Departamento de Ciencias Básicas de la Salud, Campus de Alcorcon, Universidad Rey Juan Carlos, Avda. Atenas s/n, 28922 Alcorcón, Spain
| | - Antonio G. García
- Instituto Teófilo Hernando and Departamento de Farmacología y Terapéutica, Universidad Autónoma de Madrid, C/Arzobispo Morcillo, 4, 28029 Madrid, Spain; (R.d.P.); (F.C.); (P.C.G.); (R.S.-N.); (C.d.l.R.); (A.G.G.)
- Instituto de Investigación Sanitaria, Hospital Universitario de la Princesa, C/Diego de León, 62, 28006 Madrid, Spain
- Fundación Teófilo Hernando, Parque Científico de Madrid, Campus de Cantoblanco, 28049 Madrid, Spain
| | - Luis Gandía
- Instituto Teófilo Hernando and Departamento de Farmacología y Terapéutica, Universidad Autónoma de Madrid, C/Arzobispo Morcillo, 4, 28029 Madrid, Spain; (R.d.P.); (F.C.); (P.C.G.); (R.S.-N.); (C.d.l.R.); (A.G.G.)
- Instituto de Investigación Sanitaria, Hospital Universitario de la Princesa, C/Diego de León, 62, 28006 Madrid, Spain
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Tawfik B, Martins JS, Houy S, Imig C, Pinheiro PS, Wojcik SM, Brose N, Cooper BH, Sørensen JB. Synaptotagmin-7 places dense-core vesicles at the cell membrane to promote Munc13-2- and Ca 2+-dependent priming. eLife 2021; 10:64527. [PMID: 33749593 PMCID: PMC8012061 DOI: 10.7554/elife.64527] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2020] [Accepted: 03/19/2021] [Indexed: 12/17/2022] Open
Abstract
Synaptotagmins confer calcium-dependence to the exocytosis of secretory vesicles, but how coexpressed synaptotagmins interact remains unclear. We find that synaptotagmin-1 and synaptotagmin-7 when present alone act as standalone fast and slow Ca2+-sensors for vesicle fusion in mouse chromaffin cells. When present together, synaptotagmin-1 and synaptotagmin-7 are found in largely non-overlapping clusters on dense-core vesicles. Synaptotagmin-7 stimulates Ca2+-dependent vesicle priming and inhibits depriming, and it promotes ubMunc13-2- and phorbolester-dependent priming, especially at low resting calcium concentrations. The priming effect of synaptotagmin-7 increases the number of vesicles fusing via synaptotagmin-1, while negatively affecting their fusion speed, indicating both synergistic and competitive interactions between synaptotagmins. Synaptotagmin-7 places vesicles in close membrane apposition (<6 nm); without it, vesicles accumulate out of reach of the fusion complex (20-40 nm). We suggest that a synaptotagmin-7-dependent movement toward the membrane is involved in Munc13-2/phorbolester/Ca2+-dependent priming as a prelude to fast and slow exocytosis triggering.
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Affiliation(s)
- Bassam Tawfik
- Department of Neuroscience, University of Copenhagen, Copenhagen, Denmark
| | - Joana S Martins
- Department of Neuroscience, University of Copenhagen, Copenhagen, Denmark
| | - Sébastien Houy
- Department of Neuroscience, University of Copenhagen, Copenhagen, Denmark
| | - Cordelia Imig
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany
| | - Paulo S Pinheiro
- Department of Neuroscience, University of Copenhagen, Copenhagen, Denmark.,Center for Neuroscience and Cell Biology, University of Coimbra, Coimbra, Portugal
| | - Sonja M Wojcik
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany
| | - Nils Brose
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany
| | - Benjamin H Cooper
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany
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7
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Martínez-Ramírez C, Gil-Gómez I, G de Diego AM, García AG. Acute reversible SERCA blockade facilitates or blocks exocytosis, respectively in mouse or bovine chromaffin cells. Pflugers Arch 2021; 473:273-286. [PMID: 33108514 DOI: 10.1007/s00424-020-02483-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2020] [Revised: 10/03/2020] [Accepted: 10/20/2020] [Indexed: 11/29/2022]
Abstract
Pre-blockade of the sarco-endoplasmic reticulum (ER) calcium ATPase (SERCA) with irreversible thapsigargin depresses exocytosis in adrenal bovine chromaffin cells (BCCs). Distinct expression of voltage-dependent Ca2+-channel subtypes and of the Ca2+-induced Ca2+ release (CICR) mechanism in BCCs versus mouse chromaffin cells (MCCs) has been described. We present a parallel study on the effects of the acute SERCA blockade with reversible cyclopizonic acid (CPA), to repeated pulsing with acetylcholine (ACh) at short (15 s) and long intervals (60 s) at 37 °C, allowing the monitoring of the initial size of a ready-release vesicle pool (RRP) and its depletion and recovery in subsequent stimuli. We found (i) strong depression of exocytosis upon ACh pulsing at 15-s intervals and slower depression at 60-s intervals in both cell types; (ii) facilitation of exocytosis upon acute SERCA inhibition, with back to depression upon CPA washout in MCCs; (iii) blockade of exocytosis upon acute SERCA inhibition and pronounced rebound of exocytosis upon CPA washout in BCCs; (iv) basal [Ca2+]c elevation upon stimulation with ACh at short intervals (but not at long intervals) in both cell types; and (v) augmentation of basal [Ca2+]c and inhibition of peak [Ca2+]c amplitude upon CPA treatment in both cell types, with milder effects upon stimulation at 60-s intervals. These results are compatible with the view that while in MCCs the uptake of Ca2+ via SERCA contributes to the mitigation of physiological ACh triggered secretion, in BCCs the uptake of Ca2+ into the ER facilitates such responses likely potentiating a Ca2+-induced Ca2+ release mechanism. These drastic differences in the regulation of ACh-triggered secretion at 37 °C may help to understand different patterns of the regulation of exocytosis by the circulation of Ca2+ at a functional ER Ca2+ store.
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Affiliation(s)
- Carmen Martínez-Ramírez
- Instituto Teófilo Hernando, Universidad Autónoma de Madrid, Madrid, Spain
- Departamento de Farmacología, Universidad Autónoma de Madrid, Madrid, Spain
- Fundación Teófilo Hernando, Parque científico de Madrid, Madrid, Spain
| | - Irene Gil-Gómez
- Instituto Teófilo Hernando, Universidad Autónoma de Madrid, Madrid, Spain
- Departamento de Farmacología, Universidad Autónoma de Madrid, Madrid, Spain
- Fundación Teófilo Hernando, Parque científico de Madrid, Madrid, Spain
| | - Antonio M G de Diego
- Instituto Teófilo Hernando, Universidad Autónoma de Madrid, Madrid, Spain.
- Departamento de Farmacología, Universidad Autónoma de Madrid, Madrid, Spain.
- Fundación Teófilo Hernando, Parque científico de Madrid, Madrid, Spain.
- Instituto de Investigación Sanitaria del Hospital de La Princesa, Facultad de Medicina, Universidad Autónoma de Madrid, Madrid, Spain.
- DNS Neuroscience, Instituto Teófilo Hernando, Department of Pharmacology, Universidad Autónoma de Madrid, Madrid, Spain.
| | - Antonio G García
- Instituto Teófilo Hernando, Universidad Autónoma de Madrid, Madrid, Spain
- Departamento de Farmacología, Universidad Autónoma de Madrid, Madrid, Spain
- Fundación Teófilo Hernando, Parque científico de Madrid, Madrid, Spain
- Instituto de Investigación Sanitaria del Hospital de La Princesa, Facultad de Medicina, Universidad Autónoma de Madrid, Madrid, Spain
- DNS Neuroscience, Instituto Teófilo Hernando, Department of Pharmacology, Universidad Autónoma de Madrid, Madrid, Spain
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8
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Martins GL, Guilherme JPLF, Ferreira LHB, de Souza-Junior TP, Lancha AH. Caffeine and Exercise Performance: Possible Directions for Definitive Findings. Front Sports Act Living 2020; 2:574854. [PMID: 33345139 PMCID: PMC7739593 DOI: 10.3389/fspor.2020.574854] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2020] [Accepted: 11/17/2020] [Indexed: 01/01/2023] Open
Abstract
Caffeine is one of the most studied supplements in the world. Studies correlate its use to increased exercise performance in endurance activities, as well as its possible ergogenic effects for both intermittent and strength activities. Recent findings show that caffeine may increase or decrease exercise performance. These antagonist responses may occur even when using the same dosage and for individuals with the same characteristics, making it challenging to explain caffeine's impact and applicability. This review article provides an analytic look at studies involving the use of caffeine for human physical performance, and addresses factors that could influence the ergogenic effects of caffeine on different proposed activities. These factors subdivide into caffeine effects, daily habits, physiological factors, and genetic factors. Each variable has been focused on by discussions to research related to caffeine. A better understanding and control of these variables should be considered in future research into personalized nutritional strategies.
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Affiliation(s)
- Gabriel Loureiro Martins
- Laboratory of Applied Nutrition and Metabolism, School of Physical Education and Sport, University of São Paulo, São Paulo, Brazil
| | | | - Luis Henrique Boiko Ferreira
- Research Group on Metabolism, Nutrition and Strength Training, Department of Physical Education, Federal University of Parana, Curitiba, Brazil
| | - Tácito Pessoa de Souza-Junior
- Research Group on Metabolism, Nutrition and Strength Training, Department of Physical Education, Federal University of Parana, Curitiba, Brazil
| | - Antonio Herbert Lancha
- Laboratory of Applied Nutrition and Metabolism, School of Physical Education and Sport, University of São Paulo, São Paulo, Brazil
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9
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Direct Observation of Vesicle Transport on the Synaptic Ribbon Provides Evidence That Vesicles Are Mobilized and Prepared Rapidly for Release. J Neurosci 2020; 40:7390-7404. [PMID: 32847965 DOI: 10.1523/jneurosci.0605-20.2020] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2020] [Revised: 07/23/2020] [Accepted: 08/14/2020] [Indexed: 12/12/2022] Open
Abstract
Synaptic ribbons are thought to provide vesicles for continuous release in some retinal nonspiking neurons, yet recent studies indicate that genetic removal of the ribbon has little effect on release kinetics. To investigate vesicle replenishment at synaptic ribbons, we used total internal reflection fluorescence microscopy to image synaptic vesicles and ribbons in retinal bipolar cells of goldfish (Carassius auratus) of both sexes. Analysis of vesicles released by trains of 30 ms depolarizations revealed that most releasable vesicles reside within 300 nm of the ribbon center. A single 30 ms step to 0 mV was sufficient to deplete the membrane-proximal vesicle pool, while triggering rapid stepwise movements of distal vesicles along the ribbon and toward the plasma membrane. Replenishment only becomes rate-limiting for recovery from paired-pulse depression for interstimulus intervals shorter than 250 ms. For longer interstimulus intervals, vesicle movement down the ribbon is fast enough to replenish released vesicles, but newly arrived vesicles are not release-ready. Notably, the rates of vesicle resupply and maturation of newcomers are among the fastest measured optically at any synapse. Lastly, our data show that the delay in vesicle departure increases and vesicle speed decreases with multiple stimuli. Our results support a role for ribbons in the supply of vesicles for release, provide direct measurements of vesicle movement down the ribbon, and suggest that multiple factors contribute to paired-pulse depression.SIGNIFICANCE STATEMENT Synaptic ribbons are macromolecular scaffolds that tether synaptic vesicles close to release sites in nonspiking neurons of the retina and cochlea. Because these neurons release neurotransmitter continuously, synaptic ribbons are assumed to act as platforms for supplying vesicles rapidly in the face of prolonged stimulation. Yet, ribbon synapses suffer from profound paired-pulse depression, which takes seconds to subside. We investigated the mechanistic origin of this phenomenon by directly imaging triggered vesicle movement and release at ribbon sites in retinal bipolar cells, and find that, although ribbon synapses deliver and prime vesicles faster than most conventional synapses, both vesicle absence and vesicle priming contribute to the long recovery from paired-pulse depression.
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10
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Yang L, Fomina AF. Ca 2+ influx and clearance at hyperpolarized membrane potentials modulate spontaneous and stimulated exocytosis in neuroendocrine cells. Cell Calcium 2020; 87:102184. [PMID: 32151786 DOI: 10.1016/j.ceca.2020.102184] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2019] [Revised: 02/10/2020] [Accepted: 02/21/2020] [Indexed: 01/09/2023]
Abstract
Neuroendocrine adrenal chromaffin cells release neurohormones catecholamines in response to Ca2+ entry via voltage-gated Ca2+ channels (VGCCs). Adrenal chromaffin cells also express non-voltage-gated channels, which may conduct Ca2+ at negative membrane potentials, whose role in regulation of exocytosis is poorly understood. We explored how modulation of Ca2+ influx at negative membrane potentials affects basal cytosolic Ca2+ concentration ([Ca2+]i) and exocytosis in metabolically intact voltage-clamped bovine adrenal chromaffin cells. We found that in these cells, Ca2+ entry at negative membrane potentials is balanced by Ca2+ extrusion by the Na+/Ca2+ exchanger and that this balance can be altered by membrane hyperpolarization or stimulation with an inflammatory hormone bradykinin. Membrane hyperpolarization or application of bradykinin augmented Ca2+-carrying current at negative membrane potentials, elevated basal [Ca2+]i, and facilitated synchronous exocytosis evoked by the small amounts of Ca2+ injected into the cell via VGCCs (up to 20 pC). Exocytotic responses evoked by the injections of the larger amounts of Ca2+ via VGCCs (> 20 pC) were suppressed by preceding hyperpolarization. In the absence of Ca2+ entry via VGCCs and Ca2+ extrusion via the Na+/Ca2+ exchanger, membrane hyperpolarization induced a significant elevation in [Ca2+]i and asynchronous exocytosis. Our results indicate that physiological interferences, such as membrane hyperpolarization and/or activation of non-voltage-gated Ca2+ channels, modulate basal [Ca2+]i and, consequently, segregation of exocytotic vesicles and their readiness to be released spontaneously and in response to Ca2+ entry via VGCCs. These mechanisms may play role in homeostatic plasticity of neuronal and endocrine cells.
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Affiliation(s)
- Lukun Yang
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, CA, 95616, USA; Department of Anesthesiology, The 5th Affiliated Hospital of SUN YAT-SEN University, Zhuhai, 519000, China.
| | - Alla F Fomina
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, CA, 95616, USA.
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11
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Carbone E, Borges R, Eiden LE, García AG, Hernández‐Cruz A. Chromaffin Cells of the Adrenal Medulla: Physiology, Pharmacology, and Disease. Compr Physiol 2019; 9:1443-1502. [DOI: 10.1002/cphy.c190003] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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12
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de Pascual R, Álvarez-Ortego N, de Los Ríos C, Jacob-Mazariego G, García AG. Tetrabenazine Facilitates Exocytosis by Enhancing Calcium-Induced Calcium Release through Ryanodine Receptors. J Pharmacol Exp Ther 2019; 371:219-230. [PMID: 31209099 DOI: 10.1124/jpet.119.256560] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2019] [Accepted: 06/04/2019] [Indexed: 11/22/2022] Open
Abstract
Vesicular monoamine transporter-2 is expressed in the presynaptic secretory vesicles membrane in the brain. Its blockade by tetrabenazine (TBZ) causes depletion of dopamine at striatal basal ganglia; this is the mechanism underlying its long-standing use in the treatment of Huntington's disease. In the frame of a project aimed at investigating the kinetics of exocytosis from vesicles with partial emptying of their neurotransmitter, we unexpectedly found that TBZ facilitates exocytosis; thus, we decided to characterize such effect. We used bovine chromaffin cells (BCCs) challenged with repeated pulses of high K+ Upon repeated K+ pulsing, the exocytotic catecholamine release responses were gradually decaying. However, when cells were exposed to TBZ, responses were mildly augmented and decay rate delayed. Facilitation of exocytosis was not due to Ca2+ entry blockade through voltage-activated calcium channels (VACCs) because, in fact, TBZ mildly blocked the whole-cell Ca2+ current. However, TBZ mimicked the facilitatory effects of exocytosis elicited by BayK8644 (L-subtype VACC agonist), an effect blocked by nifedipine (VACC antagonist). On the basis that TBZ augmented the secretory responses to caffeine (but not those of histamine), we monitored its effects on cytosolic Ca2+ elevations ([Ca2+]c) triggered by caffeine or histamine. While the responses to caffeine were augmented twice by TBZ, those of histamine were unaffected; the same happened in rat cortical neurons. Hence, we hypothesize that TBZ facilitates exocytosis by increasing Ca2+ release through the endoplasmic reticulum ryanodine receptor channel (RyR). Confirming this hypothesis are docking results, showing an interaction of TBZ with RyRs. This is consonant with the existence of a healthy Ca2+-induced-Ca2+-release mechanism in BCCs. SIGNIFICANCE STATEMENT: A novel mechanism of action for tetrabenazine (TBZ), a drug used in the therapy of Huntington's disease (HD), is described here. Such mechanism consists of facilitation by combining TBZ with the ryanodine receptor of the endoplasmic reticulum, thereby increasing Ca2+-induced Ca2+ release. This novel mechanism should be taken into account when considering the efficacy and/or safety of TBZ in the treatment of chorea associated with HD and other disorders. Additionally, it could be of interest in the development of novel medicines to treat these pathological conditions.
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Affiliation(s)
- Ricardo de Pascual
- Instituto Teófilo Hernando, Madrid, Spain (R.d.P., N.Á.-O., C.d.l.R., G.J.-M., A.G.G.); and Departamento de Farmacología y Terapéutica (R.d.P., N.Á.-O., G.J.-M., A.G.G.) and Instituto de Investigación Sanitaria, Hospital Universitario de la Princesa (C.d.l.R., A.G.G.), Facultad de Medicina, Universidad Autónoma de Madrid, Madrid, Spain
| | - Nuria Álvarez-Ortego
- Instituto Teófilo Hernando, Madrid, Spain (R.d.P., N.Á.-O., C.d.l.R., G.J.-M., A.G.G.); and Departamento de Farmacología y Terapéutica (R.d.P., N.Á.-O., G.J.-M., A.G.G.) and Instituto de Investigación Sanitaria, Hospital Universitario de la Princesa (C.d.l.R., A.G.G.), Facultad de Medicina, Universidad Autónoma de Madrid, Madrid, Spain
| | - Cristóbal de Los Ríos
- Instituto Teófilo Hernando, Madrid, Spain (R.d.P., N.Á.-O., C.d.l.R., G.J.-M., A.G.G.); and Departamento de Farmacología y Terapéutica (R.d.P., N.Á.-O., G.J.-M., A.G.G.) and Instituto de Investigación Sanitaria, Hospital Universitario de la Princesa (C.d.l.R., A.G.G.), Facultad de Medicina, Universidad Autónoma de Madrid, Madrid, Spain
| | - Gema Jacob-Mazariego
- Instituto Teófilo Hernando, Madrid, Spain (R.d.P., N.Á.-O., C.d.l.R., G.J.-M., A.G.G.); and Departamento de Farmacología y Terapéutica (R.d.P., N.Á.-O., G.J.-M., A.G.G.) and Instituto de Investigación Sanitaria, Hospital Universitario de la Princesa (C.d.l.R., A.G.G.), Facultad de Medicina, Universidad Autónoma de Madrid, Madrid, Spain
| | - Antonio G García
- Instituto Teófilo Hernando, Madrid, Spain (R.d.P., N.Á.-O., C.d.l.R., G.J.-M., A.G.G.); and Departamento de Farmacología y Terapéutica (R.d.P., N.Á.-O., G.J.-M., A.G.G.) and Instituto de Investigación Sanitaria, Hospital Universitario de la Princesa (C.d.l.R., A.G.G.), Facultad de Medicina, Universidad Autónoma de Madrid, Madrid, Spain
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13
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Hydrogen sulphide facilitates exocytosis by regulating the handling of intracellular calcium by chromaffin cells. Pflugers Arch 2018; 470:1255-1270. [DOI: 10.1007/s00424-018-2147-7] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2017] [Revised: 04/10/2018] [Accepted: 04/17/2018] [Indexed: 01/09/2023]
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14
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Houy S, Groffen AJ, Ziomkiewicz I, Verhage M, Pinheiro PS, Sørensen JB. Doc2B acts as a calcium sensor for vesicle priming requiring synaptotagmin-1, Munc13-2 and SNAREs. eLife 2017; 6:27000. [PMID: 29274147 PMCID: PMC5758110 DOI: 10.7554/elife.27000] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2017] [Accepted: 12/21/2017] [Indexed: 01/08/2023] Open
Abstract
Doc2B is a cytosolic protein with binding sites for Munc13 and Tctex-1 (dynein light chain), and two C2-domains that bind to phospholipids, Ca2+ and SNAREs. Whether Doc2B functions as a calcium sensor akin to synaptotagmins, or in other calcium-independent or calcium-dependent capacities is debated. We here show by mutation and overexpression that Doc2B plays distinct roles in two sequential priming steps in mouse adrenal chromaffin cells. Mutating Ca2+-coordinating aspartates in the C2A-domain localizes Doc2B permanently at the plasma membrane, and renders an upstream priming step Ca2+-independent, whereas a separate function in downstream priming depends on SNARE-binding, Ca2+-binding to the C2B-domain of Doc2B, interaction with ubMunc13-2 and the presence of synaptotagmin-1. Another function of Doc2B – inhibition of release during sustained calcium elevations – depends on an overlapping protein domain (the MID-domain), but is separate from its Ca2+-dependent priming function. We conclude that Doc2B acts as a vesicle priming protein.
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Affiliation(s)
- Sébastien Houy
- Neuronal Secretion Group, Department of Neuroscience, University of Copenhagen, København, Denmark
| | - Alexander J Groffen
- Department of Clinical Genetics, Center for Neurogenomics and Cognitive Research, VU Medical Center, Amsterdam, Netherlands
| | - Iwona Ziomkiewicz
- Neuronal Secretion Group, Department of Neuroscience, University of Copenhagen, København, Denmark.,Discovery Sciences, Innovative Medicines and Early Development, AstraZeneca R&D, Cambridge, United Kingdom
| | - Matthijs Verhage
- Department of Clinical Genetics, Center for Neurogenomics and Cognitive Research, VU Medical Center, Amsterdam, Netherlands.,Department of Functional Genomics, Faculty of Science, Center for Neurogenomics and Cognitive Research, VrijeUniversiteit, Amsterdam, Netherlands
| | - Paulo S Pinheiro
- Neuronal Secretion Group, Department of Neuroscience, University of Copenhagen, København, Denmark
| | - Jakob Balslev Sørensen
- Neuronal Secretion Group, Department of Neuroscience, University of Copenhagen, København, Denmark
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15
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The Dual Function of the Polybasic Juxtamembrane Region of Syntaxin 1A in Clamping Spontaneous Release and Stimulating Ca 2+-Triggered Release in Neuroendocrine Cells. J Neurosci 2017; 38:220-231. [PMID: 29133430 DOI: 10.1523/jneurosci.1541-17.2017] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2017] [Revised: 09/07/2017] [Accepted: 10/07/2017] [Indexed: 11/21/2022] Open
Abstract
The exact function of the polybasic juxtamembrane region (5RK) of the plasma membrane neuronal SNARE, syntaxin 1A (Syx), in vesicle exocytosis, although widely studied, is currently not clear. Here, we addressed the role of 5RK in Ca2+-triggered release, using our Syx-based intramolecular fluorescence resonance energy transfer (FRET) probe, which previously allowed us to resolve a depolarization-induced Ca2+-dependent close-to-open transition (CDO) of Syx that occurs concomitant with evoked release, both in PC12 cells and hippocampal neurons and was abolished upon charge neutralization of 5RK. First, using dynamic FRET analysis in PC12 cells, we show that CDO occurs following assembly of SNARE complexes that include the vesicular SNARE, synaptobrevin 2, and that the participation of 5RK in CDO goes beyond its participation in the final zippering of the complex, because mutations of residues adjacent to 5RK, believed to be crucial for final zippering, do not abolish this transition. In addition, we show that CDO is contingent on membrane phosphatidylinositol 4,5-bisphosphate (PIP2), which is fundamental for maintaining regulated exocytosis, as depletion of membranal PIP2 abolishes CDO. Prompted by these results, which underscore a potentially significant role of 5RK in exocytosis, we next amperometrically analyzed catecholamine release from PC12 cells, revealing that charge neutralization of 5RK promotes spontaneous and inhibits Ca2+-triggered release events. Namely, 5RK acts as a fusion clamp, making release dependent on stimulation by Ca2+SIGNIFICANCE STATEMENT Syntaxin 1A (Syx) is a central protein component of the SNARE complex, which underlies neurotransmitter release. Although widely studied in relation to its participation in SNARE complex formation and its interaction with phosphoinositides, the function of Syx's polybasic juxtamembrane region (5RK) remains unclear. Previously, we showed that a conformational transition of Syx, related to calcium-triggered release, reported by a Syx-based FRET probe, is abolished upon charge neutralization of 5RK (5RK/A). Here we show that this conformational transition is dependent on phosphatidylinositol 4,5-bisphosphate (PIP2) and is related to SNARE complex formation. Subsequently, we show that the 5RK/A mutation enhances spontaneous release and inhibits calcium-triggered release in neuroendocrine cells, indicating a previously unrecognized role of 5RK in neurotransmitter release.
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16
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Pulido C, Marty A. Quantal Fluctuations in Central Mammalian Synapses: Functional Role of Vesicular Docking Sites. Physiol Rev 2017; 97:1403-1430. [DOI: 10.1152/physrev.00032.2016] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2016] [Revised: 04/28/2017] [Accepted: 04/29/2017] [Indexed: 12/23/2022] Open
Abstract
Quantal fluctuations are an integral part of synaptic signaling. At the frog neuromuscular junction, Bernard Katz proposed that quantal fluctuations originate at “reactive sites” where specific structures of the presynaptic membrane interact with synaptic vesicles. However, the physical nature of reactive sites has remained unclear, both at the frog neuromuscular junction and at central synapses. Many central synapses, called simple synapses, are small structures containing a single presynaptic active zone and a single postsynaptic density of receptors. Several lines of evidence indicate that simple synapses may release several synaptic vesicles in response to a single action potential. However, in some synapses at least, each release event activates a significant fraction of the postsynaptic receptors, giving rise to a sublinear relation between vesicular release and postsynaptic current. Partial receptor saturation as well as synaptic jitter gives to simple synapse signaling the appearance of a binary process. Recent investigations of simple synapses indicate that the number of released vesicles follows binomial statistics, with a maximum reflecting the number of docking sites present in the active zone. These results suggest that at central synapses, vesicular docking sites represent the reactive sites proposed by Katz. The macromolecular architecture and molecular composition of docking sites are presently investigated with novel combinations of techniques. It is proposed that variations in docking site numbers are central in defining intersynaptic variability and that docking site occupancy is a key parameter regulating short-term synaptic plasticity.
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Affiliation(s)
- Camila Pulido
- Laboratory of Brain Physiology, CNRS UMR 8118, Paris Descartes University, Paris, France
| | - Alain Marty
- Laboratory of Brain Physiology, CNRS UMR 8118, Paris Descartes University, Paris, France
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17
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Datta P, Gilliam J, Thoreson WB, Janz R, Heidelberger R. Two Pools of Vesicles Associated with Synaptic Ribbons Are Molecularly Prepared for Release. Biophys J 2017; 113:2281-2298. [PMID: 28863864 DOI: 10.1016/j.bpj.2017.08.012] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2017] [Revised: 07/28/2017] [Accepted: 08/07/2017] [Indexed: 11/17/2022] Open
Abstract
Neurons that form ribbon-style synapses are specialized for continuous exocytosis. To this end, their synaptic terminals contain numerous synaptic vesicles, some of which are ribbon associated, that have difference susceptibilities for undergoing Ca2+-dependent exocytosis. In this study, we probed the relationship between previously defined vesicle populations and determined their fusion competency with respect to SNARE complex formation. We found that both the rapidly releasing vesicle pool and the releasable vesicle pool of the retinal bipolar cell are situated at the ribbon-style active zones, where they functionally interact. A peptide inhibitor of SNARE complex formation failed to block exocytosis from either pool, suggesting that these two vesicle pools have formed the SNARE complexes necessary for fusion. By contrast, a third, slower component of exocytosis was blocked by the peptide, as was the functional replenishment of vesicle pools, indicating that few vesicles outside of the ribbon-style active zones were initially fusion competent. In cone photoreceptors, similar to bipolar cells, fusion of the initial ribbon-associated synaptic vesicle cohort was not blocked by the SNARE complex-inhibiting peptide, whereas a later phase of exocytosis, attributable to the recruitment and subsequent fusion of vesicles newly arrived at the synaptic ribbons, was blocked. Together, our results support a model in which stimulus-evoked exocytosis in retinal ribbon synapses is SNARE-dependent; where vesicles higher up on the synaptic ribbon replenish the rapidly releasing vesicle pool; and at any given time, there are sufficient SNARE complexes to support the fusion of the entire ribbon-associated cohort of vesicles. An important implication of these results is that ribbon-associated vesicles can form intervesicular SNARE complexes, providing mechanistic insight into compound fusion at ribbon-style synapses.
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Affiliation(s)
- Proleta Datta
- Department of Neurobiology and Anatomy, McGovern Medical School, University of Texas Health Science Center at Houston (UTHealth), Houston, Texas; The University of Texas MD Anderson Cancer Center, UTHealth Graduate School of Biomedical Sciences, Houston, Texas
| | - Jared Gilliam
- Department of Neurobiology and Anatomy, McGovern Medical School, University of Texas Health Science Center at Houston (UTHealth), Houston, Texas
| | - Wallace B Thoreson
- Truhlsen Eye Institute, Department of Ophthalmology and Visual Sciences, University of Nebraska Medical Center, Omaha, Nebraska; Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, Nebraska
| | - Roger Janz
- Department of Neurobiology and Anatomy, McGovern Medical School, University of Texas Health Science Center at Houston (UTHealth), Houston, Texas; The University of Texas MD Anderson Cancer Center, UTHealth Graduate School of Biomedical Sciences, Houston, Texas
| | - Ruth Heidelberger
- Department of Neurobiology and Anatomy, McGovern Medical School, University of Texas Health Science Center at Houston (UTHealth), Houston, Texas; The University of Texas MD Anderson Cancer Center, UTHealth Graduate School of Biomedical Sciences, Houston, Texas.
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18
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Moreira B, Tuoriniemi J, Kouchak Pour N, Mihalčíková L, Safina G. Surface Plasmon Resonance for Measuring Exocytosis from Populations of PC12 Cells: Mechanisms of Signal Formation and Assessment of Analytical Capabilities. Anal Chem 2017; 89:3069-3077. [DOI: 10.1021/acs.analchem.6b04811] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Affiliation(s)
- Beatriz Moreira
- Department
of Chemistry and Molecular Biology, University of Gothenburg, Kemigården
4, 412 96 Gothenburg, Sweden
| | - Jani Tuoriniemi
- Department
of Chemistry and Molecular Biology, University of Gothenburg, Kemigården
4, 412 96 Gothenburg, Sweden
| | - Naghmeh Kouchak Pour
- Department
of Chemistry and Molecular Biology, University of Gothenburg, Kemigården
4, 412 96 Gothenburg, Sweden
| | - Lýdia Mihalčíková
- Department
of Chemistry and Molecular Biology, University of Gothenburg, Kemigården
4, 412 96 Gothenburg, Sweden
| | - Gulnara Safina
- Department
of Chemistry and Molecular Biology, University of Gothenburg, Kemigården
4, 412 96 Gothenburg, Sweden
- Division
of Biological Physics, Department of Physics, Chalmers University of Technology, Kemigården 1, 412 96 Gothenburg, Sweden
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19
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López-Gil A, Nanclares C, Méndez-López I, Martínez-Ramírez C, de Los Rios C, Padín-Nogueira JF, Montero M, Gandía L, García AG. The quantal catecholamine release from mouse chromaffin cells challenged with repeated ACh pulses is regulated by the mitochondrial Na + /Ca 2+ exchanger. J Physiol 2017; 595:2129-2146. [PMID: 27982456 DOI: 10.1113/jp273339] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2016] [Accepted: 11/30/2016] [Indexed: 01/09/2023] Open
Abstract
KEY POINTS Upon repeated application of short ACh pulses to C57BL6J mouse chromaffin cells, the amperometrically monitored secretory responses promptly decayed to a steady-state level of around 25% of the initial response. A subsequent K+ pulse, however, overcame such decay. These data suggest that mouse chromaffin cells have a ready release-vesicle pool that is selectively recruited by the physiological neurotransmitter ACh. The ACh-sensitive vesicle pool is refilled and maintained by the rate of Ca2+ delivery from mitochondria to the cytosol, through the mitochondrial Na+ /Ca2+ exchanger (mNCX). ITH12662, a novel blocker of the mNCX, prevented the decay of secretion elicited by ACh pulses and delayed the rate of [Ca2+ ]c clearance. This regulatory pathway may be physiologically relevant in situations of prolonged stressful conflicts where a sustained catecholamine release is regulated by mitochondrial Ca2+ circulation through the mNCX, which couples respiration and ATP synthesis to long-term stimulation of chromaffin cells by endogenously released ACh. ABSTRACT Using caged-Ca2+ photorelease or paired depolarising pulses in voltage-clamped chromaffin cells (CCs), various pools of secretory vesicles with different readiness to undergo exocytosis have been identified. Whether these pools are present in unclamped CCs challenged with ACh, the physiological neurotransmitter at the splanchnic nerve-CC synapse, is unknown. We have explored here whether an ACh-sensitive ready-release vesicle pool (ASP) is present in C57BL6J mouse chromaffin cells (MCCs). Single cells were fast perfused with a Tyrode solution at 37°C, and challenged with 12 sequential ACh pulses (100 μm, 2 s, every 30 s) plus a K+ pulse given at the end (75 mm K+ ). After the first 2-3 ACh pulses the amperometrically monitored secretory responses promptly decayed to a steady-state level of around 25% of the initial response. The last K+ pulse, however, overcame such decay. Repeated ACh pulses to voltage-clamped cells elicited non-desensitising nicotinic currents. Also, the [Ca2+ ]c transients elicited by repeated ACh pulses that were superimposed on a stable baseline elevation did not undergo decay. The novel blocker of the mitochondrial Na+ /Ca2+ exchanger (mNCX) ITH12662 prevented the decay of secretion elicited by ACh pulses and delayed the rate of [Ca2+ ]c clearance. The experiments are compatible with the idea that C57BL6J MCCs have an ASP vesicle pool that is selectively recruited by the physiological neurotransmitter ACh and is regulated by the rate of Ca2+ delivery from mitochondria to the cytosol, through the mNCX.
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Affiliation(s)
- Angela López-Gil
- Instituto Teófilo Hernando, Universidad Autónoma de Madrid, C/ Arzobispo Morcillo, 4, 28029, Madrid, Spain
| | - Carmen Nanclares
- Instituto Teófilo Hernando, Universidad Autónoma de Madrid, C/ Arzobispo Morcillo, 4, 28029, Madrid, Spain.,Departamento de Farmacología y Terapéutica, Facultad de Medicina, Universidad Autónoma de Madrid, C/ Arzobispo Morcillo, 4, 28029, Madrid, Spain
| | - Iago Méndez-López
- Instituto Teófilo Hernando, Universidad Autónoma de Madrid, C/ Arzobispo Morcillo, 4, 28029, Madrid, Spain.,Departamento de Farmacología y Terapéutica, Facultad de Medicina, Universidad Autónoma de Madrid, C/ Arzobispo Morcillo, 4, 28029, Madrid, Spain
| | - Carmen Martínez-Ramírez
- Instituto Teófilo Hernando, Universidad Autónoma de Madrid, C/ Arzobispo Morcillo, 4, 28029, Madrid, Spain.,Departamento de Farmacología y Terapéutica, Facultad de Medicina, Universidad Autónoma de Madrid, C/ Arzobispo Morcillo, 4, 28029, Madrid, Spain
| | - Cristóbal de Los Rios
- Instituto Teófilo Hernando, Universidad Autónoma de Madrid, C/ Arzobispo Morcillo, 4, 28029, Madrid, Spain.,Instituto de Investigación Sanitaria, Hospital Universitario de la Princesa, Universidad Autónoma de Madrid, c/ Diego de León, 62, 28006, Madrid, Spain
| | - J Fernando Padín-Nogueira
- Instituto Teófilo Hernando, Universidad Autónoma de Madrid, C/ Arzobispo Morcillo, 4, 28029, Madrid, Spain.,Departamento de Farmacología y Terapéutica, Facultad de Medicina, Universidad Autónoma de Madrid, C/ Arzobispo Morcillo, 4, 28029, Madrid, Spain
| | - Mayte Montero
- Instituto de Biologia y Genética Molecular, Universidad de Valladolid, c/ Sanz y Forés, 3, 47003, Valladolid, Spain
| | - Luis Gandía
- Instituto Teófilo Hernando, Universidad Autónoma de Madrid, C/ Arzobispo Morcillo, 4, 28029, Madrid, Spain.,Departamento de Farmacología y Terapéutica, Facultad de Medicina, Universidad Autónoma de Madrid, C/ Arzobispo Morcillo, 4, 28029, Madrid, Spain
| | - Antonio G García
- Instituto Teófilo Hernando, Universidad Autónoma de Madrid, C/ Arzobispo Morcillo, 4, 28029, Madrid, Spain.,Departamento de Farmacología y Terapéutica, Facultad de Medicina, Universidad Autónoma de Madrid, C/ Arzobispo Morcillo, 4, 28029, Madrid, Spain.,Instituto de Investigación Sanitaria, Hospital Universitario de la Princesa, Universidad Autónoma de Madrid, c/ Diego de León, 62, 28006, Madrid, Spain
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20
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Pinheiro PS, Houy S, Sørensen JB. C2-domain containing calcium sensors in neuroendocrine secretion. J Neurochem 2016; 139:943-958. [DOI: 10.1111/jnc.13865] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2016] [Revised: 09/17/2016] [Accepted: 10/05/2016] [Indexed: 12/11/2022]
Affiliation(s)
- Paulo S. Pinheiro
- Center for Neuroscience and Cell Biology; University of Coimbra; Coimbra Portugal
| | - Sébastien Houy
- Department of Neuroscience and Pharmacology; Faculty of Health and Medical Sciences; University of Copenhagen; Copenhagen Denmark
| | - Jakob B. Sørensen
- Department of Neuroscience and Pharmacology; Faculty of Health and Medical Sciences; University of Copenhagen; Copenhagen Denmark
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21
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Regulation by L channels of Ca(2+)-evoked secretory responses in ouabain-treated chromaffin cells. Pflugers Arch 2016; 468:1779-92. [PMID: 27558258 DOI: 10.1007/s00424-016-1866-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2016] [Revised: 07/21/2016] [Accepted: 08/08/2016] [Indexed: 10/21/2022]
Abstract
It is known that the sustained depolarisation of adrenal medullary bovine chromaffin cells (BCCs) with high K(+) concentrations produces an initial sharp catecholamine release that subsequently fades off in spite depolarisation persists. Here, we have recreated a sustained depolarisation condition of BCCs by treating them with the Na(+)/K(+) ATPase blocker ouabain; in doing so, we searched experimental conditions that permitted the development of a sustained long-term catecholamine release response that could be relevant during prolonged stress. BCCs were perifused with nominal 0Ca(2+) solution, and secretion responses were elicited by intermittent application of short 2Ca(2+) pulses (Krebs-HEPES containing 2 mM Ca(2+)). These pulses elicited a biphasic secretory pattern with an initial 30-min period with secretory responses of increasing amplitude and a second 30-min period with steady-state, non-inactivating responses. The initial phase was not due to gradual depolarisation neither to gradual increases of the cytosolic calcium transients ([Ca(2+)]c) elicited by 2Ca(2+) pulses in BBCs exposed to ouabain; both parameters increased soon after ouabain addition. Νifedipine blocked these responses, and FPL64176 potentiated them, suggesting that they were triggered by Ca(2+) entry through non-inactivating L-type calcium channels. This was corroborated by nifedipine-evoked blockade of the L-type Ca(2+) channel current and the [Ca(2+)]c transients elicited by 2Ca(2+) pulses. Furthermore, the plasmalemmal Na(+)/Ca(2+) exchanger (NCX) blocker SEA0400 caused a mild inhibition followed by a large rebound increase of the steady-state secretory responses. We conclude that these two phases of secretion are mostly contributed by Ca(2+) entry through L calcium channels, with a minor contribution of Ca(2+) entry through the reverse mode of the NCX.
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Moya-Díaz J, Álvarez YD, Montenegro M, Bayonés L, Belingheri AV, González-Jamett AM, Cárdenas AM, Marengo FD. Sustained Exocytosis after Action Potential-Like Stimulation at Low Frequencies in Mouse Chromaffin Cells Depends on a Dynamin-Dependent Fast Endocytotic Process. Front Cell Neurosci 2016; 10:184. [PMID: 27507935 PMCID: PMC4960491 DOI: 10.3389/fncel.2016.00184] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2016] [Accepted: 07/08/2016] [Indexed: 12/17/2022] Open
Abstract
Under basal conditions the action potential firing rate of adrenal chromaffin cells is lower than 0.5 Hz. The maintenance of the secretory response at such frequencies requires a continuous replenishment of releasable vesicles. However, the mechanism that allows such vesicle replenishment remains unclear. Here, using membrane capacitance measurements on mouse chromaffin cells, we studied the mechanism of replenishment of a group of vesicles released by a single action potential-like stimulus (APls). The exocytosis triggered by APls (ETAP) represents a fraction (40%) of the immediately releasable pool, a group of vesicles highly coupled to voltage dependent calcium channels. ETAP was replenished with a time constant of 0.73 ± 0.11 s, fast enough to maintain synchronous exocytosis at 0.2–0.5 Hz stimulation. Regarding the mechanism involved in rapid ETAP replenishment, we found that it depends on the ready releasable pool; indeed depletion of this vesicle pool significantly delays ETAP replenishment. On the other hand, ETAP replenishment also correlates with a dynamin-dependent fast endocytosis process (τ = 0.53 ± 0.01 s). In this regard, disruption of dynamin function markedly inhibits the fast endocytosis and delays ETAP replenishment, but also significantly decreases the synchronous exocytosis during repetitive APls stimulation at low frequencies (0.2 and 0.5 Hz). Considering these findings, we propose a model in where both the transfer of vesicles from ready releasable pool and fast endocytosis allow rapid ETAP replenishment during low stimulation frequencies.
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Affiliation(s)
- José Moya-Díaz
- Departamento de Fisiología y Biología Molecular y Celular, Facultad de Ciencias Exactas y Naturales, Instituto de Fisiología, Biología Molecular y Neurociencias, Universidad de Buenos Aires, Consejo Nacional de Investigaciones Científicas y Técnicas Buenos Aires, Argentina
| | - Yanina D Álvarez
- Departamento de Fisiología y Biología Molecular y Celular, Facultad de Ciencias Exactas y Naturales, Instituto de Fisiología, Biología Molecular y Neurociencias, Universidad de Buenos Aires, Consejo Nacional de Investigaciones Científicas y Técnicas Buenos Aires, Argentina
| | - Mauricio Montenegro
- Departamento de Fisiología y Biología Molecular y Celular, Facultad de Ciencias Exactas y Naturales, Instituto de Fisiología, Biología Molecular y Neurociencias, Universidad de Buenos Aires, Consejo Nacional de Investigaciones Científicas y Técnicas Buenos Aires, Argentina
| | - Lucas Bayonés
- Departamento de Fisiología y Biología Molecular y Celular, Facultad de Ciencias Exactas y Naturales, Instituto de Fisiología, Biología Molecular y Neurociencias, Universidad de Buenos Aires, Consejo Nacional de Investigaciones Científicas y Técnicas Buenos Aires, Argentina
| | - Ana V Belingheri
- Departamento de Fisiología y Biología Molecular y Celular, Facultad de Ciencias Exactas y Naturales, Instituto de Fisiología, Biología Molecular y Neurociencias, Universidad de Buenos Aires, Consejo Nacional de Investigaciones Científicas y Técnicas Buenos Aires, Argentina
| | - Arlek M González-Jamett
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso Valparaíso, Chile
| | - Ana M Cárdenas
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso Valparaíso, Chile
| | - Fernando D Marengo
- Departamento de Fisiología y Biología Molecular y Celular, Facultad de Ciencias Exactas y Naturales, Instituto de Fisiología, Biología Molecular y Neurociencias, Universidad de Buenos Aires, Consejo Nacional de Investigaciones Científicas y Técnicas Buenos Aires, Argentina
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23
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Abstract
Exocytosis is the fundamental process by which cells communicate with each other. The events that lead up to the fusion of a vesicle loaded with chemical messenger with the cell membrane were the subject of a Nobel Prize in 2013. However, the processes occurring after the initial formation of a fusion pore are very much still in debate. The release of chemical messenger has traditionally been thought to occur through full distention of the vesicle membrane, hence assuming exocytosis to be all or none. In contrast to the all or none hypothesis, here we discuss the evidence that during exocytosis the vesicle-membrane pore opens to release only a portion of the transmitter content during exocytosis and then close again. This open and closed exocytosis is distinct from kiss-and-run exocytosis, in that it appears to be the main content released during regular exocytosis. The evidence for this partial release via open and closed exocytosis is presented considering primarily the quantitative evidence obtained with amperometry.
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Abstract
This review compares the biological and physiological function of Sigma receptors [σRs] and their potential therapeutic roles. Sigma receptors are widespread in the central nervous system and across multiple peripheral tissues. σRs consist of sigma receptor one (σ1R) and sigma receptor two (σ2R) and are expressed in numerous regions of the brain. The sigma receptor was originally proposed as a subtype of opioid receptors and was suggested to contribute to the delusions and psychoses induced by benzomorphans such as SKF-10047 and pentazocine. Later studies confirmed that σRs are non-opioid receptors (not an µ opioid receptor) and play a more diverse role in intracellular signaling, apoptosis and metabolic regulation. σ1Rs are intracellular receptors acting as chaperone proteins that modulate Ca2+ signaling through the IP3 receptor. They dynamically translocate inside cells, hence are transmembrane proteins. The σ1R receptor, at the mitochondrial-associated endoplasmic reticulum membrane, is responsible for mitochondrial metabolic regulation and promotes mitochondrial energy depletion and apoptosis. Studies have demonstrated that they play a role as a modulator of ion channels (K+ channels; N-methyl-d-aspartate receptors [NMDAR]; inositol 1,3,5 triphosphate receptors) and regulate lipid transport and metabolism, neuritogenesis, cellular differentiation and myelination in the brain. σ1R modulation of Ca2+ release, modulation of cardiac myocyte contractility and may have links to G-proteins. It has been proposed that σ1Rs are intracellular signal transduction amplifiers. This review of the literature examines the mechanism of action of the σRs, their interaction with neurotransmitters, pharmacology, location and adverse effects mediated through them.
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Affiliation(s)
- Colin G Rousseaux
- a Department of Pathology and Laboratory Medicine , University of Ottawa , Ottawa , ON , Canada and
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25
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Dou H, Wang C, Wu X, Yao L, Zhang X, Teng S, Xu H, Liu B, Wu Q, Zhang Q, Hu M, Wang Y, Wang L, Wu Y, Shang S, Kang X, Zheng L, Zhang J, Raoux M, Lang J, Li Q, Su J, Yu X, Chen L, Zhou Z. Calcium influx activates adenylyl cyclase 8 for sustained insulin secretion in rat pancreatic beta cells. Diabetologia 2015; 58:324-33. [PMID: 25381556 DOI: 10.1007/s00125-014-3437-z] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/16/2014] [Accepted: 10/08/2014] [Indexed: 01/07/2023]
Abstract
AIMS/HYPOTHESIS Insulin is a key metabolic regulator in health and diabetes. In pancreatic beta cells, insulin release is regulated by the major second messengers Ca(2+) and cAMP: exocytosis is triggered by Ca(2+) and mediated by the cAMP/protein kinase A (PKA) signalling pathway. However, the causal link between these two processes in primary beta cells remains undefined. METHODS Time-resolved confocal imaging of fluorescence resonance energy transfer signals was performed to visualise PKA activity, and combined membrane capacitance recordings were used to monitor insulin secretion from patch-clamped rat beta cells. RESULTS Membrane depolarisation-induced Ca(2+) influx caused an increase in cytosolic PKA activity via activating a Ca(2+)-sensitive adenylyl cyclase 8 (ADCY8) subpool. Glucose stimulation triggered coupled Ca(2+) oscillations and PKA activation. ADCY8 knockdown significantly reduced the level of depolarisation-evoked PKA activation and impaired replenishment of the readily releasable vesicle pool. Pharmacological inhibition of PKA by two inhibitors reduced depolarisation-induced PKA activation to a similar extent and reduced the capacity for sustained vesicle exocytosis and insulin release. CONCLUSIONS/INTERPRETATION Our findings suggest that depolarisation-induced Ca(2+) influx plays dual roles in regulating exocytosis in rat pancreatic beta cells by triggering vesicle fusion and replenishing the vesicle pool to support sustained insulin release. Therefore, Ca(2+) influx may be important for glucose-stimulated insulin secretion.
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Affiliation(s)
- Haiqiang Dou
- Institute of Molecular Medicine, Peking University, 5 Yiheyuan Road, Beijing, 100871, China
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Fernández-Morales JC, Padín JF, Arranz-Tagarro JA, Vestring S, García AG, de Diego AMG. Hypoxia-elicited catecholamine release is controlled by L-type as well as N/PQ types of calcium channels in rat embryo chromaffin cells. Am J Physiol Cell Physiol 2014; 307:C455-65. [PMID: 24990647 DOI: 10.1152/ajpcell.00101.2014] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
At early life, the adrenal chromaffin cells respond with a catecholamine surge under hypoxic conditions. This response depends on Ca(2+) entry through voltage-activated calcium channels (VACCs). We have investigated here three unresolved questions that concern this response in rat embryo chromaffin cells (ECCs): 1) the relative contribution of L (α1D, Cav1.3), N (α1B, Cav2.2), and PQ (α1A, Cav2.1) to the whole cell Ca(2+) current (ICa); 2) the relative contribution of L and N/PQ channels to the cytosolic Ca(2+) elevations triggered by hypoxia (Δ[Ca(2+)]c); and 3) the role of L and non-L high-VACCs in the regulation of the catecholamine surge occurring during prolonged (1 min) hypoxia exposure of ECCs. Nimodipine halved peak ICa and blocked 60% the total Ca(2+) entry during a 50-ms depolarizing pulse to 0 mV (QCa). Combined ω-agatoxin IVA plus ω-conotoxin GVIA (Aga/GVIA) blocked 30% of both ICa peak and QCa. This relative proportion of L- and non-L VACCs was corroborated by Western blot that indicated 55, 23, and 25% relative expression of L, N, and PQ VACCs. Exposure of ECCs to hypoxia elicited a mild but sustained Δ[Ca(2+)]c; the area of Δ[Ca(2+)]c was blocked 50% by nifedipine and 10% by Aga/GVIA. Exposure of ECCs to 1-min hypoxia elicited an initial transient burst of amperometric secretory spikes followed by scattered spikes along the time of cell exposure to hypoxia. This bulk response was blocked 85% by nimodipine and 35% by Aga/GVIA. Histograms on secretory spike frequency vs. time indicated a faster initial inactivation when Ca(2+) entry took place through N/PQ channels; more sustained secretion but at a lower rate was associated to Ca(2+) entry through L channels. The results suggest that the HIS response may initially be controlled by L and P/Q channels, but later on, N/PQ channels inactivate and the delayed HIS response is maintained at lower rate by slow-inactivating L channels.
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Affiliation(s)
- José-Carlos Fernández-Morales
- Instituto Teófilo Hernando, Facultad de Medicina, Universidad Autónoma de Madrid, Madrid, Spain; Departamento de Farmacología y Terapéutica, Facultad de Medicina, Universidad Autónoma de Madrid, Madrid, Spain
| | - Juan-Fernando Padín
- Instituto Teófilo Hernando, Facultad de Medicina, Universidad Autónoma de Madrid, Madrid, Spain; Departamento de Farmacología y Terapéutica, Facultad de Medicina, Universidad Autónoma de Madrid, Madrid, Spain
| | - Juan-Alberto Arranz-Tagarro
- Instituto Teófilo Hernando, Facultad de Medicina, Universidad Autónoma de Madrid, Madrid, Spain; Departamento de Farmacología y Terapéutica, Facultad de Medicina, Universidad Autónoma de Madrid, Madrid, Spain
| | - Stefan Vestring
- Medizinische Fakultät Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany
| | - Antonio G García
- Instituto Teófilo Hernando, Facultad de Medicina, Universidad Autónoma de Madrid, Madrid, Spain; Departamento de Farmacología y Terapéutica, Facultad de Medicina, Universidad Autónoma de Madrid, Madrid, Spain; Servicio de Farmacología Clínica, Instituto de Investigación Sanitaria, Hospital Universitario de la Princesa, Universidad Autónoma de Madrid, Madrid, Spain; and
| | - Antonio Miguel G de Diego
- Instituto Teófilo Hernando, Facultad de Medicina, Universidad Autónoma de Madrid, Madrid, Spain; Departamento de Farmacología y Terapéutica, Facultad de Medicina, Universidad Autónoma de Madrid, Madrid, Spain;
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Castellano-Muñoz M, Ricci AJ. Role of intracellular calcium stores in hair-cell ribbon synapse. Front Cell Neurosci 2014; 8:162. [PMID: 24971053 PMCID: PMC4054790 DOI: 10.3389/fncel.2014.00162] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2014] [Accepted: 05/28/2014] [Indexed: 11/13/2022] Open
Abstract
Intracellular calcium stores control many neuronal functions such as excitability, gene expression, synaptic plasticity, and synaptic release. Although the existence of calcium stores along with calcium-induced calcium release (CICR) has been demonstrated in conventional and ribbon synapses, functional significance and the cellular mechanisms underlying this role remains unclear. This review summarizes recent experimental evidence identifying contribution of CICR to synaptic transmission and synaptic plasticity in the CNS, retina and inner ear. In addition, the potential role of CICR in the recruitment of vesicles to releasable pools in hair-cell ribbon synapses will be specifically discussed.
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Affiliation(s)
| | - Anthony J Ricci
- Department of Otolaryngology, Stanford University School of Medicine Stanford, CA, USA ; Department of Molecular and Cellular Physiology, Stanford University School of Medicine Stanford, CA, USA
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28
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Abstract
Large dense core vesicle (LDCV) exocytosis in chromaffin cells follows a well characterized process consisting of docking, priming, and fusion. Total internal reflection fluorescence microscopy (TIRFM) studies suggest that some LDCVs, although being able to dock, are resistant to calcium-triggered release. This phenomenon termed dead-end docking has not been investigated until now. We characterized dead-end vesicles using a combination of membrane capacitance measurement and visualization of LDCVs with TIRFM. Stimulation of bovine chromaffin cells for 5 min with 6 μm free intracellular Ca2+ induced strong secretion and a large reduction of the LDCV density at the plasma membrane. Approximately 15% of the LDCVs were visible at the plasma membrane throughout experiments, indicating they were permanently docked dead-end vesicles. Overexpression of Munc18-2 or SNAP-25 reduced the fraction of dead-end vesicles. Conversely, expressing open-syntaxin increased the fraction of dead-end vesicles. These results indicate the existence of the unproductive target soluble N-ethylmaleimide-sensitive factor attachment protein receptor acceptor complex composed of 2:1 syntaxin-SNAP-25 in vivo. More importantly, they define a novel function for this acceptor complex in mediating dead-end docking.
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29
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Caricati-Neto A, Padín JF, Silva-Junior ED, Fernández-Morales JC, de Diego AMG, Jurkiewicz A, García AG. Novel features on the regulation by mitochondria of calcium and secretion transients in chromaffin cells challenged with acetylcholine at 37°C. Physiol Rep 2013; 1:e00182. [PMID: 24744861 PMCID: PMC3970745 DOI: 10.1002/phy2.182] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2013] [Accepted: 11/01/2013] [Indexed: 01/14/2023] Open
Abstract
From experiments performed at room temperature, we know that the buffering of Ca2+ by mitochondria contributes to the shaping of the bulk cytosolic calcium transient ([Ca2+]c) and secretion transients of chromaffin cells stimulated with depolarizing pulses. We also know that the mitochondrial Ca2+ transporters and the release of catecholamine are faster at 37°C with respect to room temperature. Therefore, we planned this investigation to gain further insight into the contribution of mitochondrial Ca2+ buffering to the shaping of [Ca2+]c and catecholamine release transients, using some novel experimental conditions that have not been yet explored namely: (1) perifusion of bovine chromaffin cells (BCCs) with saline at 37°C and their repeated challenging with the physiological neurotransmitter acetylcholine (ACh); (2) separate blockade of mitochondrial Ca2+ uniporter (mCUP) with Ru360 or the mitochondrial Na+/Ca2+ exchanger (mNCX) with CGP37157; (3) full blockade of the mitochondrial Ca2+ cycling (mCC) by the simultaneous inhibition of the mCUP and the mNCX. Ru360 caused a pronounced delay of [Ca2+]c clearance and augmented secretion. In contrast, CGP37157 only caused a tiny delay of [Ca2+]c clearance and a mild decrease in secretion. The mCC resulting in continued Ca2+ uptake and its release back into the cytosol was interrupted by combined Ru360 + CGP37157 (Ru/CGP), the protonophore carbonyl cyanide‐p‐trifluoromethoxyphenylhydrazone, or combined oligomycin + rotenone (O/R); these three treatments caused a mild but sustained elevation of basal [Ca2+]c that, however, was not accompanied by a parallel increase in basal secretion. Nevertheless, all treatments caused a pronounced augmentation of ACh‐induced secretion, with minor changes of the ACh‐induced [Ca2+]c transients. Combined Ru/CGP did not alter the resting membrane potential in current‐clamped cells. Additionally, Ru/CGP did not increase basal [Ca2+]c near subplasmalemmal sites and caused a mild decrease in the size of the readily releasable vesicle pool. Our results provide new functional features in support of the view that in BCCs there are two subpopulations of mitochondria, M1 underneath the plasmalemma nearby exocytotic sites and M2 at the core cell nearby vesicle transport sites. While M1 serves to shape the ACh‐elicited exocytotic response through its efficient Ca2+ removal by the mCUP, M2 shapes the lower [Ca2+]c elevations required for new vesicle supply to the exocytotic machinery, from the large reserve vesicle pool at the cell core. The mCUP of the M1 pool seems to play a more prominent role in controlling the ACh responses, in comparison with the mNCX. Regulation by mitochondria of exocytosis at 37°C.
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Affiliation(s)
- Afonso Caricati-Neto
- Departamento de Farmacología, Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, Brazil
| | - Juan-Fernando Padín
- Instituto Teófilo Hernando, Facultad de Medicina, Universidad Autónoma de Madrid, C/Arzobispo Morcillo, 4, Madrid, 28029, Spain ; Departamento de Farmacología y Terapéutica, Facultad de Medicina, Universidad Autónoma de Madrid, C/Arzobispo Morcillo, 4, 28029Madrid, Spain
| | - Edilson-Dantas Silva-Junior
- Departamento de Farmacología, Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, Brazil
| | - José-Carlos Fernández-Morales
- Instituto Teófilo Hernando, Facultad de Medicina, Universidad Autónoma de Madrid, C/Arzobispo Morcillo, 4, Madrid, 28029, Spain ; Departamento de Farmacología y Terapéutica, Facultad de Medicina, Universidad Autónoma de Madrid, C/Arzobispo Morcillo, 4, 28029Madrid, Spain
| | - Antonio-Miguel G de Diego
- Instituto Teófilo Hernando, Facultad de Medicina, Universidad Autónoma de Madrid, C/Arzobispo Morcillo, 4, Madrid, 28029, Spain ; Departamento de Farmacología y Terapéutica, Facultad de Medicina, Universidad Autónoma de Madrid, C/Arzobispo Morcillo, 4, 28029Madrid, Spain
| | - Aron Jurkiewicz
- Departamento de Farmacología, Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, Brazil
| | - Antonio G García
- Instituto Teófilo Hernando, Facultad de Medicina, Universidad Autónoma de Madrid, C/Arzobispo Morcillo, 4, Madrid, 28029, Spain ; Departamento de Farmacología y Terapéutica, Facultad de Medicina, Universidad Autónoma de Madrid, C/Arzobispo Morcillo, 4, 28029Madrid, Spain ; Servicio de Farmacología Clínica, Instituto de Investigación Sanitaria, Hospital Universitario de la Princesa, Universidad Autónoma de Madrid, C/Diego de León, 62, Madrid, 28006, Spain
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Doc2b synchronizes secretion from chromaffin cells by stimulating fast and inhibiting sustained release. J Neurosci 2013; 33:16459-70. [PMID: 24133251 DOI: 10.1523/jneurosci.2656-13.2013] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Synaptotagmin-1 and -7 constitute the main calcium sensors mediating SNARE-dependent exocytosis in mouse chromaffin cells, but the role of a closely related calcium-binding protein, Doc2b, remains enigmatic. We investigated its role in chromaffin cells using Doc2b knock-out mice and high temporal resolution measurements of exocytosis. We found that the calcium dependence of vesicle priming and release triggering remained unchanged, ruling out an obligatory role for Doc2b in those processes. However, in the absence of Doc2b, release was shifted from the readily releasable pool to the subsequent sustained component. Conversely, upon overexpression of Doc2b, the sustained component was largely inhibited whereas the readily releasable pool was augmented. Electron microscopy revealed an increase in the total number of vesicles upon Doc2b overexpression, ruling out vesicle depletion as the cause for the reduced sustained component. Further experiments showed that, in the absence of Doc2b, the refilling of the readily releasable vesicle pools is faster, but incomplete. Faster refilling leads to an increase in the sustained component as newly primed vesicles fuse while the [Ca(2+)]i following stimulation is still high. We conclude that Doc2b acts to inhibit vesicle priming during prolonged calcium elevations, thus protecting unprimed vesicles from fusing prematurely, and redirecting them to refill the readily releasable pool after relaxation of the calcium signal. In sum, Doc2b favors fast, synchronized release, and limits out-of-phase secretion.
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31
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Walter AM, Pinheiro PS, Verhage M, Sørensen JB. A sequential vesicle pool model with a single release sensor and a Ca(2+)-dependent priming catalyst effectively explains Ca(2+)-dependent properties of neurosecretion. PLoS Comput Biol 2013; 9:e1003362. [PMID: 24339761 PMCID: PMC3854459 DOI: 10.1371/journal.pcbi.1003362] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2013] [Accepted: 10/09/2013] [Indexed: 12/23/2022] Open
Abstract
Neurotransmitter release depends on the fusion of secretory vesicles with the plasma membrane and the release of their contents. The final fusion step displays higher-order Ca2+ dependence, but also upstream steps depend on Ca2+. After deletion of the Ca2+ sensor for fast release – synaptotagmin-1 – slower Ca2+-dependent release components persist. These findings have provoked working models involving parallel releasable vesicle pools (Parallel Pool Models, PPM) driven by alternative Ca2+ sensors for release, but no slow release sensor acting on a parallel vesicle pool has been identified. We here propose a Sequential Pool Model (SPM), assuming a novel Ca2+-dependent action: a Ca2+-dependent catalyst that accelerates both forward and reverse priming reactions. While both models account for fast fusion from the Readily-Releasable Pool (RRP) under control of synaptotagmin-1, the origins of slow release differ. In the SPM the slow release component is attributed to the Ca2+-dependent refilling of the RRP from a Non-Releasable upstream Pool (NRP), whereas the PPM attributes slow release to a separate slowly-releasable vesicle pool. Using numerical integration we compared model predictions to data from mouse chromaffin cells. Like the PPM, the SPM explains biphasic release, Ca2+-dependence and pool sizes in mouse chromaffin cells. In addition, the SPM accounts for the rapid recovery of the fast component after strong stimulation, where the PPM fails. The SPM also predicts the simultaneous changes in release rate and amplitude seen when mutating the SNARE-complex. Finally, it can account for the loss of fast- and the persistence of slow release in the synaptotagmin-1 knockout by assuming that the RRP is depleted, leading to slow and Ca2+-dependent fusion from the NRP. We conclude that the elusive ‘alternative Ca2+ sensor’ for slow release might be the upstream priming catalyst, and that a sequential model effectively explains Ca2+-dependent properties of secretion without assuming parallel pools or sensors. The release of neurotransmitter involves the rapid Ca2+-dependent fusion of vesicles with the plasma membrane. Kinetic heterogeneity is ubiquitous in secretory systems, with fast phases of release on the millisecond time scale being followed by slower phases. In the absence of synaptotagmin-1 – the Ca2+sensor for fast fusion – the fast phase of release is absent, while slower phases remain. To account for this, mathematical models incorporated several releasable vesicle pools with separate Ca2+ sensors. However, there is no clear evidence for parallel release pathways. We suggest a sequential model for Ca2+-dependent neurotransmitter release in adrenal chromaffin cells. We assume only a single releasable vesicle pool, and a Ca2+-dependent catalytic refilling process from a limited upstream vesicle pool. This model can produce kinetic heterogeneity and does better than the previous Parallel Pool Model in predicting the Ca2+-dependence of releasable pool refilling and the consequences of SNARE-protein mutation. It further accounts for the release in the absence of synaptotagmin-1 by assuming that the releasable vesicle pool is depleted, leading to slow and Ca2+-dependent fusion from the upstream pool, but through the same release pathway. Thus, we suggest that the elusive ‘alternative Ca2+ sensor’ is an upstream priming protein, rather than a parallel Ca2+ sensor.
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Affiliation(s)
- Alexander M. Walter
- Department of Functional Genomics and Department of Clinical Genetics, Center for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, VU University Amsterdam and VU University Medical Center, Amsterdam, The Netherlands
- Department of Neuroscience and Pharmacology, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark
- * E-mail: (AMW) (AW); (JBS) (JS)
| | - Paulo S. Pinheiro
- Department of Neuroscience and Pharmacology, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark
- Lundbeck Foundation Center for Biomembranes in Nanomedicine, University of Copenhagen, Copenhagen, Denmark
| | - Matthijs Verhage
- Department of Functional Genomics and Department of Clinical Genetics, Center for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, VU University Amsterdam and VU University Medical Center, Amsterdam, The Netherlands
| | - Jakob B. Sørensen
- Department of Neuroscience and Pharmacology, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark
- Lundbeck Foundation Center for Biomembranes in Nanomedicine, University of Copenhagen, Copenhagen, Denmark
- * E-mail: (AMW) (AW); (JBS) (JS)
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32
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Cabeza JM, Acosta J, Alés E. Mechanisms of granule membrane recapture following exocytosis in intact mast cells. J Biol Chem 2013; 288:20293-305. [PMID: 23709219 DOI: 10.1074/jbc.m113.459065] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In secretory cells, several exocytosis-coupled forms of endocytosis have been proposed including clathrin-mediated endocytosis, kiss-and-run endocytosis, cavicapture, and bulk endocytosis. These forms of endocytosis can be induced under different conditions, but their detailed molecular mechanisms and functions are largely unknown. We studied exocytosis and endocytosis in mast cells with both perforated-patch and whole-cell configurations of the patch clamp technique using cell capacitance measurements in combination with amperometric serotonin detection. We found that intact mast cells exhibit an early endocytosis that follows exocytosis induced by compound 48/80. Direct observation of individual exocytic and endocytic events showed a higher percentage of capacitance flickers (27.3%) and off-steps (11.4%) in intact mast cells than in dialyzed cells (5.4% and 2.9%, respectively). Moreover, we observed a type of endocytosis of large pieces of membrane that were likely formed by cumulative fusion of several secretory granules with the cell membrane. We also identified "large-capacitance flickers" that occur after large endocytosis events. Pore conductance analysis indicated that these transient events may represent "compound cavicapture," most likely due to the flickering of a dilated fusion pore. Using fluorescence imaging of individual exocytic and endocytic events we observed that granules can fuse to granules already fused with the plasma membrane, and then the membranes and dense cores of fused granules are internalized. Altogether, our results suggest that stimulated exocytosis in intact mast cells is followed by several forms of compensatory endocytosis, including kiss-and-run endocytosis and a mechanism for efficient retrieval of the compound membrane of several secretory granules through a single membrane fission event.
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Affiliation(s)
- Jose M Cabeza
- Departamento de Fisiología Médica y Biofísica, Facultad de Medicina, Universidad de Sevilla, 41009 Sevilla, Spain
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Fernández-Morales JC, Arranz-Tagarro JA, Calvo-Gallardo E, Maroto M, Padín JF, García AG. Stabilizers of neuronal and mitochondrial calcium cycling as a strategy for developing a medicine for Alzheimer's disease. ACS Chem Neurosci 2012; 3:873-83. [PMID: 23173068 DOI: 10.1021/cn3001069] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2012] [Accepted: 08/29/2012] [Indexed: 12/21/2022] Open
Abstract
For the last two decades, most efforts on new drug development to treat Alzheimer's disease have been focused to inhibit the synthesis of amyloid beta (Aβ), to prevent Aβ deposition, or to clear up Aβ plaques from the brain of Alzheimer's disease (AD) patients. Other pathogenic mechanisms such as the hyperphosphorylation of the microtubular tau protein (that forms neurofibrillary tangles) have also been addressed as, for instance, with inhibitors of the enzyme glycogen synthase-3 kinase beta (GSK3β). However, in spite of their proven efficacy in animal models of AD, all these compounds have so far failed in clinical trials done in AD patients. It seems therefore desirable to explore new concepts and strategies in the field of drug development for AD. We analyze here our hypothesis that a trifunctional chemical entity acting on the L subtype of voltage-dependent Ca(2+) channels (VDCCs) and on the mitochondrial Na(+)/Ca(2+) exchanger (MNCX), and having additional antioxidant properties, may efficiently delay or stop the death of vulnerable neurons in the brain of AD patients. In recent years, evidence has accumulated indicating that enhanced neuronal Ca(2+) cycling (NCC) and futile mitochondrial Ca(2+) cycling (MCC) are central stage in activating calpain and calcineurin, as well as the intrinsic mitochondrial pathway for apoptosis, leading to death of vulnerable neurons. An additional contributing factor to neuronal death is the excess free radical production linked to distortion of Ca(2+) homeostasis. We propose that an hybrid compound containing a dihydropyridine moiety (to block L channels and mitigate Ca(2+) entry) and a benzothiazepine moiety (to block the MNCX and slow down the rate of Ca(2+) efflux from the mitochondrial matrix into the cytosol), as well as a polyphenol moiety (to sequester excess free radicals) could break down the pathological enhanced NCC and MCC, thus delaying the initiation of apoptosis and the death of vulnerable neurons. In so doing, such a trifunctional compound could eventually become a neuroprotective medicine capable of delaying disease progression in AD patients.
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Affiliation(s)
| | - Juan-Alberto Arranz-Tagarro
- Departamento de Farmacología,
Facultad de Farmacia, Universidad de Santiago de Compostela, Santiago de Compostela, Spain
| | | | | | | | - Antonio G. García
- Servicio de Farmacología
Clínica, Instituto de Investigación Sanitaria, Hospital Universitario de La Princesa, Madrid, Spain
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Kasai H, Takahashi N, Tokumaru H. Distinct Initial SNARE Configurations Underlying the Diversity of Exocytosis. Physiol Rev 2012; 92:1915-64. [DOI: 10.1152/physrev.00007.2012] [Citation(s) in RCA: 120] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The dynamics of exocytosis are diverse and have been optimized for the functions of synapses and a wide variety of cell types. For example, the kinetics of exocytosis varies by more than five orders of magnitude between ultrafast exocytosis in synaptic vesicles and slow exocytosis in large dense-core vesicles. However, in all cases, exocytosis is mediated by the same fundamental mechanism, i.e., the assembly of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins. It is often assumed that vesicles need to be docked at the plasma membrane and SNARE proteins must be preassembled before exocytosis is triggered. However, this model cannot account for the dynamics of exocytosis recently reported in synapses and other cells. For example, vesicles undergo exocytosis without prestimulus docking during tonic exocytosis of synaptic vesicles in the active zone. In addition, epithelial and hematopoietic cells utilize cAMP and kinases to trigger slow exocytosis of nondocked vesicles. In this review, we summarize the manner in which the diversity of exocytosis reflects the initial configurations of SNARE assembly, including trans-SNARE, binary-SNARE, unitary-SNARE, and cis-SNARE configurations. The initial SNARE configurations depend on the particular SNARE subtype (syntaxin, SNAP25, or VAMP), priming proteins (Munc18, Munc13, CAPS, complexin, or snapin), triggering proteins (synaptotagmins, Doc2, and various protein kinases), and the submembraneous cytomatrix, and they are the key to determining the kinetics of subsequent exocytosis. These distinct initial configurations will help us clarify the common SNARE assembly processes underlying exocytosis and membrane trafficking in eukaryotic cells.
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Affiliation(s)
- Haruo Kasai
- Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan; and Faculty of Pharmaceutical Sciences at Kagawa, Tokushima Bunri University, Kagawa, Japan
| | - Noriko Takahashi
- Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan; and Faculty of Pharmaceutical Sciences at Kagawa, Tokushima Bunri University, Kagawa, Japan
| | - Hiroshi Tokumaru
- Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan; and Faculty of Pharmaceutical Sciences at Kagawa, Tokushima Bunri University, Kagawa, Japan
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Padín JF, de Diego AM, Fernández-Morales JC, Merino C, Maroto M, Calvo-Gallardo E, Arranz JA, Yáñez M, García AG. Resveratrol augments nitric oxide generation and causes store calcium release in chromaffin cells. Eur J Pharmacol 2012; 685:99-107. [DOI: 10.1016/j.ejphar.2012.03.040] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2011] [Revised: 03/16/2012] [Accepted: 03/23/2012] [Indexed: 12/29/2022]
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Pasche M, Matti U, Hof D, Rettig J, Becherer U. Docking of LDCVs is modulated by lower intracellular [Ca2+] than priming. PLoS One 2012; 7:e36416. [PMID: 22590540 PMCID: PMC3349663 DOI: 10.1371/journal.pone.0036416] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2012] [Accepted: 03/31/2012] [Indexed: 11/23/2022] Open
Abstract
Many regulatory steps precede final membrane fusion in neuroendocrine cells. Some parts of this preparatory cascade, including fusion and priming, are dependent on the intracellular Ca(2+) concentration ([Ca(2+)](i)). However, the functional implications of [Ca(2+)](i) in the regulation of docking remain elusive and controversial due to an inability to determine the modulatory effect of [Ca(2+)](i). Using a combination of TIRF-microscopy and electrophysiology we followed the movement of large dense core vesicles (LDCVs) close to the plasma membrane, simultaneously measuring membrane capacitance and [Ca(2+)](i). We found that a free [Ca(2+)](i) of 700 nM maximized the immediately releasable pool and minimized the lateral mobility of vesicles, which is consistent with a maximal increase of the pool size of primed LDCVs. The parameters that reflect docking, i.e. axial mobility and the fraction of LDCVs residing at the plasma membrane for less than 5 seconds, were strongly decreased at a free [Ca(2+)](i) of 500 nM. These results provide the first evidence that docking and priming occur at different free intracellular Ca(2+) concentrations, with docking efficiency being the most robust at 500 nM.
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Affiliation(s)
- Mathias Pasche
- Physiologisches Institut, Universität des Saarlandes, Homburg/Saar, Germany
| | - Ulf Matti
- Physiologisches Institut, Universität des Saarlandes, Homburg/Saar, Germany
| | - Detlef Hof
- Physiologisches Institut, Universität des Saarlandes, Homburg/Saar, Germany
| | - Jens Rettig
- Physiologisches Institut, Universität des Saarlandes, Homburg/Saar, Germany
| | - Ute Becherer
- Physiologisches Institut, Universität des Saarlandes, Homburg/Saar, Germany
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Cytosolic organelles shape calcium signals and exo–endocytotic responses of chromaffin cells. Cell Calcium 2012; 51:309-20. [DOI: 10.1016/j.ceca.2011.12.004] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2011] [Revised: 12/02/2011] [Accepted: 12/05/2011] [Indexed: 01/09/2023]
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Mitochondria and chromaffin cell function. Pflugers Arch 2012; 464:33-41. [PMID: 22278417 DOI: 10.1007/s00424-012-1074-2] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2011] [Revised: 01/05/2012] [Accepted: 01/09/2012] [Indexed: 10/14/2022]
Abstract
Chromaffin cells are an excellent model for stimulus-secretion coupling. Ca(2+) entry through plasma membrane voltage-operated Ca(2+) channels (VOCC) is the trigger for secretion, but the intracellular organelles contribute subtle nuances to the Ca(2+) signal. The endoplasmic reticulum amplifies the cytosolic Ca(2+) ([Ca(2+)](C)) signal by Ca(2+)-induced Ca(2+) release (CICR) and helps generation of microdomains with high [Ca(2+)](C) (HCMD) at the subplasmalemmal region. These HCMD induce exocytosis of the docked secretory vesicles. Mitochondria close to VOCC take up large amounts of Ca(2+) from HCMD and stop progression of the Ca(2+) wave towards the cell core. On the other hand, the increase of [Ca(2+)] at the mitochondrial matrix stimulates respiration and tunes energy production to the increased needs of the exocytic activity. At the end of stimulation, [Ca(2+)](C) decreases rapidly and mitochondria release the Ca(2+) accumulated in the matrix through the Na(+)/Ca(2+) exchanger. VOCC, CICR sites and nearby mitochondria form functional triads that co-localize at the subplasmalemmal area, where secretory vesicles wait ready for exocytosis. These triads optimize stimulus-secretion coupling while avoiding propagation of the Ca(2+) signal to the cell core. Perturbation of their functioning in neurons may contribute to the genesis of excitotoxicity, ageing mental retardation and/or neurodegenerative disorders.
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Borges R, Domínguez N, Estévez-Herrera J, Pereda D, Machado JD. Vesicular Ca(2+) mediates granule motion and exocytosis. Cell Calcium 2012; 51:338-41. [PMID: 22222091 DOI: 10.1016/j.ceca.2011.12.009] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2011] [Revised: 12/05/2011] [Accepted: 12/08/2011] [Indexed: 10/14/2022]
Abstract
Secretory vesicles of chromaffin cells are acidic organelles that maintain an increasing pH gradient towards the cytosol (5.5 vs. 7.3) that is mediated by V-ATPase activity. This gradient is primarily responsible for the accumulation of large concentrations of amines and Ca(2+), although the mechanisms mediating Ca(2+) uptake and release from granules, and the physiological relevance of these processes, remain unclear. The presence of a vesicular matrix appears to create a bi-compartmentalised medium in which the major fractions of solutes, including catecholamines, nucleotides and Ca(2+), are strongly associated with vesicle proteins, particularly chromogranins. This association appears to be favoured at acidic pH values. It has been demonstrated that disrupting the pH gradient of secretory vesicles reduces their rate of exocytosis and promotes the leakage of vesicular amines and Ca(2+), dramatically increasing the movement of secretory vesicles and triggering exocytosis. In this short review, we will discuss the data available that highlights the importance of pH in regulating the association between chromogranins, vesicular amines and Ca(2+). We will also address the potential role of vesicular Ca(2+) in two major processes in secretory cells, vesicle movement and exocytosis.
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Affiliation(s)
- Ricardo Borges
- Unidad de Farmacología, Facultad de Medicina, Universidad de La Laguna, Tenerife, Spain.
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Lindau M. High resolution electrophysiological techniques for the study of calcium-activated exocytosis. Biochim Biophys Acta Gen Subj 2011; 1820:1234-42. [PMID: 22209782 DOI: 10.1016/j.bbagen.2011.12.011] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2011] [Revised: 12/09/2011] [Accepted: 12/10/2011] [Indexed: 11/30/2022]
Abstract
BACKGROUND Neurotransmitters, neuropeptides and hormones are released from secretory vesicles of nerve terminals and neuroendocrine cells by calcium-activated exocytosis. A key step in this process is the formation of a fusion pore between the vesicle membrane and the plasma membrane. Exocytotic fusion leads to an increase in plasma membrane area that can be measured as a proportional increase in plasma membrane capacitance. SCOPE OF REVIEW High resolution capacitance measurements in single cells, nerve terminals and small membrane patches have become possible with the development of the patch clamp technique. This review discusses the methods of whole cell patch clamp capacitance measurements and their use in conjunction with voltage clamp pulse stimulation and with stimulation by photorelease of caged calcium. It also discusses patch capacitance measurements for the study of single exocytotic events and fusion pore properties in neuroendocrine cells and nerve terminals. MAJOR CONCLUSIONS Capacitance measurements provide high resolution information on the extent and time course of fusion for the characterization of vesicle pools and the kinetics of exocytosis. They allow the characterization of the mode of fusion including distinction of single vesicle full fusion, transient kiss-and-run fusion or multivesicular compound exocytosis. Furthermore, measurement of fusion pore conductances and their dynamic behavior has enabled the characterization of fusion pore properties in a way that resembles the characterization of ion channel function through single channel recordings. GENERAL SIGNIFICANCE The combination of patch clamp capacitance measurements with pharmacological and molecular manipulations of exocytosis is emerging as a powerful approach to investigate the molecular mechanisms of calcium-activated exocytotic fusion pore formation. This article is part of a Special Issue entitled Biochemical, biophysical and genetic approaches to intracellular calcium signalling.
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Affiliation(s)
- Manfred Lindau
- School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14853, USA.
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Machado JD, Camacho M, Alvarez J, Borges R. On the role of intravesicular calcium in the motion and exocytosis of secretory organelles. Commun Integr Biol 2011; 2:71-3. [PMID: 19704891 DOI: 10.4161/cib.7467] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2008] [Accepted: 11/20/2008] [Indexed: 11/19/2022] Open
Abstract
Secretory vesicles of sympathetic neurons and chromaffin granules maintain a pH gradient towards the cytosol (5.5 vs. 7.2) promoted by the V-ATPase activity. This gradient of pH is mainly responsible for the accumulation of amines. The secretory vesicles contain large amounts of total Ca(2+), but the free intragranular [Ca(2+)], the mechanisms for Ca(2+) uptake and release from the granules and their physiological relevance regarding exocytosis are still matters of debate.We have recently shown that disruption of the pH gradient of secretory vesicles slowed down exocytosis. Fluorimetric measurements, using the dye Oregon green BAPTA-2, showed that the V-ATPase inhibitor bafilomycin A1 directly released Ca(2+) from freshly isolated vesicles. Accordingly, vesicle alkalinization released Ca(2+) from the granules to the cytosol, measured with fura-2 in intact chromaffin cells. Using TIRFM in cells overexpressing the EGFP-labeled synaptobrevin (VAMP2-EGFP) protein, we have then shown that the Ca(2+) released from the vesicles to the cytosol in the presence of bafilomycin, dramatically increased the granule motion of chromaffin- or PC12-derived granules, and triggered exocytosis (measured by amperometry).We conclude that the gradient of pH of secretory vesicles might be involved in the homeostatic regulation of the local cytosolic Ca(2+) around the vesicles and in two of the major functions of secretory cells, vesicle motion and exocytosis.1.
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Affiliation(s)
- José D Machado
- Unidad de Farmacología; Facultad de Medicina; Universidad de La Laguna Tenerife; La Laguna, Spain
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Milla J, Montesinos MS, Machado JD, Borges R, Alonso E, Moreno-Ortega AJ, Cano-Abad MF, García AG, Ruiz-Nuño A. Ouabain enhances exocytosis through the regulation of calcium handling by the endoplasmic reticulum of chromaffin cells. Cell Calcium 2011; 50:332-42. [PMID: 21741086 DOI: 10.1016/j.ceca.2011.06.002] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2010] [Revised: 05/23/2011] [Accepted: 06/09/2011] [Indexed: 11/18/2022]
Abstract
The augmentation of neurotransmitter and hormone release produced by ouabain inhibition of plasmalemmal Na+/K+-ATPase (NKA) is well established. However, the mechanism underlying this action is still controversial. Here we have shown that in bovine adrenal chromaffin cells ouabain diminished the mobility of chromaffin vesicles, an indication of greater number of docked vesicles at subplasmalemmal exocytotic sites. On the other hand, ouabain augmented the number of vesicles undergoing exocytosis in response to a K+ pulse, rather than the quantal size of single vesicles. Furthermore, ouabain produced a tiny and slow Ca2+ release from the endoplasmic reticulum (ER) and gradually augmented the transient elevations of the cytosolic Ca2+ concentrations ([Ca2+]c) triggered by K+ pulses. These effects were paralleled by gradual increments of the transient catecholamine release responses triggered by sequential K+ pulses applied to chromaffin cell populations treated with ouabain. Both, the increases of K+-elicited [Ca2+]c and secretion in ouabain-treated cells were blocked by thapsigargin (THAPSI), 2-aminoethoxydiphenyl borate (2-APB) and caffeine. These results are compatible with the view that ouabain may enhance the ER Ca2+ load and facilitate the Ca2+-induced-Ca2+ release (CICR) component of the [Ca2+]c signal generated during K+ depolarisation. This could explain the potentiating effects of ouabain on exocytosis.
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Affiliation(s)
- Juan Milla
- Instituto Teófilo Hernando, Departamento de Farmacología y Terapéutica, Facultad de Medicina, Universidad Autónoma de Madrid, and Servicio de Farmacología Clínica, Instituto de Investigación Sanitaria, Hospital Universitario de la Princesa, Madrid, Spain
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Zhang B, Sun L, Yang YM, Huang HP, Zhu FP, Wang L, Zhang XY, Guo S, Zuo PL, Zhang CX, Ding JP, Wang LY, Zhou Z. Action potential bursts enhance transmitter release at a giant central synapse. J Physiol 2011; 589:2213-27. [PMID: 21486773 DOI: 10.1113/jphysiol.2010.200154] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Patterns of action potentials (APs), often in the form of bursts, are critical for coding and processing information in the brain. However, how AP bursts modulate secretion at synapses remains elusive. Here, using the calyx of Held synapse as a model we compared synaptic release evoked by AP patterns with a different number of bursts while the total number of APs and frequency were fixed. The ratio of total release produced by multiple bursts to that by a single burst was defined as 'burst-effect'.We found that four bursts of 25 stimuli at 100 Hz increased the totalcharge of EPSCs to 1.47 ± 0.04 times that by a single burst of 100 stimuli at the same frequency.Blocking AMPA receptor desensitization and saturation did not alter the burst-effect, indicating that it was mainly determined by presynaptic mechanisms. Simultaneous dual recordings of presynaptic membrane capacitance (Cm) and EPSCs revealed a similar burst-effect, being 1.58±0.13by Cm and 1.49±0.05 by EPSCs. Reducing presynapticCa2+ influx by lowering extracellular Ca2+concentration or buffering residual intracellular Ca2+ with EGTA inhibited the burst-effect. We further developed a computational model largely recapitulating the burst-effect and demonstrated that this effect is highly sensitive to dynamic change in availability of the releasable pool of synaptic vesicles during various patterns of activities. Taken together, we conclude that AP bursts modulate synaptic output mainly through intricate interaction between depletion and replenishment of the large releasable pool. This burst-effect differs from the somatic burst-effect previously described from adrenal chromaffin cells, which substantially depends on activity-induced accumulation of Ca2+ to facilitate release of a limited number of vesicles in the releasable pool. Hence, AP bursts may play an important role in dynamically regulating synaptic strength and fidelity during intense neuronal activity at central synapses.
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Affiliation(s)
- Bo Zhang
- Institute of Molecular Medicine, Peking University, Beijing 100871, China
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Gutiérrez-Martín Y, Bustillo D, Gómez-Villafuertes R, Sánchez-Nogueiro J, Torregrosa-Hetland C, Binz T, Gutiérrez LM, Miras-Portugal MT, Artalejo AR. P2X7 receptors trigger ATP exocytosis and modify secretory vesicle dynamics in neuroblastoma cells. J Biol Chem 2011; 286:11370-81. [PMID: 21292765 PMCID: PMC3064193 DOI: 10.1074/jbc.m110.139410] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
Previously, we reported that purinergic ionotropic P2X7 receptors negatively regulate neurite formation in Neuro-2a (N2a) mouse neuroblastoma cells through a Ca2+/calmodulin-dependent kinase II-related mechanism. In the present study we used this cell line to investigate a parallel though faster P2X7 receptor-mediated signaling pathway, namely Ca2+-regulated exocytosis. Selective activation of P2X7 receptors evoked exocytosis as assayed by high resolution membrane capacitance measurements. Using dual-wavelength total internal reflection microscopy, we have observed both the increase in near-membrane Ca2+ concentration and the exocytosis of fluorescently labeled vesicles in response to P2X7 receptor stimulation. Moreover, activation of P2X7 receptors also affects vesicle motion in the vertical and horizontal directions, thus, involving this receptor type in the control of early steps (docking and priming) of the secretory pathway. Immunocytochemical and RT-PCR experiments evidenced that N2a cells express the three neuronal SNAREs as well as vesicular nucleotide and monoamine (VMAT-1 and VMAT-2) transporters. Biochemical measurements indicated that ionomycin induced a significant release of ATP from N2a cells. Finally, P2X7 receptor stimulation and ionomycin increased the incidence of small transient inward currents, reminiscent of postsynaptic quantal events observed at synapses. Small transient inward currents were dependent on extracellular Ca2+ and were abolished by Brilliant Blue G, suggesting they were mediated by P2X7 receptors. Altogether, these results suggest the existence of a positive feedback mechanism mediated by P2X7 receptor-stimulated exocytotic release of ATP that would act on P2X7 receptors on the same or neighbor cells to further stimulate its own release and negatively control N2a cell differentiation.
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Abstract
PURPOSE To investigate changes in cytokine levels in tears of type 2 diabetics with or without retinopathy. METHODS Tears were collected from 15 type 2 diabetics without retinopathy (DNR), 15 patients with retinopathy (DR), and 15 age and gender matched non-diabetic controls. Tear concentrations of 27 cytokines were measured by multiplex bead immunoassay. Cytokine differences between groups, ratios of type-1 T helper (Th1)/type-2 T helper (Th2) cytokines and anti-angiogenic/pro-angiogenic cytokines were analyzed statistically. RESULTS The most abundant cytokine detected in tears was interferon-induced protein-10 (IP-10). In comparison with controls, IP-10 and monocyte chemoattracant protein-1 (MCP-1) levels were significantly elevated in DR (p=0.016 and 0.036, respectively) and DNR groups (p=0.021 and 0.026, respectively). Interleukin-1 (IL-1) receptor antagonist (IL-1ra) levels were significantly increased in DNR (p=0.016). Th1/Th2 cytokines interferon-gamma (IFN-γ)/IL-5 and IL-2/IL-5 ratios were significantly increased in DR compared to controls (p=0.037 and 0.031, respectively). Anti-angiogenic/angiogenic cytokines IFN-γ/MCP-1 and IL-4/MCP-1 ratios in DR and DNR were significantly decreased compared to controls (p<0.05). IL-4/IL-8 and IL-12p70/IL-8 ratios were also significantly decreased in DR compared to controls (p=0.02 and 0.045, respectively). No significant correlation was demonstrated between tear cytokine concentrations and glycosylated hemoglobin (HbA1c) or fasting plasma glucose (FPG). CONCLUSIONS Diabetic tears exhibited elevated levels of IP-10 and MCP-1. The Th1/Th2 cytokine balance may shift to a predominantly Th1 state in DR patients. Pro-angiogenic cytokines are more highly represented than anti-angiogenic cytokines in the tears of diabetic patients.
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Schonn JS, Van Weering JRT, Mohrmann R, Schlüter OM, Südhof TC, De Wit H, Verhage M, Sørensen JB. Rab3 Proteins Involved in Vesicle Biogenesis and Priming in Embryonic Mouse Chromaffin Cells. Traffic 2010; 11:1415-28. [DOI: 10.1111/j.1600-0854.2010.01107.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Abstract
Synaptic vesicle 2 (SV2) proteins, critical for proper nervous system function, are implicated in human epilepsy, yet little is known about their function. We demonstrate, using direct approaches, that loss of the major SV2 isoform in a central nervous system nerve terminal is associated with an elevation in both resting and evoked presynaptic Ca(2+) signals. This increase is essential for the expression of the SV2B(-/-) secretory phenotype, characterized by changes in synaptic vesicle dynamics, synaptic plasticity, and synaptic strength. Short-term reproduction of the Ca(2+) phenotype in wild-type nerve terminals reproduces almost all aspects of the SV2B(-/-) secretory phenotype, while rescue of the Ca(2+) phenotype in SV2B(-/-) neurons relieves every facet of the SV2B(-/-) secretory phenotype. Thus, SV2 controls key aspects of synaptic functionality via its ability to regulate presynaptic Ca(2+), suggesting a potential new target for therapeutic intervention in the treatment of epilepsy.
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Greater cytosolic and mitochondrial calcium transients in adrenal medullary slices of hypertensive, compared with normotensive rats. Eur J Pharmacol 2010; 636:126-36. [DOI: 10.1016/j.ejphar.2010.03.044] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2009] [Revised: 03/01/2010] [Accepted: 03/13/2010] [Indexed: 11/19/2022]
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Petrovic J, Walsh PL, Thornley KT, Miller CE, Wightman RM. Real-time monitoring of chemical transmission in slices of the murine adrenal gland. Endocrinology 2010; 151:1773-83. [PMID: 20181796 PMCID: PMC2850225 DOI: 10.1210/en.2009-1324] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
The real-time electrochemical detection of catecholamine secretion from murine adrenal slices using fast-scan cyclic voltammetry (FSCV) and amperometry at carbon fiber microelectrodes is described. Bright-field and immunofluorescent microscopy supported that chromaffin cells in the adrenal medulla are organized into clusters and positively stain for tyrosine hydroxylase confirming that they are catecholaminergic. Spontaneous exocytotic catecholamine events were observed inside chromaffin cell clusters with both FSCV and amperometry and were modulated by the nicotinic acetylcholine receptor antagonist hexamethonium and low extracellular calcium. Reintroduction of extracellular calcium and pressure ejection of acetylcholine caused the frequency of spikes to increase back to predrug levels. Electrical stimulation caused the synchronous secretion from multiple cells within the gland, which were modulated by nicotinic acetylcholine receptors but not muscarinic receptors or gap junctions. Furthermore, electrically stimulated release was abolished with perfusion of low extracellular calcium or tetrodotoxin, indicating that the release requires electrical excitability. An extended waveform was used to study the spontaneous and stimulated release events to determine their chemical content by FSCV. Consistent with total content analysis and immunohistochemical studies, about two thirds of the cells studied spontaneously secreted epinephrine, whereas one third secreted norepinephrine. Whereas adrenergic sites contained mostly epinephrine during electrical stimulation, noradrenergic sites contained a mixture of the catecholamines showing the heterogeneity of the adrenal medulla.
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Affiliation(s)
- Jelena Petrovic
- Neuroscience Center (R.M.W.), Caudill Laboratories, Venable Hall B-5, CB 3290, Chapel Hill, North Carolina 27599-3290, USA
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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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