1
|
Mosharov EV, Lindau M. Patch Amperometry and Intracellular Patch Electrochemistry. Methods Mol Biol 2023; 2565:239-260. [PMID: 36205899 PMCID: PMC9910029 DOI: 10.1007/978-1-0716-2671-9_17] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Both patch amperometry (PA) and intracellular patch electrochemistry (IPE) take advantage of a recording configuration where an electrochemical detector-carbon fiber electrode (CFE)-is housed inside a patch pipette. PA, which is employed in cell-attached or excised inside-out patch clamp configuration, offers high-resolution patch capacitance measurements with simultaneous amperometric detection of catecholamines released during exocytosis. The method provides precise information on single-vesicle size and quantal content, fusion pore conductance, and permeability of the pore for catecholamines. IPE, on the other hand, measures cytosolic catecholamines that diffuse into the patch pipette following membrane rupture to achieve the whole-cell configuration. In amperometric mode, IPE detects total catechols, whereas in cyclic voltammetric mode, it provides more specific information on the nature of the detected molecules and may selectively quantify catecholamines, providing a direct approach to determine cytosolic concentrations of catecholaminergic transmitters and their metabolites. Here, we provide detailed instructions on setting up PA and IPE, performing experiments and analyzing the data.
Collapse
Affiliation(s)
- Eugene V. Mosharov
- Departments of Psychiatry and Neurology, Columbia University Medical Center, New York State Psychiatric Institute, New York, NY 10032
| | - Manfred Lindau
- Department of Physiology and Biophysics, University of Miami, Miller School of Medicine, Miami, FL, 33136
| |
Collapse
|
2
|
Guérineau NC, Campos P, Le Tissier PR, Hodson DJ, Mollard P. Cell Networks in Endocrine/Neuroendocrine Gland Function. Compr Physiol 2022; 12:3371-3415. [PMID: 35578964 DOI: 10.1002/cphy.c210031] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Reproduction, growth, stress, and metabolism are determined by endocrine/neuroendocrine systems that regulate circulating hormone concentrations. All these systems generate rhythms and changes in hormone pulsatility observed in a variety of pathophysiological states. Thus, the output of endocrine/neuroendocrine systems must be regulated within a narrow window of effective hormone concentrations but must also maintain a capacity for plasticity to respond to changing physiological demands. Remarkably most endocrinologists still have a "textbook" view of endocrine gland organization which has emanated from 20th century histological studies on thin 2D tissue sections. However, 21st -century technological advances, including in-depth 3D imaging of specific cell types have vastly changed our knowledge. We now know that various levels of multicellular organization can be found across different glands, that organizational motifs can vary between species and can be modified to enhance or decrease hormonal release. This article focuses on how the organization of cells regulates hormone output using three endocrine/neuroendocrine glands that present different levels of organization and complexity: the adrenal medulla, with a single neuroendocrine cell type; the anterior pituitary, with multiple intermingled cell types; and the pancreas with multiple intermingled cell types organized into distinct functional units. We give an overview of recent methodologies that allow the study of the different components within endocrine systems, particularly their temporal and spatial relationships. We believe the emerging findings about network organization, and its impact on hormone secretion, are crucial to understanding how homeostatic regulation of endocrine axes is carried out within endocrine organs themselves. © 2022 American Physiological Society. Compr Physiol 12:3371-3415, 2022.
Collapse
Affiliation(s)
| | - Pauline Campos
- College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, UK
| | - Paul R Le Tissier
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh, Scotland, UK
| | - David J Hodson
- Institute of Metabolism and Systems Research (IMSR), University of Birmingham, Edgbaston, UK.,Centre for Endocrinology, Diabetes and Metabolism, Birmingham Health Partners, Birmingham, UK.,COMPARE University of Birmingham and University of Nottingham Midlands, UK.,Oxford Centre for Diabetes, Endocrinology and Metabolism (OCDEM), NIHR Oxford Biomedical Research Centre, Churchill Hospital, Radcliffe Department of Medicine, University of Oxford, Oxford, UK
| | - Patrice Mollard
- IGF, University of Montpellier, CNRS, INSERM, Montpellier, France
| |
Collapse
|
3
|
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]
|
4
|
An Alternative Exon of CAPS2 Influences Catecholamine Loading into LDCVs of Chromaffin Cells. J Neurosci 2019; 39:18-27. [PMID: 30389842 DOI: 10.1523/jneurosci.2040-18.2018] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2018] [Revised: 10/01/2018] [Accepted: 10/27/2018] [Indexed: 11/21/2022] Open
Abstract
The calcium-dependent activator proteins for secretion (CAPS) are priming factors for synaptic and large dense-core vesicles (LDCVs), promoting their entry into and stabilizing the release-ready state. A modulatory role of CAPS in catecholamine loading of vesicles has been suggested. Although an influence of CAPS on monoamine transporter function and on vesicle acidification has been reported, a role of CAPS in vesicle loading is disputed. Using expression of naturally occurring splice variants of CAPS2 into chromaffin cells from CAPS1/CAPS2 double-deficient mice of both sexes, we show that an alternative exon of 40 aa is responsible for enhanced catecholamine loading of LDCVs in mouse chromaffin cells. The presence of this exon leads to increased activity of both vesicular monoamine transporters. Deletion of CAPS does not alter acidification of vesicles. Our results establish a splice-variant-dependent modulatory effect of CAPS on catecholamine content in LDCVs.SIGNIFICANCE STATEMENT The calcium activator protein for secretion (CAPS) promotes and stabilizes the entry of catecholamine-containing vesicles of the adrenal gland into a release-ready state. Expression of an alternatively spliced exon in CAPS leads to enhanced catecholamine content in chromaffin granules. This exon codes for 40 aa with a high proline content, consistent with an unstructured loop present in the portion of the molecule generally thought to be involved in vesicle priming. CAPS variants containing this exon promote serotonin uptake into Chinese hamster ovary cells expressing either vesicular monoamine transporter. Epigenetic tuning of CAPS variants may allow modulation of endocrine adrenaline and noradrenaline release. This mechanism may extend to monoamine release in central neurons or in the enteric nervous system.
Collapse
|
5
|
Estévez-Herrera J, Domínguez N, Pardo MR, González-Santana A, Westhead EW, Borges R, Machado JD. ATP: The crucial component of secretory vesicles. Proc Natl Acad Sci U S A 2016; 113:E4098-106. [PMID: 27342860 PMCID: PMC4948319 DOI: 10.1073/pnas.1600690113] [Citation(s) in RCA: 57] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The colligative properties of ATP and catecholamines demonstrated in vitro are thought to be responsible for the extraordinary accumulation of solutes inside chromaffin cell secretory vesicles, although this has yet to be demonstrated in living cells. Because functional cells cannot be deprived of ATP, we have knocked down the expression of the vesicular nucleotide carrier, the VNUT, to show that a reduction in vesicular ATP is accompanied by a drastic fall in the quantal release of catecholamines. This phenomenon is particularly evident in newly synthesized vesicles, which we show are the first to be released. Surprisingly, we find that inhibiting VNUT expression also reduces the frequency of exocytosis, whereas the overexpression of VNUT drastically increases the quantal size of exocytotic events. To our knowledge, our data provide the first demonstration that ATP, in addition to serving as an energy source and purinergic transmitter, is an essential element in the concentration of catecholamines in secretory vesicles. In this way, cells can use ATP to accumulate neurotransmitters and other secreted substances at high concentrations, supporting quantal transmission.
Collapse
Affiliation(s)
- Judith Estévez-Herrera
- Unidad de Farmacología, Facultad de Medicina, Universidad de la Laguna, Tenerife 38320, Spain
| | - Natalia Domínguez
- Unidad de Farmacología, Facultad de Medicina, Universidad de la Laguna, Tenerife 38320, Spain
| | - Marta R Pardo
- Unidad de Farmacología, Facultad de Medicina, Universidad de la Laguna, Tenerife 38320, Spain; Instituto Universitario de Bio-Orgánica 'Antonio González', Universidad de la Laguna, Tenerife 38320, Spain
| | - Ayoze González-Santana
- Unidad de Farmacología, Facultad de Medicina, Universidad de la Laguna, Tenerife 38320, Spain
| | - Edward W Westhead
- Unidad de Farmacología, Facultad de Medicina, Universidad de la Laguna, Tenerife 38320, Spain
| | - Ricardo Borges
- Unidad de Farmacología, Facultad de Medicina, Universidad de la Laguna, Tenerife 38320, Spain; Instituto Universitario de Bio-Orgánica 'Antonio González', Universidad de la Laguna, Tenerife 38320, Spain
| | - José David Machado
- Unidad de Farmacología, Facultad de Medicina, Universidad de la Laguna, Tenerife 38320, Spain
| |
Collapse
|
6
|
Abstract
Protein Interacting with C Kinase 1 (PICK1) is a Bin/Amphiphysin/Rvs (BAR) domain protein involved in AMPA receptor trafficking. Here, we identify a selective role for PICK1 in the biogenesis of large, dense core vesicles (LDCVs) in mouse chromaffin cells. PICK1 colocalized with syntaxin-6, a marker for immature granules. In chromaffin cells isolated from a PICK1 knockout (KO) mouse the amount of exocytosis was reduced, while release kinetics and Ca(2+) sensitivity were unaffected. Vesicle-fusion events had a reduced frequency and released lower amounts of transmitter per vesicle (i.e., reduced quantal size). This was paralleled by a reduction in the mean single-vesicle capacitance, estimated by averaging time-locked capacitance traces. EM confirmed that LDCVs were fewer and of markedly reduced size in the PICK1 KO, demonstrating that all phenotypes can be explained by reductions in vesicle number and size, whereas the fusion competence of generated vesicles was unaffected by the absence of PICK1. Viral rescue experiments demonstrated that long-term re-expression of PICK1 is necessary to restore normal vesicular content and secretion, while short-term overexpression is ineffective, consistent with an upstream role for PICK1. Disrupting lipid binding of the BAR domain (2K-E mutation) or of the PDZ domain (CC-GG mutation) was sufficient to reproduce the secretion phenotype of the null mutant. The same mutations are known to eliminate PICK1 function in receptor trafficking, indicating that the multiple functions of PICK1 involve a conserved mechanism. Summarized, our findings demonstrate that PICK1 functions in vesicle biogenesis and is necessary to maintain normal vesicle numbers and size.
Collapse
|
7
|
Weiss AN, Bittner MA, Holz RW, Axelrod D. Protein mobility within secretory granules. Biophys J 2014; 107:16-25. [PMID: 24988337 PMCID: PMC4478961 DOI: 10.1016/j.bpj.2014.04.063] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2013] [Revised: 02/14/2014] [Accepted: 04/11/2014] [Indexed: 10/25/2022] Open
Abstract
We investigated the basis for previous observations that fluorescent-labeled neuropeptide Y (NPY) is usually released within 200 ms after fusion, whereas labeled tissue plasminogen activator (tPA) is often discharged over many seconds. We found that tPA and NPY are endogenously expressed in small and different subpopulations of bovine chromaffin cells in culture. We measured the mobility of these proteins (tagged with fluorophore) within the lumen of individual secretory granules in living chromaffin cells, and related their mobilities to postfusion release kinetics. A method was developed that is not limited by standard optical resolution, in which a bright flash of strongly decaying evanescent field (∼64 nm exponential decay constant) produced by total internal reflection (TIR) selectively bleaches cerulean-labeled protein proximal to the glass coverslip within individual granules. Fluorescence recovery occurred as unbleached protein from distal regions within the 300 nm granule diffused into the bleached proximal regions. The fractional bleaching of tPA-cerulean (tPA-cer) was greater when subsequently probed with TIR excitation than with epifluorescence, indicating that tPA-cer mobility was low. The almost equal NPY-cer bleaching when probed with TIR and epifluorescence indicated that NPY-cer equilibrated within the 300 ms bleach pulse, and therefore had a greater mobility than tPA-cer. TIR-fluorescence recovery after photobleaching revealed a significant recovery of tPA-cer (but not NPY-cer) fluorescence within several hundred milliseconds after bleaching. Numerical simulations, which take into account bleach duration, granule diameter, and the limited number of fluorophores in a granule, are consistent with tPA-cer being 100% mobile, with a diffusion coefficient of 2 × 10(-10) cm(2)/s (∼1/3000 of that for a protein of similar size in aqueous solution). However, the low diffusive mobility of tPA cannot alone explain its slow postfusion release. In the accompanying study, we suggest that, additionally, tPA itself stabilizes the fusion pore with dimensions that restrict its own exit.
Collapse
Affiliation(s)
| | - Mary A Bittner
- Department of Pharmacology, University of Michigan, Ann Arbor, Michigan
| | - Ronald W Holz
- Department of Pharmacology, University of Michigan, Ann Arbor, Michigan.
| | - Daniel Axelrod
- Department of Pharmacology, University of Michigan, Ann Arbor, Michigan; Department of Physics and LSA Biophysics, University of Michigan, Ann Arbor, Michigan
| |
Collapse
|
8
|
Poëa-Guyon S, Ammar MR, Erard M, Amar M, Moreau AW, Fossier P, Gleize V, Vitale N, Morel N. The V-ATPase membrane domain is a sensor of granular pH that controls the exocytotic machinery. ACTA ACUST UNITED AC 2013; 203:283-98. [PMID: 24165939 PMCID: PMC3812966 DOI: 10.1083/jcb.201303104] [Citation(s) in RCA: 80] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Several studies have suggested that the V0 domain of the vacuolar-type H(+)-adenosine triphosphatase (V-ATPase) is directly implicated in secretory vesicle exocytosis through a role in membrane fusion. We report in this paper that there was a rapid decrease in neurotransmitter release after acute photoinactivation of the V0 a1-I subunit in neuronal pairs. Likewise, inactivation of the V0 a1-I subunit in chromaffin cells resulted in a decreased frequency and prolonged kinetics of amperometric spikes induced by depolarization, with shortening of the fusion pore open time. Dissipation of the granular pH gradient was associated with an inhibition of exocytosis and correlated with the V1-V0 association status in secretory granules. We thus conclude that V0 serves as a sensor of intragranular pH that controls exocytosis and synaptic transmission via the reversible dissociation of V1 at acidic pH. Hence, the V-ATPase membrane domain would allow the exocytotic machinery to discriminate fully loaded and acidified vesicles from vesicles undergoing neurotransmitter reloading.
Collapse
Affiliation(s)
- Sandrine Poëa-Guyon
- Centre de Neurosciences Paris-Sud, Centre National de la Recherche Scientifique Unité Mixte de Recherche 8195 and Université Paris-Sud, F-91405 Orsay, France
| | | | | | | | | | | | | | | | | |
Collapse
|
9
|
Neuropeptide y gates a stress-induced, long-lasting plasticity in the sympathetic nervous system. J Neurosci 2013; 33:12705-17. [PMID: 23904607 DOI: 10.1523/jneurosci.3132-12.2013] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Acute stress evokes the fight-or-flight reflex, which via release of the catecholamine hormones affects the function of every major organ. Although the reflex is transient, it has lasting consequences that produce an exaggerated response when stress is reexperienced. How this change is encoded is not known. We investigated whether the reflex affects the adrenal component of the sympathetic nervous system, a major branch of the stress response. Mice were briefly exposed to the cold-water forced swim test (FST) which evoked an increase in circulating catecholamines. Although this hormonal response was transient, the FST led to a long-lasting increase in the catecholamine secretory capacity measured amperometrically from chromaffin cells and in the expression of tyrosine hydroxylase. A variety of approaches indicate that these changes are regulated postsynaptically by neuropeptide Y (NPY), an adrenal cotransmitter. Using immunohistochemistry, RT-PCR, and NPY(GFP) BAC mice, we find that NPY is synthesized by all chromaffin cells. Stress failed to increase secretory capacity in NPY knock-out mice. Genetic or pharmacological interference with NPY and Y1 (but not Y2 or Y5) receptor signaling attenuated the stress-induced change in tyrosine hydroxylase expression. These results indicate that, under basal conditions, adrenal signaling is tonically inhibited by NPY, but stress overrides this autocrine negative feedback loop. Because acute stress leads to a lasting increase in secretory capacity in vivo but does not alter sympathetic tone, these postsynaptic changes appear to be an adaptive response. We conclude that the sympathetic limb of the stress response exhibits an activity-dependent form of long-lasting plasticity.
Collapse
|
10
|
Wang L, Tu P, Bonet L, Aubrey KR, Supplisson S. Cytosolic transmitter concentration regulates vesicle cycling at hippocampal GABAergic terminals. Neuron 2013; 80:143-58. [PMID: 24094108 DOI: 10.1016/j.neuron.2013.07.021] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/19/2013] [Indexed: 10/26/2022]
Abstract
Sustained synaptic transmission requires vesicle recycling and refilling with transmitter, two processes considered to proceed independently. Contrary to this assumption, we show here that depletion of cytosolic transmitter at GABAergic synapses reversibly reduces the number of recycling vesicles. Using paired recordings in hippocampal cultures, we show that repetitive activity causes two phases of reduction of the postsynaptic response. The first involves the classical depletion of the readily releasable and recycling pools, while the second reflects impairment of vesicle filling as GABA is consumed, since it can only be reversed by uptake of GABA or its precursors, glutamate or glutamine. Surprisingly, this second phase is associated with reduced quantal release, a faster depression rate and lower FM5-95 labeling, suggesting that the size of the cycling vesicular pool is regulated by cytosolic transmitter availability. Regulation of vesicular cycling may represent a general mechanism of presynaptic plasticity, matching synaptic release to transmitter supply.
Collapse
Affiliation(s)
- Lu Wang
- INSERM, U1024, F-75005 Paris, France; CNRS, UMR 8197, F-75005 Paris, France; Ecole Normale Supérieure, Institut de Biologie de l'ENS, IBENS, F-75005 Paris, France; Shanghai Key Laboratory of Brain Functional Genomics, East China Normal University, 200062 Shanghai, China
| | | | | | | | | |
Collapse
|
11
|
Wegrzyn JL, Bark SJ, Funkelstein L, Mosier C, Yap A, Kazemi-Esfarjani P, La Spada AR, Sigurdson C, O'Connor DT, Hook V. Proteomics of dense core secretory vesicles reveal distinct protein categories for secretion of neuroeffectors for cell-cell communication. J Proteome Res 2010; 9:5002-24. [PMID: 20695487 DOI: 10.1021/pr1003104] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Regulated secretion of neurotransmitters and neurohumoral factors from dense core secretory vesicles provides essential neuroeffectors for cell-cell communication in the nervous and endocrine systems. This study provides comprehensive proteomic characterization of the categories of proteins in chromaffin dense core secretory vesicles that participate in cell-cell communication from the adrenal medulla. Proteomic studies were conducted by nano-HPLC Chip MS/MS tandem mass spectrometry. Results demonstrate that these secretory vesicles contain proteins of distinct functional categories consisting of neuropeptides and neurohumoral factors, protease systems, neurotransmitter enzymes and transporters, receptors, enzymes for biochemical processes, reduction/oxidation regulation, ATPases, protein folding, lipid biochemistry, signal transduction, exocytosis, calcium regulation, as well as structural and cell adhesion proteins. The secretory vesicle proteomic data identified 371 proteins in the soluble fraction and 384 membrane proteins, for a total of 686 distinct secretory vesicle proteins. Notably, these proteomic analyses illustrate the presence of several neurological disease-related proteins in these secretory vesicles, including huntingtin interacting protein, cystatin C, ataxin 7, and prion protein. Overall, these findings demonstrate that multiple protein categories participate in dense core secretory vesicles for production, storage, and secretion of bioactive neuroeffectors for cell-cell communication in health and disease.
Collapse
Affiliation(s)
- Jill L Wegrzyn
- Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, La Jolla, California 92093, USA
| | | | | | | | | | | | | | | | | | | |
Collapse
|
12
|
Neco P, Fernández-Peruchena C, Navas S, Gutiérrez LM, de Toledo GA, Alés E. Myosin II contributes to fusion pore expansion during exocytosis. J Biol Chem 2008; 283:10949-57. [PMID: 18283106 DOI: 10.1074/jbc.m709058200] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
During exocytosis, the fusion pore expands to allow release of neurotransmitters and hormones to the extracellular space. To understand the process of synaptic transmission, it is of outstanding importance to know the properties of the fusion pore and how these properties affect the release process. Many proteins have been implicated in vesicle fusion; however, there is little evidence for proteins involved in fusion pore expansion. Myosin II has been shown to participate in the transport of vesicles and, surprisingly, in the final phases of exocytosis, affecting the kinetics of catecholamine release in adrenal chromaffin cells as measured by amperometry. Here, we have studied single vesicle exocytosis in chromaffin cells overexpressing an unphosphorylatable form (T18AS19A RLC-GFP) of myosin II that produces an inactive protein by patch amperometry. This method allows direct determination of fusion pore expansion by measuring its conductance, whereas the release of catecholamines is recorded simultaneously by amperometry. Here we demonstrated that the fusion pore is of critical importance to control the release of catecholamines during single vesicle secretion in chromaffin cells. We proved that myosin II acts as a molecular motor on the fusion pore expansion by hindering its dilation when it lacks the phosphorylation sites.
Collapse
Affiliation(s)
- Patricia Neco
- Departamento Fisiología Médica y Biofísica, Universidad de Sevilla, Sevilla 41009, Spain
| | | | | | | | | | | |
Collapse
|
13
|
Borges R, Camacho M, Gillis KD. Measuring secretion in chromaffin cells using electrophysiological and electrochemical methods. Acta Physiol (Oxf) 2008; 192:173-84. [PMID: 18021323 DOI: 10.1111/j.1748-1716.2007.01814.x] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Our present understanding of exocytosis of catecholamines has benefited tremendously from the arrival of single-cell electrochemical methods (amperometry and voltammetry), electrophysiological techniques (whole-cell and patch capacitance) and from the combination of both techniques (patch amperometry). In this brief review, we will outline the strengths and limitations of amperometric and electrophysiological methods and highlight the major contribution obtained with the use of these techniques in chromaffin cells.
Collapse
Affiliation(s)
- R Borges
- Unidad de Farmacología, Facultad de Medicina, Universidad de La Laguna, Tenerife, Spain.
| | | | | |
Collapse
|
14
|
Abstract
Exocytosis occurs via fusion of secretory granules with the cell membrane, whereupon the granule content is at least partially released and the granule membrane is temporarily added to the plasma membrane. Exocytosis is balanced by compensatory endocytosis to achieve net equilibrium of the cell surface area and to recycle and redistribute components of the exocytosis machinery. The underlying molecular mechanisms remain a matter of debate. In this review, we summarize and discuss recent progress in the understanding of compensatory endocytosis, with the focus on chromaffin cells as a useful model for studying mechanisms of regulated secretion.
Collapse
Affiliation(s)
- S Barg
- Department of Cell Biology, Division of Medicine, Imperial College, London, UK.
| | | |
Collapse
|
15
|
Carabelli V, Marcantoni A, Comunanza V, de Luca A, Díaz J, Borges R, Carbone E. Chronic hypoxia up-regulates alpha1H T-type channels and low-threshold catecholamine secretion in rat chromaffin cells. J Physiol 2007; 584:149-65. [PMID: 17690152 PMCID: PMC2277059 DOI: 10.1113/jphysiol.2007.132274] [Citation(s) in RCA: 89] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2007] [Accepted: 08/03/2007] [Indexed: 12/24/2022] Open
Abstract
alpha(1H) T-type channels recruited by beta(1)-adrenergic stimulation in rat chromaffin cells (RCCs) are coupled to fast exocytosis with the same Ca(2+) dependence of high-threshold Ca(2+) channels. Here we show that RCCs exposed to chronic hypoxia (CH) for 12-18 h in 3% O(2) express comparable densities of functional T-type channels that depolarize the resting cells and contribute to low-voltage exocytosis. Following chronic hypoxia, most RCCs exhibited T-type Ca(2+) channels already available at -50 mV with the same gating, pharmacological and molecular features as the alpha(1H) isoform. Chronic hypoxia had no effects on cell size and high-threshold Ca(2+) current density and was mimicked by overnight incubation with the iron-chelating agent desferrioxamine (DFX), suggesting the involvement of hypoxia-inducible factors (HIFs). T-type channel recruitment occurred independently of PKA activation and the presence of extracellular Ca(2+). Hypoxia-recruited T-type channels were partially open at rest (T-type 'window-current') and contributed to raising the resting potential to more positive values. Their block by 50 microm Ni(2+) caused a 5-8 mV hyperpolarization. The secretory response associated with T-type channels could be detected following mild cell depolarizations, either by capacitance increases induced by step depolarizations or by amperometric current spikes induced by increased [KCl]. In the latter case, exocytotic bursts could be evoked even with 2-4 mm KCl and spike frequency was drastically reduced by 50 microm Ni(2+). Chronic hypoxia did not alter the shape of spikes, suggesting that hypoxia-recruited T-type channels increase the number of secreted vesicles at low voltages, without altering the mechanism of catecholamine release and the quantal content of released molecules.
Collapse
Affiliation(s)
- V Carabelli
- Department of Neuroscience, NIS Center of Excellence, CNISM Research Unit, 10125 Torino, Italy
| | | | | | | | | | | | | |
Collapse
|
16
|
Tabares L, Ruiz R, Linares-Clemente P, Gaffield MA, Alvarez de Toledo G, Fernandez-Chacón R, Betz WJ. Monitoring synaptic function at the neuromuscular junction of a mouse expressing synaptopHluorin. J Neurosci 2007; 27:5422-30. [PMID: 17507564 PMCID: PMC6672353 DOI: 10.1523/jneurosci.0670-07.2007] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
We monitored presynaptic exocytosis and vesicle recycling at neuromuscular junctions of transgenic mice expressing synaptopHluorin (spH), using simultaneous optical and electrophysiological recordings. Synaptic transmission was indistinguishable from that in wild-type controls. Fluorescence rose during and decayed monotonically after stimulus trains to the nerve, with amplitudes and decay times increasing with the amount of stimulation. The relatively large size of synaptic terminals allowed us to examine the spatial profile of fluorescence changes. We identified hot spots of exocytosis, which were stable with repeated trains. Photobleach experiments showed that spH freshly exposed by nerve stimulation was not preferentially retrieved by compensatory endocytosis; instead, most retrieved spH preexisted in the surface membrane. Finally, we compared fluorescence and electrical [summed end-plate potentials (EPPs)] estimates of exocytosis, which diverged during repeated trains, as fluorescence exceeded summed EPPs, although the average amplitude of miniature EPPs was unchanged. This might reflect exocytosis of spH-containing, acetylcholine-free ("empty") vesicles or other organelles during intense stimulation.
Collapse
Affiliation(s)
- Lucia Tabares
- Department of Medical Physiology and Biophysics, School of Medicine, University of Seville, 41009 Seville, Spain.
| | | | | | | | | | | | | |
Collapse
|
17
|
Dernick G, Gong LW, Tabares L, Alvarez de Toledo G, Lindau M. Patch amperometry: high-resolution measurements of single-vesicle fusion and release. Nat Methods 2005; 2:699-708. [PMID: 16118641 DOI: 10.1038/nmeth0905-699] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Gregor Dernick
- School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14850, USA
| | | | | | | | | |
Collapse
|
18
|
Hafez I, Kisler K, Berberian K, Dernick G, Valero V, Yong MG, Craighead HG, Lindau M. Electrochemical imaging of fusion pore openings by electrochemical detector arrays. Proc Natl Acad Sci U S A 2005; 102:13879-84. [PMID: 16172395 PMCID: PMC1236545 DOI: 10.1073/pnas.0504098102] [Citation(s) in RCA: 109] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Opening of individual exocytotic fusion pores in chromaffin cells was imaged electrochemically with high time resolution. Electrochemical detector arrays that consist of four platinum microelectrodes were microfabricated on a glass coverslip. Exocytosis of single vesicles containing catecholamines from a cell positioned on top of the array is detected by the individual electrodes as a time-resolved oxidation current, reflecting the time course of arrival of catecholamine molecules at the electrode surfaces. The signals exhibit low noise and reveal foot signals indicating fusion pore formation and expansion. The position of individual release events is determined from the fraction of catecholamines recorded by the individual electrodes. Simultaneous fluorescence imaging of release of acridine orange from individual vesicles confirmed the electrochemical position assignments. This electrochemical camera provides very high time resolution, spatiotemporal localization of individual fusion pore openings and quantitative data on the flux of transmitter from individual vesicles. Analysis of the amperometric currents employing random walk simulations indicates that the time course of amperometric spikes measured near the cell surface is due to a low apparent diffusion coefficient of catecholamines near the cell surface and not due to slow dissociation from the granular matrix.
Collapse
Affiliation(s)
- Ismail Hafez
- School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14853, USA
| | | | | | | | | | | | | | | |
Collapse
|
19
|
Obermüller S, Lindqvist A, Karanauskaite J, Galvanovskis J, Rorsman P, Barg S. Selective nucleotide-release from dense-core granules in insulin-secreting cells. J Cell Sci 2005; 118:4271-82. [PMID: 16141231 DOI: 10.1242/jcs.02549] [Citation(s) in RCA: 113] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Secretory granules of insulin-secreting cells are used to store and release peptide hormones as well as low-molecular-weight compounds such as nucleotides. Here we have compared the rate of exocytosis with the time courses of nucleotide and peptide release by a combination of capacitance measurements, electrophysiological detection of ATP release and single-granule imaging. We demonstrate that the release of nucleotides and peptides is delayed by approximately 0.1 and approximately 2 seconds with respect to membrane fusion, respectively. We further show that in up to 70% of the cases exocytosis does not result in significant release of the peptide cargo, likely because of a mechanism that leads to premature closure of the fusion pore. Release of nucleotides and protons occurred regardless of whether peptides were secreted or not. These observations suggest that insulin-secreting cells are able to use the same secretory vesicles to release small molecules either alone or together with the peptide hormone.
Collapse
Affiliation(s)
- Stefanie Obermüller
- Department of Experimental Medicinal Sciences, Lund University, BMC B11, SE-221 84 Lund, Sweden
| | | | | | | | | | | |
Collapse
|
20
|
Speidel D, Bruederle CE, Enk C, Voets T, Varoqueaux F, Reim K, Becherer U, Fornai F, Ruggieri S, Holighaus Y, Weihe E, Bruns D, Brose N, Rettig J. CAPS1 regulates catecholamine loading of large dense-core vesicles. Neuron 2005; 46:75-88. [PMID: 15820695 DOI: 10.1016/j.neuron.2005.02.019] [Citation(s) in RCA: 96] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2004] [Revised: 11/13/2004] [Accepted: 02/09/2005] [Indexed: 11/27/2022]
Abstract
CAPS1 is thought to play an essential role in mediating exocytosis from large dense-core vesicles (LDCVs). We generated CAPS1-deficient (KO) mice and studied exocytosis in a model system for Ca2+-dependent LDCV secretion, the adrenal chromaffin cell. Adult heterozygous CAPS1 KO cells display a gene dosage-dependent decrease of CAPS1 expression and a concomitant reduction in the number of docked vesicles and secretion. Embryonic homozygous CAPS1 KO cells show a strong reduction in the frequency of amperometrically detectable release events of transmitter-filled vesicles, while the total number of fusing vesicles, as judged by capacitance recordings or total internal reflection microscopy, remains unchanged. We conclude that CAPS1 is required for an essential step in the uptake or storage of catecholamines in LDCVs.
Collapse
Affiliation(s)
- Dina Speidel
- Max-Planck-Institut für Experimentelle Medizin, Abteilung Molekulare Neurobiologie, D-37075 Göttingen, Germany
| | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
21
|
Abstract
Ca2+-dependent activator protein for secretion (CAPS) is an evolutionarily conserved secretory protein that was previously thought to mediate Ca2+-triggered fusion of dense-core vesicles. In an elegant study of CAPS1-deficient mice, Speidel et al. (this issue of Neuron) now show that CAPS function may have been misunderstood. CAPS appears to act upstream of fusion in the biogenesis or maintenance of mature secretory vesicles, raising the possibility of a completely new type of function for an essential component of the secretory machinery.
Collapse
Affiliation(s)
- Thomas C Südhof
- Center for Basic Neuroscience, Department of Molecular Genetics and Howard Hughes Medical Institute, UT Southwestern Medical Center, 6000 Harry Hines Boulevard, NA4.118, Dallas, Texas 75390, USA
| |
Collapse
|
22
|
Taupenot L, Harper KL, O'Connor DT. Role of H+-ATPase-mediated acidification in sorting and release of the regulated secretory protein chromogranin A: evidence for a vesiculogenic function. J Biol Chem 2004; 280:3885-97. [PMID: 15542860 DOI: 10.1074/jbc.m408197200] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The constitutive and regulated secretory pathways represent the classical routes for secretion of proteins from neuroendocrine cells. Selective aggregation of secretory granule constituents in an acidic, bivalent cation-rich environment is considered to be a prerequisite for sorting to the regulated secretory pathway. The effect of selective vacuolar H+-ATPase (V-ATPase) inhibitor bafilomycin A1 on the pH gradient along the secretory pathway was used here to study the role of acidification on the trafficking of the regulated secretory protein chromogranin A (CgA) in PC12 cells. Sorting of CgA was assessed by three-dimensional deconvolution microscopy, subcellular fractionation, and secretagogue-stimulated release, examining a series of full-length or truncated domains of human CgA (CgA-(1-115), CgA-(233-439)) fused to either green fluorescent protein or to a novel form of secreted embryonic alkaline phosphatase (EAP). We show that a full-length CgA/EAP chimera is sorted to chromaffin granules for exocytosis. Inhibition of V-ATPase by bafilomycin A1 markedly reduced the secretagogue-stimulated release of CgA-EAP by perturbing sorting of the chimera (at the trans-Golgi network or immature secretory granule) rather than the late steps of exocytosis. The effect of bafilomycin A1 on CgA secretion depends on a sorting determinant located within the amino terminus (CgA-(1-115)) but not the C-terminal region of the granin. Moreover, examination of chromaffin granule abundance in PC12 cells exposed to bafilomycin A1 reveals a substantial decrease in the number of dense-core vesicles. We propose that a V-ATPase-mediated pH gradient in the secretory pathway is an important factor for the formation of dense-core granules by regulating the ability of CgA to form aggregates, a crucial step that may underlie the granulogenic function of the protein.
Collapse
Affiliation(s)
- Laurent Taupenot
- Department of Medicine and Center for Molecular Genetics, University of California at San Diego, La Jolla, California 92093, USA.
| | | | | |
Collapse
|
23
|
Croft BG, Fortin GD, Corera AT, Edwards RH, Beaudet A, Trudeau LE, Fon EA. Normal biogenesis and cycling of empty synaptic vesicles in dopamine neurons of vesicular monoamine transporter 2 knockout mice. Mol Biol Cell 2004; 16:306-15. [PMID: 15496457 PMCID: PMC539174 DOI: 10.1091/mbc.e04-07-0559] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The neuronal isoform of vesicular monoamine transporter, VMAT2, is responsible for packaging dopamine and other monoamines into synaptic vesicles and thereby plays an essential role in dopamine neurotransmission. Dopamine neurons in mice lacking VMAT2 are unable to store or release dopamine from their synaptic vesicles. To determine how VMAT2-mediated filling influences synaptic vesicle morphology and function, we examined dopamine terminals from VMAT2 knockout mice. In contrast to the abnormalities reported in glutamatergic terminals of mice lacking VGLUT1, the corresponding vesicular transporter for glutamate, we found that the ultrastructure of dopamine terminals and synaptic vesicles in VMAT2 knockout mice were indistinguishable from wild type. Using the activity-dependent dyes FM1-43 and FM2-10, we also found that synaptic vesicles in dopamine neurons lacking VMAT2 undergo endocytosis and exocytosis with kinetics identical to those seen in wild-type neurons. Together, these results demonstrate that dopamine synaptic vesicle biogenesis and cycling are independent of vesicle filling with transmitter. By demonstrating that such empty synaptic vesicles can cycle at the nerve terminal, our study suggests that physiological changes in VMAT2 levels or trafficking at the synapse may regulate dopamine release by altering the ratio of fillable-to-empty synaptic vesicles, as both continue to cycle in response to neural activity.
Collapse
Affiliation(s)
- Benjamin G Croft
- Centre for Neuronal Survival and Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec H3A 2B4, Canada
| | | | | | | | | | | | | |
Collapse
|
24
|
Perrais D, Kleppe IC, Taraska JW, Almers W. Recapture after exocytosis causes differential retention of protein in granules of bovine chromaffin cells. J Physiol 2004; 560:413-28. [PMID: 15297569 PMCID: PMC1665250 DOI: 10.1113/jphysiol.2004.064410] [Citation(s) in RCA: 138] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2004] [Accepted: 08/04/2004] [Indexed: 11/08/2022] Open
Abstract
After exocytosis, chromaffin granules release essentially all their catecholamines in small fractions of a second, but it is unknown how fast they release stored peptides and proteins. Here we compare the exocytic release of fluorescently labelled neuropeptide Y (NPY) and tissue plasminogen activator from single granules. Exocytosis was tracked by measuring the membrane capacitance, and single granules in live cells were imaged by evanescent field microscopy. Neuropeptide Y left most granules in small fractions of a second, while tissue plasminogen activator remained in open granules for minutes. Taking advantage of the dependence on pH of the fluorescence of green fluorescent protein, we used rhythmic external acidification to determine whether and when granules re-sealed. One-third of them re-sealed within 100 s and retained significant levels of tissue plasminogen activator. Re-sealing accounts for only a fraction of the endocytosis monitored in capacitance measurements. When external [Ca2+] was raised, even neuropeptide Y remained in open granules until they re-sealed. It is concluded that a significant fraction of chromaffin granules re-seal after exocytosis, and retain those proteins that leave granules slowly. We suggest that granules vary the stoichiometry of release by varying both granule re-sealing and the association of proteins with the granule matrix.
Collapse
Affiliation(s)
- David Perrais
- Vollum Institute, Oregon Health & Science University, 3181 SW Sam Jackson Park Road, Portland, OR 97239-3098, USA
| | | | | | | |
Collapse
|
25
|
Abstract
The number of transmitter molecules released in a quantal event can be regulated, and recent studies suggest that the modulation of quantal size is associated with corresponding changes in vesicle volume (Colliver et al., 2000; Pothos et al., 2002). If so, this could occur either by distension of the vesicle membrane or by incorporation and removal of vesicle membrane. We performed simultaneous measurements of vesicle membrane area and catecholamine release in individual quantal events from chromaffin cells using cell-attached patch amperometry. Cells were treated with reserpine, a vesicular monoamine transport blocker that decreases quantal size, or l-dopa, a catecholamine precursor that increases quantal size. We show that decrease and increase in quantal size are associated with a respective decrease and increase in vesicle membrane area. These results point to a novel mechanism of vesicle membrane dynamics by which vesicles physically change their membrane area in response to changes in transmitter content such that the intravesicular concentration of transmitter is maintained.
Collapse
|
26
|
Abstract
The secretory process requires many different steps and stages. Vesicles must be formed and transported to the target membrane. They must be tethered or docked at the appropriate sites and must be prepared for fusion (priming). As the last step, a fusion pore is formed and the contents are released. Release of neurotransmitter is an extremely rapid event leading to rise times of the postsynaptic response of less than 100 micro s. The release thus occurs during the initial formation of the exocytotic fusion pore. To understand the process of synaptic transmission, it is thus of outstanding importance to understand the molecular structure of the fusion pore, what are the properties of the initial fusion pore, how these properties affect the release process and what other factors may be limiting the kinetics of release. Here we review the techniques currently employed in fusion pore studies and discuss recent data and opinions on exocytotic fusion pore properties.
Collapse
Affiliation(s)
- Manfred Lindau
- School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14850, USA.
| | | |
Collapse
|
27
|
Carabelli V, Giancippoli A, Baldelli P, Carbone E, Artalejo AR. Distinct potentiation of L-type currents and secretion by cAMP in rat chromaffin cells. Biophys J 2003; 85:1326-37. [PMID: 12885675 PMCID: PMC1303249 DOI: 10.1016/s0006-3495(03)74567-6] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
We have investigated the potentiating action of cAMP on L-currents of rat chromaffin cells and the corresponding increase of Ca(2+)-evoked secretory responses with the aim of separating the action of cAMP on Ca(2+) entry through L-channels and the downstream effects of cAMP/protein kinase A (PKA) on exocytosis. In omega-toxin-treated rat chromaffin cells, exposure to the permeable cAMP analog 8-(4-chlorophenylthio)-adenosine 3',5'-monophosphate (pCPT-cAMP; 1 mM, 30 min) caused a moderate increase of Ca(2+) charge carried through L-channels (19% in 10 mM Ca(2+) at +10 mV) and a drastic potentiation of secretion ( approximately 100%), measured as membrane capacitance increments (deltaC). The apparent Ca(2+) dependency of exocytosis increased with pCPT-cAMP and was accompanied by 83% enhancement of the readily releasable pool of vesicles with no significant change of the probability of release, as evaluated with paired-pulse stimulation protocols. pCPT-cAMP effects could be mimicked by stimulation of beta(1)-adrenoreceptors and reversed by the PKA inhibitor H89, suggesting strict PKA dependence. For short pulses to +10 mV (100 ms), potentiation of exocytosis by pCPT-cAMP was proportional to the quantity of charge entering the cell and occurred independently of whether L, N, or P/Q channels were blocked, suggesting that cAMP acts as a constant amplification factor for secretion regardless of the channel type carrying Ca(2+). Analysis of statistical variations among depolarization-induced capacitance increments indicates that pCPT-cAMP acts downstream of Ca(2+) entry by almost doubling the mean size of unitary exocytic events, most likely as a consequence of an increased granule-to-granule rather than a granule-to-membrane fusion.
Collapse
Affiliation(s)
- V Carabelli
- Dipartimento di Neuroscienze, Unità di Ricerca, Instituto Nazionale Fisica della Materia, 10125 Turin, Italy.
| | | | | | | | | |
Collapse
|
28
|
Gundelfinger ED, Kessels MM, Qualmann B. Temporal and spatial coordination of exocytosis and endocytosis. Nat Rev Mol Cell Biol 2003; 4:127-39. [PMID: 12563290 DOI: 10.1038/nrm1016] [Citation(s) in RCA: 181] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
In secretory cells, exocytosis and compensatory endocytosis are tightly coupled membrane trafficking processes that control the surface area and composition of the plasma membrane. While exocytic and endocytic processes have been studied independently in great detail, at present there is much interest in understanding the mode of their coupling. This review discusses emerging insights into the coupling of these processes, both in the chemical synapses of neurons and in non-neuronal cells.
Collapse
Affiliation(s)
- Eckart D Gundelfinger
- Leibniz Institute for Neurobiology, Department of Neurochemistry and Molecular Biology, Brenneckestr. 6, 39118 Magdeburg, Germany.
| | | | | |
Collapse
|
29
|
Machado JD, Gómez JF, Betancor G, Camacho M, Brioso MA, Borges R. Hydralazine reduces the quantal size of secretory events by displacement of catecholamines from adrenomedullary chromaffin secretory vesicles. Circ Res 2002; 91:830-6. [PMID: 12411398 DOI: 10.1161/01.res.0000039530.30495.6f] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The effects of the antihypertensive agent hydralazine (1 to 100 nmol/L) on the exocytotic process of single adrenal chromaffin cells have been studied using amperometry. Hydralazine does not reduce the frequency of exocytotic spikes but rapidly slows the rate of catecholamine release from individual exocytotic events by reducing the quantal size of catecholamine exocytosis. Confocal and standard epifluorescence microscopy studies show that hydralazine rapidly accumulates within secretory vesicles. The blockade of the vesicular H+ pump with bafilomycin A1 inhibits hydralazine uptake. Experiments with permeabilized cells show that hydralazine displaces catecholamines from secretory vesicles. The drug also displaces vesicular Ca2+, as shown by fura-2 microfluorimetry. These data suggest that hydralazine acts, at least partially, by interfering with the storage of catecholamines. These effects of hydralazine occurred within seconds, and at the tissue concentrations presumably reached in antihypertensive therapy; these concentrations are a thousand times lower than those described for relaxing vascular tissues in vitro. We proposed that these novel effects could explain many of the therapeutic and side effects of this drug that are likely exerted in sympathetic nerve terminals.
Collapse
Affiliation(s)
- José D Machado
- Unidad de Farmacología, Facultad de Medicina, Universidad de La Laguna, Tenerife, Spain
| | | | | | | | | | | |
Collapse
|
30
|
Machado JD, Alonso C, Morales A, Gómez JF, Borges R. Nongenomic regulation of the kinetics of exocytosis by estrogens. J Pharmacol Exp Ther 2002; 301:631-7. [PMID: 11961067 DOI: 10.1124/jpet.301.2.631] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The role of nongenomic action of estrogens on elicited catecholamine secretion and exocytosis kinetics was studied in perfused rat adrenals and in cultured bovine chromaffin cells. 17beta-Estradiol as well as the estrogen receptor modulators raloxifene and LY117018, but not 17alpha-estradiol, inhibited at the micromolar range the catecholamine output elicited by acetylcholine or high potassium. However, these agents failed to modify the secretion elicited by high Ca(2+) in glands treated with the ionophore A-23187 (calcimycin), suggesting that estrogens did not directly act on the secretory machinery. At the single cell level, estrogens modified the kinetics of exocytosis at nanomolar range. All of the drugs tested except 17alpha-estradiol produced a profound slowing down of the exocytosis as measured by amperometry. LY117018 also reduced the granule content of catecholamines. 17beta-Estradiol reduced the intracellular free Ca(2+) but only at micromolar concentrations, whereas nanomolar concentrations increased the cAMP levels. These effects were reproduced with the nonpermeable drug 17beta-estradiol-horseradish peroxidase and antagonized with nanomolar concentrations of the antiestrogen ICI 182,780 (fulvestrant). Our data suggest the presence of membrane sites that regulate both the exocytotic phenomenon and the total catecholamine release with high and low affinity, respectively.
Collapse
Affiliation(s)
- José D Machado
- Unidad de Farmacología, Facultad de Medicina, Universidad de La Laguna, Tenerife, Spain
| | | | | | | | | |
Collapse
|