151
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Raraty M, Ward J, Erdemli G, Vaillant C, Neoptolemos JP, Sutton R, Petersen OH. Calcium-dependent enzyme activation and vacuole formation in the apical granular region of pancreatic acinar cells. Proc Natl Acad Sci U S A 2000; 97:13126-31. [PMID: 11087863 PMCID: PMC27189 DOI: 10.1073/pnas.97.24.13126] [Citation(s) in RCA: 262] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The pancreatic acinar cell produces powerful digestive enzymes packaged in zymogen granules in the apical pole. Ca(2+) signals elicited by acetylcholine or cholecystokinin (CCK) initiate enzyme secretion by exocytosis through the apical membrane. Intracellular enzyme activation is normally kept to a minimum, but in the often-fatal human disease acute pancreatitis, autodigestion occurs. How the enzymes become inappropriately activated is unknown. We monitored the cytosolic Ca(2+) concentration ([Ca(2+)](i)), intracellular trypsin activation, and its localization in isolated living cells with specific fluorescent probes and studied intracellular vacuole formation by electron microscopy as well as quantitative image analysis (light microscopy). A physiological CCK level (10 pM) eliciting regular Ca(2+) spiking did not evoke intracellular trypsin activation or vacuole formation. However, stimulation with 10 nM CCK, evoking a sustained rise in [Ca(2+)](i), induced pronounced trypsin activation and extensive vacuole formation, both localized in the apical pole. Both processes were abolished by preventing abnormal [Ca(2+)](i) elevation, either by preincubation with the specific Ca(2+) chelator 1, 2-bis(O-aminophenoxy)ethane-N,N-N',N'-tetraacetic acid (BAPTA) or by removal of external Ca(2+). CCK hyperstimulation evokes intracellular trypsin activation and vacuole formation in the apical granular pole. Both of these processes are mediated by an abnormal sustained rise in [Ca(2+)](i).
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Affiliation(s)
- M Raraty
- Medical Research Council Secretory Control Research Group, Physiological Laboratory, and Departments of Surgery and Veterinary Preclinical Sciences, University of Liverpool, Liverpool L69 3BX, United Kingdom
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152
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Park MK, Petersen OH, Tepikin AV. The endoplasmic reticulum as one continuous Ca(2+) pool: visualization of rapid Ca(2+) movements and equilibration. EMBO J 2000; 19:5729-39. [PMID: 11060024 PMCID: PMC305795 DOI: 10.1093/emboj/19.21.5729] [Citation(s) in RCA: 187] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We investigated whether the endoplasmic reticulum (ER) is a functionally connected Ca(2+) store or is composed of separate subunits by monitoring movements of Ca(2+) and small fluorescent probes in the ER lumen of pancreatic acinar cells, using confocal microscopy, local bleaching and uncaging. We observed rapid movements and equilibration of Ca(2+) and the probes. The bulk of the ER at the base was not connected to the granules in the apical part, but diffusion into small apical ER extensions occurred. The connectivity of the ER Ca(2+) store was robust, since even supramaximal acetylcholine (ACh) stimulation for 30 min did not result in functional fragmentation. ACh could elicit a uniform decrease in the ER Ca(2+) concentration throughout the cell, but repetitive cytosolic Ca(2+) spikes, induced by a low ACh concentration, hardly reduced the ER Ca(2+) level. We conclude that the ER is a functionally continuous unit, which enables efficient Ca(2+) liberation. Ca(2+) released from the apical ER terminals is quickly replenished from the bulk of the rough ER at the base.
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Affiliation(s)
- M K Park
- MRC Secretory Control Research Group, The Physiological Laboratory, University of Liverpool, Crown Street, PO Box 147, Liverpool L69 3BX, UK
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153
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Brini M, Bano D, Manni S, Rizzuto R, Carafoli E. Effects of PMCA and SERCA pump overexpression on the kinetics of cell Ca(2+) signalling. EMBO J 2000; 19:4926-35. [PMID: 10990456 PMCID: PMC314231 DOI: 10.1093/emboj/19.18.4926] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2000] [Revised: 07/17/2000] [Accepted: 08/01/2000] [Indexed: 11/15/2022] Open
Abstract
The dynamic interactions of the main pathways for active Ca(2+) transport have been analysed in living cells by altering the expression of their components. The plasma membrane (PMCA) and the endoplasmic reticulum (ER) (SERCA) Ca(2+) pumps were transiently overexpressed in CHO cells, and the Ca(2+) homeostasis in the subcellular compartments was investigated using specifically targeted chimaeras of the Ca(2+)- sensitive photoprotein aequorin. In resting cells, overexpression of the PMCA and SERCA pumps caused a reduction and an increase in ER [Ca(2+)] levels, respectively, while no significant differences were detected in cytosolic and mitochondrial [Ca(2+)]. Upon stimulation with an inositol 1,4, 5-trisphosphate (IP(3))-generating agonist, the amplitude of the mitochondrial and cytosolic Ca(2+) rises correlated with the ER [Ca(2+)] only up to a threshold value, above which the feedback inhibition of the IP(3) channel by Ca(2+) appeared to be limiting.
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Affiliation(s)
- M Brini
- Department of Biochemistry and Center for the Study of Biomembranes of the National Research Council (CNR), University of Padova, Viale G. Colombo, 3, 35121 Padova, Italy.
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154
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Yu R, Hinkle PM. Rapid turnover of calcium in the endoplasmic reticulum during signaling. Studies with cameleon calcium indicators. J Biol Chem 2000; 275:23648-53. [PMID: 10811650 DOI: 10.1074/jbc.m002684200] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
HEK293 cells expressing the thyrotropin-releasing hormone (TRH) receptor were transfected with cameleon Ca(2+) indicators designed to measure the free Ca(2+) concentration in the cytoplasm, [Ca(2+)](cyt), and the endoplasmic reticulum (ER), [Ca(2+)](er). Basal [Ca(2+)](cyt) was about 50 nm; thyrotropin-releasing hormone (TRH) or other agonists increased [Ca(2+)](cyt) to 1 micrometer or higher. Basal [Ca(2+)](er) averaged 500 micrometer and fell to 50-100 micrometer over 10 min in the presence of thapsigargin. TRH consistently decreased [Ca(2+)](er) to 100 micrometer, independent of extracellular Ca(2+), whereas agonists for endogenous receptors generally caused a smaller decline. When added with thapsigargin, all agonists rapidly decreased [Ca(2+)](er) to 5-10 micrometer, indicating that there is substantial store refilling during signaling. TRH increased [Ca(2+)](cyt) and decreased [Ca(2+)](er) if applied after other agonists, whereas other agonists did not alter [Ca(2+)](cyt) or [Ca(2+)](er) if added after TRH. When Ca(2+) was added back to cells that had been incubated with TRH in Ca(2+)-free medium, [Ca(2+)](cyt) and [Ca(2+)](er) increased rapidly. The increase in [Ca(2+)](er) was only partially blocked by thapsigargin but was completely blocked if cells were loaded with 1, 2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid. In conclusion, these new Ca(2+) indicators showed that basal [Ca(2+)](er) is approximately 500 micrometer, that [Ca(2+)](er) has to be >100 micrometer to support an increase in [Ca(2+)](cyt) by agonists, and that during signaling, intracellular Ca(2+) stores are continuously refilled with cytoplasmic Ca(2+) by the sarcoendoplasmic reticulum Ca(2+)-ATPase pump.
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Affiliation(s)
- R Yu
- Department of Pharmacology and Physiology and the Cancer Center, University of Rochester School of Medicine and Dentistry, Rochester, New York 14642, USA
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155
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Abrenica B, Gilchrist JS. Nucleoplasmic Ca(2+)loading is regulated by mobilization of perinuclear Ca(2+). Cell Calcium 2000; 28:127-36. [PMID: 10970769 DOI: 10.1054/ceca.2000.0137] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Regulation of nucleoplasmic calcium (Ca(2+)) concentration may occur by the mobilization of perinuclear luminal Ca(2+)pools involving specific Ca(2+)pumps and channels of both inner and outer perinuclear membranes. To determine the role of perinuclear luminal Ca(2+), we examined freshly cultured 10 day-old embryonic chick ventricular cardiomyocytes. We obtained evidence suggesting the existence of the molecular machinery required for the bi-directional Ca(2+)fluxes using confocal imaging techniques. Embryonic cardiomyocytes were probed with antibodies specific for ryanodine-sensitive Ca(2+)channels (RyR2), sarco/endoplasmic reticulum Ca(2+)ATPase (SERCA2)-pumps, and fluorescent BODIPY derivatives of ryanodine and thapsigargin. Using immunocytochemistry techniques, confocal imaging showed the presence of RyR2 Ca(2+)channels and SERCA2-pumps highly localized to regions surrounding the nucleus, referable to the nuclear envelope. Results obtained from Fluo-3, AM loaded ionomycin-perforated embryonic cardiomyocytes demonstrated that gradual increases of extranuclear Ca(2+)from 100 to 1600 nM Ca(2+)was localized to the nucleus. SERCA2-pump inhibitors thapsigargin and cyclopiazonic acid showed a concentration-dependent inhibition of nuclear Ca(2+)loading. Furthermore, ryanodine demonstrated a biphasic concentration-dependence upon active nuclear Ca(2+)loading. The concomitant addition of thapsigargin or cyclopiazonic acid with ryanodine at inhibitory concentrations caused an significant increase in nuclear Ca(2+)loading at low concentrations of extranuclear added Ca(2+). Our results show that the perinuclear lumen in embryonic chick ventricular cardiomyocytes is capable of autonomously regulating nucleoplasmic Ca(2+)fluxes.
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Affiliation(s)
- B Abrenica
- Department of Oral Biology and Physiology, Division of Stroke and Vascular Disease, University of Manitoba, Winnipeg, Manitoba, Canada
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156
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Callamaras N, Parker I. Phasic characteristic of elementary Ca(2+) release sites underlies quantal responses to IP(3). EMBO J 2000; 19:3608-17. [PMID: 10899115 PMCID: PMC313983 DOI: 10.1093/emboj/19.14.3608] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Ca(2+) liberation by inositol 1,4,5-trisphosphate (IP(3)) is 'quantal', in that low [IP(3)] causes only partial Ca(2+) release, but further increasing [IP(3)] evokes more release. This characteristic allows cells to generate graded Ca(2+) signals, but is unexpected, given the regenerative nature of Ca(2+)-induced Ca(2+) release through IP(3) receptors. Two models have been proposed to resolve this paradox: (i) all-or-none Ca(2+) release from heterogeneous stores that empty at varying [IP(3)]; and (ii) phasic liberation from homogeneously sensitive stores. To discriminate between these hypotheses, we imaged subcellular Ca(2+) puffs evoked by IP(3) in Xenopus oocytes where release sites were functionally uncoupled using EGTA. Puffs were little changed by 300 microM intracellular EGTA, but sites operated autonomously and did not propagate waves. Photoreleased IP(3) generated flurries of puffs-different to the prolonged Ca(2+) elevation following waves in control cells-and individual sites responded repeatedly to successive increments of [IP(3)]. These data support the second hypothesis while refuting the first, and suggest that local Ca(2+) signals exhibit rapid adaptation, different to the slower inhibition following global Ca(2+) waves.
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Affiliation(s)
- N Callamaras
- Laboratory of Cellular and Molecular Neurobiology, Department of Neurobiology and Behavior, University of California Irvine, CA 92697-4550, USA
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157
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McCarron JG, Flynn ER, Bradley KN, Muir TC. Two Ca2+ entry pathways mediate InsP3-sensitive store refilling in guinea-pig colonic smooth muscle. J Physiol 2000; 525 Pt 1:113-24. [PMID: 10811730 PMCID: PMC2269931 DOI: 10.1111/j.1469-7793.2000.00113.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/1999] [Accepted: 02/23/2000] [Indexed: 01/12/2023] Open
Abstract
Sarcolemma Ca2+ influx, necessary for store refilling, was well maintained, over a wide range (-70 to + 40 mV) of membrane voltages, in guinea-pig single circular colonic smooth muscle cells, as indicated by the magnitude of InsP3-evoked Ca2+ transients. This apparent voltage independence of store refilling was achieved by the activity of sarcolemma Ca2+ channels some of which were voltage gated while others were not. At negative membrane potentials (e.g. -70 mV), Ca2+ influx through channels which lacked voltage gating provided for store refilling while at positive membrane potentials (e.g. +40 mV) voltage-gated Ca2+ channels were largely responsible. Sarcolemma voltage-gated Ca2+ currents were not activated following store depletion. Removal of external Ca2+ or the addition of the Ca2+ channel blocker nimodipine (1 microM) inhibited store refilling, as assessed by the magnitude of InsP3-evoked Ca2+ transients, with little or no change in bulk average cytoplasmic Ca2+ concentration. One hypothesis for these results is that the store may refill from a high subsarcolemma Ca2+ gradient. Influx via channels, some of which are voltage gated and others which lack voltage gating, may permit the establishment of a subsarcolemma Ca2+ gradient. Store access to the gradient allows InsP3-evoked Ca2+ signalling to be maintained over a wide voltage range in colonic smooth muscle.
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Affiliation(s)
- J G McCarron
- Institute of Biomedical and Life Sciences, Neuroscience and Biomedical Systems, West Medical Building, University of Glasgow, Glasgow G12 8QQ, UK.
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158
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Camello-Almaraz C, Pariente JA, Salido G, Camello PJ. Differential involvement of vacuolar H(+)-ATPase in the refilling of thapsigargin- and agonist-mobilized Ca(2+) stores. Biochem Biophys Res Commun 2000; 271:311-7. [PMID: 10799293 DOI: 10.1006/bbrc.2000.2633] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Our objective was to evaluate the role of vacuolar H(+)-ATPase and proton gradients in the refilling of Ca(2+) stores in fura-2-loaded pancreatic acinar cells. Once depleted with a high level of ACh, the Ca(2+) stores were replenished with a Ca(2+)-containing solution. The degree of refilling was estimated with a second release in response to either ACh (ACh-releasable store) or thapsigargin (thapsigargin-releasable store), a specific inhibitor of the endoplasmic reticulum Ca(2+) pumps. Both the protonophore nigericin and folimycin, a specific inhibitor of the vacuolar H(+)-ATPase, reduced reuptake into the ACh-mobilized stores but not into the thapsigargin-releasable pools. These treatments effectively dissipated the subcellular pH gradients (revealed by confocal observation of the distribution of a marker for acidic compartments), and did not impair the [Ca(2+)](i) response to ACh in control cells. Our results indicate that thapsigargin and ACh release heterogeneous Ca(2+) stores which are differently operated by vacuolar proton ATPase.
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Affiliation(s)
- C Camello-Almaraz
- Department of Physiology, University of Extremadura, Cáceres, 10071, Spain
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159
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Ambudkar IS. Regulation of calcium in salivary gland secretion. CRITICAL REVIEWS IN ORAL BIOLOGY AND MEDICINE : AN OFFICIAL PUBLICATION OF THE AMERICAN ASSOCIATION OF ORAL BIOLOGISTS 2000; 11:4-25. [PMID: 10682899 DOI: 10.1177/10454411000110010301] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Neurotransmitter-regulation of fluid secretion in the salivary glands is achieved by a coordinated sequence of intracellular signaling events, including the activation of membrane receptors, generation of the intracellular second messenger, inositol 1,4,5, trisphosphate, internal Ca2+ release, and Ca2+ influx. The resulting increase in cytosolic [Ca2+] ([Ca2+]i) regulates a number of ion transporters, e.g., Ca2+-activated K+ channel, Na+/K+/2Cl- co-transporter in the basolateral membrane, and the Ca2+-activated Cl- channel in the luminal membrane, which are intricately involved in fluid secretion. Thus, regulation of [Ca2+]i is central to the regulation of salivary acinar cell function and is achieved by the concerted activities of several ion channels and Ca2+-pumps localized in various cellular membranes. Ca2+ pumps, present in the endoplasmic reticulum and the plasma membrane, serve to remove Ca2+ from the cytosol. Ca2+ channels present in the endoplasmic reticulum and the plasma membrane facilitate rapid influx of Ca2+ into the cytosol from the internal Ca2+ stores and from the external medium, respectively. It is well-established that prolonged fluid secretion is regulated via a sustained elevation in [Ca2+]i that is primarily achieved by the influx of Ca2+ into the cell from the external medium. This Ca2+ influx occurs via a putative plasma-membrane-store-operated Ca2+ channel which has not yet been identified in any non-excitable cell type. Understanding the molecular nature of this Ca2+ influx mechanism is critical to our understanding of Ca2+ signaling in salivary gland cells. This review focuses on the various active and passive Ca2+ transport mechanisms in salivary gland cells--their localization, regulation, and role in neurotransmitter-regulation of fluid secretion. In addition to a historical perspective of Ca2+ signaling, recent findings and challenging problems facing this field are highlighted.
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Affiliation(s)
- I S Ambudkar
- Secretory Physiology Section, Gene Therapy and Therapeutics Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, Maryland 20892, USA
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160
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Glitsch MD, Parekh AB. Ca2+ store dynamics determines the pattern of activation of the store-operated Ca2+ current I(CRAC) in response to InsP3 in rat basophilic leukaemia cells. J Physiol 2000; 523 Pt 2:283-90. [PMID: 10699074 PMCID: PMC2269810 DOI: 10.1111/j.1469-7793.2000.t01-2-00283.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
1. The relationship between the amplitude of the store-operated Ca2+ ICR AC and intracellular inositol 1,4,5-triphosphate (InsP3) concentration is complex. In rat basophilic leukaemia (RBL-1) cells dialysed with high intracellular Ca2+ buffer, the relationship is supra-linear with a Hill coefficient of 12 and resembles an apparent 'all-or-none' phenomenon. The non-linearity seems to arise from InsP3 metabolism. However, it is not clear which InsP3-metabolising pathway engenders the non-linear behaviour nor whether ICRAC is always activated to its maximal extent by InsP3. 2. Using the whole-cell patch clamp technique, we dialysed RBL-1 cells with different concentrations of the InsP3 analogue InsP3-F. InsP3-F is broken down by Ins(1,4,5)P3 5-phosphatase but is not a substrate for Ins(1,4,5)P3 3-kinase. The relationship between InsP3-F and ICRAC amplitude was supra-linear and very similar to that with InsP3 but was distinct from the graded relationship seen with the non-metabolisable analogue Ins2,4,5P3. 3. In the presence of high intracellular Ca2+ buffer, InsP3-F activated ICRAC to its maximal extent. With moderate Ca2+ buffer, however, sub-maximal ICRAC could be obtained to a maximal InsP3-F concentration. Nevertheless, the relationship between the amplitude of ICRAC and InsP3-F concentration was still supra-linear. 4. Submaximal ICRAC in response to InsP3-F in the presence of moderate Ca2+ buffer was due to partial depletion of the stores, because the size of the current could be increased by thapsigargin. 5. The data suggest that first Ins(1,4,5)P3 5-phosphatase is an important factor which contributes to the non-linear relationship between InsP3 concentration and the amplitude of ICRAC and second, InsP3 does not always activate ICRAC to its maximal extent. At moderate buffer strengths, submaximal ICRAC is evoked by maximal InsP3. However, the supra-linear relationship between InsP3 concentration and amplitude of the current still holds.
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MESH Headings
- Animals
- Calcium/metabolism
- Calcium/pharmacology
- Calcium Channels/drug effects
- Calcium Channels/metabolism
- Calcium-Transporting ATPases/antagonists & inhibitors
- Calcium-Transporting ATPases/metabolism
- Chelating Agents/pharmacology
- Dialysis
- Disulfiram/pharmacology
- Dose-Response Relationship, Drug
- Egtazic Acid/analogs & derivatives
- Egtazic Acid/metabolism
- Egtazic Acid/pharmacology
- Enzyme Inhibitors/pharmacology
- Inositol 1,4,5-Trisphosphate/analogs & derivatives
- Inositol 1,4,5-Trisphosphate/metabolism
- Inositol 1,4,5-Trisphosphate/pharmacology
- Inositol Polyphosphate 5-Phosphatases
- Intracellular Fluid/metabolism
- Ion Transport/drug effects
- Leukemia, Basophilic, Acute/metabolism
- Leukemia, Basophilic, Acute/pathology
- Membrane Potentials/drug effects
- Patch-Clamp Techniques
- Phosphoric Monoester Hydrolases/antagonists & inhibitors
- Phosphoric Monoester Hydrolases/metabolism
- Rats
- Signal Transduction/drug effects
- Substrate Specificity
- Tumor Cells, Cultured
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Affiliation(s)
- M D Glitsch
- Department of Physiology, University of Oxford, Parks Road, Oxford OX1 3PT, UK
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161
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Fierro L, Parekh AB. Substantial depletion of the intracellular Ca2+ stores is required for macroscopic activation of the Ca2+ release-activated Ca2+ current in rat basophilic leukaemia cells. J Physiol 2000; 522 Pt 2:247-57. [PMID: 10639101 PMCID: PMC2269755 DOI: 10.1111/j.1469-7793.2000.t01-1-00247.x] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
1. Tight-seal whole-cell patch clamp experiments were performed to examine the ability of different intracellular Ca2+ mobilising agents to activate the Ca2+ release-activated Ca2+ current (ICRAC) in rat basophilic leukaemia (RBL-1) cells under conditions of weak cytoplasmic Ca2+ buffering. 2. Dialysis with a maximal concentration of inositol 1,4,5-trisphosphate (IP3) routinely failed to activate macroscopic ICRAC in low buffer (0.mM EGTA, BAPTA or dimethyl BAPTA), whereas it activated the current to its maximal extent in high buffer (10 mM EGTA). Dialysis with a poorly metabolisable analogue of IP3, with ionomycin, or with IP3 and ionomycin all failed to generate macroscopic ICRAC in low Ca2+ buffering conditions. 3. Dialysis with the sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) pump blocker thapsigargin was able to activate ICRAC even in the presence of low cytoplasmic Ca2+ buffering, albeit at a slow rate. Exposure to IP3 together with the SERCA blockers thapsigargin, thapsigargicin or cyclopiazonic acid rapidly activated ICRAC in low buffer. 4. Following activation of ICRAC by intracellular dialysis with IP3 and thapsigargin in low buffer, the current was very selective for Ca2+ (apparent KD of 1 mM) Sr2+ and Ba2+ were less effective charge carriers and Na+ was not conducted to any appreciable extent. The ionic selectivity of ICRAC was very similar in low or high intracellular Ca2+ buffer. 5. Fast Ca2+-dependent inactivation of ICRAC occurred at a similar rate and to a similar extent in low or high Ca2+ buffer. Ca2+-dependent inactivation is not the reason why macroscopic ICRAC cannot be seen under conditions of low cytoplasmic Ca2+ buffering. 6. ICRAC could be activated by combining IP3 with thapsigargin, even in the presence of 100 microM Ca2+ and the absence of any exogenous Ca2+ chelator, where ATP and glutamate represented the only Ca2+ buffers in the pipette solution. 7. Our results suggest that a threshold exists within the IP3-sensitive Ca2+ store, below which intraluminal Ca2+ needs to fall before ICRAC activates. Possible models to explain the results are discussed.
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Affiliation(s)
- L Fierro
- Laboratory of Molecular and Cellular Signalling, Department of Physiology, University of Oxford, Parks Road, Oxford OX1 3PT, UK
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162
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Tengholm A, Hellman B, Gylfe E. Glucose regulation of free Ca(2+) in the endoplasmic reticulum of mouse pancreatic beta cells. J Biol Chem 1999; 274:36883-90. [PMID: 10601240 DOI: 10.1074/jbc.274.52.36883] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Free Ca(2+) was measured in organelles of individual mouse pancreatic beta cells loaded with the low affinity indicator furaptra. After removal of cytoplasmic indicator by controlled digitonin permeabilization the organelle Ca(2+) was located essentially in the endoplasmic reticulum (ER), >90% being sensitive to inhibition of sarco(endo)plasmic reticulum Ca(2+)-ATPases. The Ca(2+) accumulation in the ER of intact beta cells depended in a hyperbolic fashion on the glucose concentration with half-maximal and maximal filling at 5.5 and >20 mM, respectively. Also elevation of cytoplasmic Ca(2+) by K(+) depolarization significantly enhanced the Ca(2+) accumulation. In permeabilized beta cells 1-3 mM ATP caused rapid Ca(2+) filling of the ER reaching almost 500 microM. At 50 nM, Ca(2+) ER became half-maximally filled at 45 microM ATP, whereas only 3.5 microM ATP was required at 200 nM Ca(2+). Inositol 1,4,5-trisphosphate induced a rapid release of about 65% of the ER Ca(2+), and its precursor phosphatidylinositol 4,5-bisphosphate was found to slowly mobilize 75% by another mechanism. It is concluded that glucose is an efficient stimulator of Ca(2+) uptake in the ER of pancreatic beta cells both by increasing ATP and cytoplasmic Ca(2+). Because physiological concentrations of cytoplasmic ATP are in the mM range, Ca(2+) sequestration can be anticipated to be modulated by factors reducing its ATP sensitivity.
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Affiliation(s)
- A Tengholm
- Department of Medical Cell Biology, Uppsala University, SE-751 23 Uppsala, Sweden
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163
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Krause E, Schmid A, González A, Schulz I. Low cytoplasmic [Ca(2+)] activates I(CRAC) independently of global Ca(2+) store depletion in RBL-1 cells. J Biol Chem 1999; 274:36957-62. [PMID: 10601250 DOI: 10.1074/jbc.274.52.36957] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Release of Ca(2+) from inositol (1,4,5)-trisphosphate-sensitive Ca(2+) stores causes "capacitative calcium entry," which is mediated by the so-called "Ca(2+) release-activated Ca(2+) current" (I(CRAC)) in RBL-1 cells. Refilling of the Ca(2+) stores or high cytoplasmic [Ca(2+)] ([Ca(2+)](cyt)) inactivate I(CRAC). Here we address the question if also [Ca(2+)](cyt) lower than the resting [Ca(2+)](cyt) influences store-operated channels. We therefore combined patch clamp and mag fura-2 fluorescence methods to determine simultaneously both I(CRAC) and [Ca(2+)] within Ca(2+) stores of RBL-1 cells ([Ca(2+)](store)). We found that low [Ca(2+)](cyt) in the range of 30-50 nM activates I(CRAC) and Ca(2+) influx spontaneously and independently of global Ca(2+) store depletion, while elevation of [Ca(2+)](cyt) to the resting [Ca(2+)](cyt) (100 nM) resulted in store dependence of I(CRAC) activation. We conclude that spontaneous activation of I(CRAC) by low [Ca(2+)](cyt) could serve as a feedback mechanism keeping the resting [Ca(2+)](cyt) constant.
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Affiliation(s)
- E Krause
- 2. Physiologisches Institut, Universität des Saarlandes, D-66421 Homburg/Saar, Germany
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164
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Chen YJ, Lin JK, Lin-Shiau SY. Proliferation arrest and induction of CDK inhibitors p21 and p27 by depleting the calcium store in cultured C6 glioma cells. Eur J Cell Biol 1999; 78:824-31. [PMID: 10604659 DOI: 10.1016/s0171-9335(99)80033-8] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022] Open
Abstract
C6 glioma - Ca2+ depletion - proliferation arrest morphology change - CDK inhibitor In this study, we investigated the role of the intracellular calcium store in modulating the cellular proliferation and the expression of cell cycle regulatory proteins in cultured C6 glioma cells. By means of microspectrofluorimetry and Ca(2+)-sensitive indicator fura-2, we found that the intracellular Ca2+ pump inhibitors, thapsigargin (TG) irreversibly and 2,5-ditert-butyl-hydroquinone (DBHQ) reversibly depleted the Ca(2+)-store accompanied with the induction of G0/G1 arrest, an increase in glial fibrillary acidic protein (GFAP) expression and morphological changes from a round flat shape to a differentiated spindle-shaped cell. The machinery underlying these changes induced by Ca(2+)-store depletion was investigated. The results indicated that Ca(2+)-store depletion caused an increased expression of p21 and p27 proteins (cyclin-dependent kinase inhibitors), with unchanged mutant p53 protein of C6 cells but reduced amounts of the cell cycle regulators: cyclin-dependent kinase 2 (CDK2), cdc2, cyclin C, cyclin D1, cyclin D3 and proliferating cell nuclear antigen (PCNA) in a time-dependent manner. These findings indicate a new function of the endoplasmic reticulum (ER) Ca2+ store in regulating cellular proliferation rate through altering the expression of p21 and p27 proteins. Moreover, cellular differentiation as revealed by spindle-shaped morphology and induced GFAP expression were also modulated by the ER Ca2+ store. The implication of this finding is that the abnormal growth of cancer cells such as C6 glioma cells may be derived from a signalling of the ER which can be manipulated by depleting the Ca2+ store.
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Affiliation(s)
- Y J Chen
- Institute of Toxicology, College of Medicine, National Taiwan University, Taipei
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165
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Fierro L, Parekh AB. On the characterisation of the mechanism underlying passive activation of the Ca2+ release-activated Ca2+ current ICRAC in rat basophilic leukaemia cells. J Physiol 1999; 520 Pt 2:407-16. [PMID: 10523410 PMCID: PMC2269586 DOI: 10.1111/j.1469-7793.1999.00407.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
1. Tight-seal whole-cell patch clamp experiments were performed to investigate the mechanism whereby passive depletion of stores activates the Ca2+ release-activated Ca2+ current (ICRAC) in rat basophilic leukaemia (RBL) cells. 2. Passive depletion of stores was achieved by dialysing cells with different concentrations of Ca2+ chelators. Low concentrations generally evoked a submaximal ICRAC, which developed slowly and monophasically. Higher concentrations resulted in a biphasic current in which the initial slow monophasic component developed into a faster and bigger second phase. 3. The kinetics of ICRAC as well as its final amplitude were not affected by Ca2+ chelators that had different affinities or speeds of binding. 4. Exogenous Ca2+ binding ratios > or = 16,670 were necessary to fully activate ICRAC. Because the Ca2+ binding ratio within the stores is presumably low, this indicates that other factors like Ca2+ transport across the stores membrane are rate limiting for passive store depletion. 5. Heparin and Ruthenium Red both failed to affect passive Ca2+ leak from the intracellular stores. 6. Treatment with sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) pump blockers dramatically altered the kinetics of activation of biphasic currents, and increased the amplitude of monophasic ones. 7. Our results suggest that SERCA pumps are very effective in preventing ICRAC from activating passively, and are responsible for the phasic nature of the current, its time course of development and its overall extent.
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Affiliation(s)
- L Fierro
- Laboratory of Molecular and Cellular Signalling, Department of Physiology, University of Oxford, Parks Road, Oxford OX1 3PT, UK
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166
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Kidd JF, Fogarty KE, Tuft RA, Thorn P. The role of Ca2+ feedback in shaping InsP3-evoked Ca2+ signals in mouse pancreatic acinar cells. J Physiol 1999; 520 Pt 1:187-201. [PMID: 10517811 PMCID: PMC2269552 DOI: 10.1111/j.1469-7793.1999.00187.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
1. Cytosolic Ca2+ has been proposed to act as both a positive and a negative feedback signal on the inositol trisphosphate (InsP3) receptor. However, it is unclear how this might affect the Ca2+ response in vivo. 2. Mouse pancreatic acinar cells were whole-cell patch clamped to record the Ca2+-dependent chloride (Cl(Ca)) current spikes and imaged to record the cytosolic Ca2+ spikes elicited by the injection of Ins(2,4,5)P3. Increasing concentrations of Ca2+ buffer (up to 200 microM EGTA or BAPTA) were associated with the appearance of steps in the current activation phase and a prevalence of smaller-amplitude Cl(Ca) spikes. Imaging experiments showed that with increased buffer the secretory pole cytosolic Ca2+ signal became fragmented and spatially discrete Ca2+ release events were observed. 3. At higher buffer concentrations (200-500 microM), increasing concentrations of EGTA increased spike frequency and reduced spike amplitude. In contrast, BAPTA decreased spike frequency and maintained large spike amplitudes. 4. We conclude that, during InsP3-evoked spiking, long-range Ca2+ feedback ( approximately 2-4 microm) shapes the rising phase of the Ca2+ signal by acting to co-ordinate discrete Ca2+ release events and short-range ( approximately 40 nm) Ca2+ feedback acts to inhibit further Ca2+ release.
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Affiliation(s)
- J F Kidd
- The Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QJ, UK
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167
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Abstract
The concentration of free calcium ions (Ca(2+)) in the cytosol is precisely regulated and can be rapidly increased in response to various types of stimuli. Since Ca(2+) can be used to control different processes in the same cell, the spatial organization of cytosolic Ca(2+) signals is of considerable importance. Polarized cells have advantages for Ca(2+) studies since localized signals can be related to particular organelles. The pancreatic acinar cell is well-characterized with a clearly polarized structure and function. Since the discovery of the intracellular Ca(2+)-releasing function of inositol 1,4,5-trisphosphate (IP(3)) in the pancreas in the early 1980s, this cell has become a popular study object and is now one of the best-characterized with regard to Ca(2+) signaling properties. Stimulation of pancreatic acinar cells with the neurotransmitter acetylcholine or the hormone cholecystokinin evokes Ca(2+) signals that are either local or global, depending on the agonist concentration and the length of the stimulation period. The nature of the Ca(2+) transport events across the basal and apical plasma membranes as well as the involvement of the endoplasmic reticulum (ER), the nucleus, the mitochondria, and the secretory granules in Ca(2+) signal generation and termination have become much clearer in recent years.
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Affiliation(s)
- O H Petersen
- MRC Secretory Control Research Group, The Physiological Laboratory, University of Liverpool, Liverpool, UK.
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168
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Abstract
The intracellular mechanisms regulating pancreatic acinar cell function are more complex than previously realized. This is probably due in part to the need to match the biosynthetic and secretory functions of the cells. Much information is available on how secretagogue receptors acutely couple through heterotrimeric G proteins to increase intracellular messengers, particularly cytoplasmic free Ca(2+), although details are still being worked out. Less is known about how Ca(2+) signals to induce fusion of zymogen granules with the apical plasma membrane. Investigation has focused on the proteins of the zymogen granule membrane, and several novel proteins have recently been identified. In addition, understanding of the three MAP kinase cascades, the mTOR-p70S6 kinase pathway, and the focal adhesion kinase pathway in acinar cells is increasing. The functions of these pathways in acini have been linked to mitogenesis, protein synthesis, and regulation of the cytoskeleton.
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Affiliation(s)
- J A Williams
- Departments of Physiology and Internal Medicine, University of Michigan, Ann Arbor, Michigan 48109, USA.
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169
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Abstract
The field of subcellular Ca2+ homeostasis is evolving rapidly. In parallel with improvements in spatial and temporal resolution of Ca2+ imaging techniques, new methods using the natural cell machinery to target Ca2+-sensitive proteins such as aequorin to precise intracellular locations promise superb specificity to measure [Ca2+] in defined subcellular environments.
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Affiliation(s)
- Javier Alvarez
- J. Alvarez, M. Montero and J. García-Sancho are in the Instituto de Biología y Genética Molecular (IBGM), Departamento de Fisiología y Bioquímica, Facultad de Medicina, Universidad de Valladolid y Consejo Superior de Investigaciones Científicas, 47005-Valladolid, Spain
| | - Mayte Montero
- J. Alvarez, M. Montero and J. García-Sancho are in the Instituto de Biología y Genética Molecular (IBGM), Departamento de Fisiología y Bioquímica, Facultad de Medicina, Universidad de Valladolid y Consejo Superior de Investigaciones Científicas, 47005-Valladolid, Spain
| | - Javier García-Sancho
- J. Alvarez, M. Montero and J. García-Sancho are in the Instituto de Biología y Genética Molecular (IBGM), Departamento de Fisiología y Bioquímica, Facultad de Medicina, Universidad de Valladolid y Consejo Superior de Investigaciones Científicas, 47005-Valladolid, Spain
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170
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Gilon P, Arredouani A, Gailly P, Gromada J, Henquin JC. Uptake and release of Ca2+ by the endoplasmic reticulum contribute to the oscillations of the cytosolic Ca2+ concentration triggered by Ca2+ influx in the electrically excitable pancreatic B-cell. J Biol Chem 1999; 274:20197-205. [PMID: 10400636 DOI: 10.1074/jbc.274.29.20197] [Citation(s) in RCA: 108] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The role of intracellular Ca2+ pools in oscillations of the cytosolic Ca2+ concentration ([Ca2+]c) triggered by Ca2+ influx was investigated in mouse pancreatic B-cells. [Ca2+]c oscillations occurring spontaneously during glucose stimulation or repetitively induced by pulses of high K+ (in the presence of diazoxide) were characterized by a descending phase in two components. A rapid decrease in [Ca2+]c coincided with closure of voltage-dependent Ca2+ channels and was followed by a slower phase independent of Ca2+ influx. Blocking the SERCA pump with thapsigargin or cyclopiazonic acid accelerated the rising phase of [Ca2+]c oscillations and increased their amplitude, which suggests that the endoplasmic reticulum (ER) rapidly takes up Ca2+. It also suppressed the slow [Ca2+]c recovery phase, which indicates that this phase corresponds to the slow release of Ca2+ that was taken up by the ER during the upstroke of the [Ca2+]c transient. Glucose promoted the buffering capacity of the ER and amplified the slow [Ca2+]c recovery phase. The slow phase induced by high K+ pulses was not affected by modulators of Ca2+- or inositol 1,4,5-trisphosphate-induced Ca2+ release, did not involve a depolarization-induced Ca2+ release, and was also observed at the end of a rapid rise in [Ca2+]c triggered from caged Ca2+. It is attributed to passive leakage of Ca2+ from the ER. We suggest that the ER displays oscillations of the Ca2+ concentration ([Ca2+]ER) concomitant and parallel to [Ca2+]c. The observation that thapsigargin depolarizes the membrane of B-cells supports the proposal that the degree of Ca2+ filling of the ER modulates the membrane potential. Therefore, [Ca2+]ER oscillations occurring during glucose stimulation are likely to influence the bursting behavior of B-cells and eventually [Ca2+]c oscillations.
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Affiliation(s)
- P Gilon
- Unité d'Endocrinologie et Métabolisme, University of Louvain Faculty of Medicine, Av. Hippocrate 55, 1200 Brussels, Belgium.
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171
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Mogami H, Gardner J, Gerasimenko OV, Camello P, Petersen OH, Tepikin AV. Calcium binding capacity of the cytosol and endoplasmic reticulum of mouse pancreatic acinar cells. J Physiol 1999; 518 ( Pt 2):463-7. [PMID: 10381592 PMCID: PMC2269443 DOI: 10.1111/j.1469-7793.1999.0463p.x] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
1. The droplet technique was used in this study to measure total calcium loss from pancreatic acinar cells due to calcium extrusion. The calcium binding capacity of the cytosol (kc) was measured as the ratio of the decrease in the total calcium concentration of the cytosol of the cell (Delta[Ca]c) and the synchronously occurring decrease in the free calcium ion concentration in the cytosol (Delta[Ca2+]c). The calcium dependency of the calcium binding capacity was determined by plotting values of kc against the corresponding [Ca2+]c. The rise in the cytosolic Ca2+ concentration of pancreatic acinar cells was triggered by stimulation with a supramaximal dose of cholecystokinin (CCK). The recovery of [Ca2+]c during continued exposure to the agonist was due to calcium extrusion from the cell. 2. The calcium binding capacity was about 1500-2000 for the [Ca2+]c range 150-500 nM. The mechanism of buffering was not investigated in this study. The calcium binding capacity of the cytosol did not vary significantly with [Ca2+]c in this range. The CCK-evoked decrease in the total calcium concentration in the lumen of the endoplasmic reticulum (ER) can be estimated from our data, taking into account previously published values for the volume of the ER in pancreatic acinar cells. Comparing the decrease in the total ER calcium concentration with our recently reported values for agonist-induced reductions in the free Ca2+ concentration inside the ER, we estimate that the calcium binding capacity of the ER is approximately 20. In pancreatic acinar cells we have therefore found a difference of two orders of magnitude in the efficiency of calcium buffering in the cytosol and the ER lumen.
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Affiliation(s)
- H Mogami
- The Medical Research Council Secretory Control Research Group, The Physiological Laboratory, University of Liverpool, Liverpool L69 3BX, UK
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172
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Maechler P, Kennedy ED, Sebö E, Valeva A, Pozzan T, Wollheim CB. Secretagogues modulate the calcium concentration in the endoplasmic reticulum of insulin-secreting cells. Studies in aequorin-expressing intact and permeabilized ins-1 cells. J Biol Chem 1999; 274:12583-92. [PMID: 10212237 DOI: 10.1074/jbc.274.18.12583] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The precise regulation of the Ca2+ concentration in the endoplasmic reticulum ([Ca2+]er) is important for protein processing and signal transduction. In the pancreatic beta-cell, dysregulation of [Ca2+]er may cause impaired insulin secretion. The Ca2+-sensitive photoprotein aequorin mutated to lower its Ca2+ affinity was stably expressed in the endoplasmic reticulum (ER) of rat insulinoma INS-1 cells. The steady state [Ca2+]er was 267 +/- 9 microM. Both the Ca2+-ATPase inhibitor cyclopiazonic acid and 4-chloro-m-cresol, an activator of ryanodine receptors, caused an almost complete emptying of ER Ca2+. The inositol 1,4,5-trisphosphate generating agonists, carbachol, and ATP, reduced [Ca2+]er by 20-25%. Insulin secretagogues that raise cytosolic [Ca2+] by membrane depolarization increased [Ca2+]er in the potency order K+ >> glucose > leucine, paralleling their actions in the cytosolic compartment. Glucose, which augmented [Ca2+]er by about 25%, potentiated the Ca2+-mobilizing effect of carbachol, explaining the corresponding observation in cytosolic [Ca2+]. The filling of ER Ca2+ by glucose is not directly mediated by ATP production as shown by the continuous monitoring of cytosolic ATP in luciferase expressing cells. Both glucose and K+ increase [Ca2+]er, but only the former generated whereas the latter consumed ATP. Nonetheless, drastic lowering of cellular ATP with a mitochondrial uncoupler resulted in a marked decrease in [Ca2+]er, emphasizing the requirement for mitochondrially derived ATP above a critical threshold concentration. Using alpha-toxin permeabilized cells in the presence of ATP, glucose 6-phosphate did not change [Ca2+]er, invalidating the hypothesis that glucose acts through this metabolite. Therefore, insulin secretagogues that primarily stimulate Ca2+ influx, elevate [Ca2+]er to ensure beta-cell homeostasis.
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Affiliation(s)
- P Maechler
- Division of Clinical Biochemistry and Experimental Diabetology, Department of Internal Medicine, University Medical Center, CH-1211 Geneva 4, Switzerland
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173
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Craske M, Takeo T, Gerasimenko O, Vaillant C, Török K, Petersen OH, Tepikin AV. Hormone-induced secretory and nuclear translocation of calmodulin: oscillations of calmodulin concentration with the nucleus as an integrator. Proc Natl Acad Sci U S A 1999; 96:4426-31. [PMID: 10200278 PMCID: PMC16348 DOI: 10.1073/pnas.96.8.4426] [Citation(s) in RCA: 71] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Many important enzyme activities are regulated by Ca2+-dependent interactions with calmodulin (CaM). Some of the most important targets for CaM action are in the nucleus, and Ca2+-dependent CaM translocation into this organelle has been reported. Hormone-evoked cytosolic Ca2+ signals occur physiologically as oscillations, but, so far, oscillations in CaM concentration have not been described. We loaded fluorescent-labeled CaM into pancreatic acinar cells and monitored the fluorescence in various regions by confocal microscopy. Sustained high concentrations of the hormone cholecystokinin or the neurotransmitter acetylcholine evoked a transient movement of cytosolic CaM from the basal nonnuclear area into the secretory granule region and, thereafter, a more substantial and prolonged translocation of CaM into the nucleoplasm. About 50% of the CaM that bound Ca2+ translocated. At a lower hormone concentration, evoking Ca2+ oscillations, regular spikes of increased CaM concentration were seen in the secretory granule region with mirror image spikes of decreased CaM concentration in the basal nonnuclear region. The nucleus was able to integrate the Ca2+ spike-evoked pulses of CaM translocation into a sustained elevation of the nucleoplasmic concentration of this protein.
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Affiliation(s)
- M Craske
- Medical Research Council Secretory Control Research Group, Physiological Laboratory, University of Liverpool, Liverpool L69 3BX, United Kingdom
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174
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Petersen OH, Burdakov D, Tepikin AV. Regulation of store-operated calcium entry: lessons from a polarized cell. Eur J Cell Biol 1999; 78:221-3. [PMID: 10350209 DOI: 10.1016/s0171-9335(99)80054-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Affiliation(s)
- O H Petersen
- MRC Secretory Control Research Group, The Physiological Laboratory, University of Liverpool, UK.
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175
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Affiliation(s)
- D Sanders
- Plant Laboratory, Biology Department, University of York, York YO1 5YW, United Kingdom
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176
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Barritt GJ. Receptor-activated Ca2+ inflow in animal cells: a variety of pathways tailored to meet different intracellular Ca2+ signalling requirements. Biochem J 1999; 337 ( Pt 2):153-69. [PMID: 9882611 PMCID: PMC1219948] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/09/2023]
Abstract
Receptor-activated Ca2+ channels (RACCs) play a central role in regulation of the functions of animal cells. Together with voltage-operated Ca2+ channels (VOCCs) and ligand-gated non-selective cation channels, RACCs provide a variety of pathways by which Ca2+ can be delivered to the cytoplasmic space and the endoplasmic reticulum (ER) in order to initiate or maintain specific types of intracellular Ca2+ signal. Store-operated Ca2+ channels (SOCs), which are activated by a decrease in Ca2+ in the ER, are a major subfamily of RACCs. A careful analysis of the available data is required in order to discern the different types of RACCs (differentiated chiefly on the basis of ion selectivity and mechanism of activation) and to properly develop hypotheses for structures and mechanisms of activation. Despite much intensive research, the structures and mechanisms of activation of RACCs are only now beginning to be understood. In considering the physiological functions of the different RACCs, it is useful to consider the specificity for Ca2+ of each type of cation channel and the rate at which Ca2+ flows through a single open channel; the locations of the channels on the plasma membrane (in relation to the ER, cytoskeleton and other intracellular units of structure and function); the Ca2+-responsive enzymes and proteins; and the intracellular buffers and proteins that control the distribution of Ca2+ in the cytoplasmic space. RACCs which are non-selective cation channels can deliver Ca2+ directly to specific regions of the cytoplasmic space, and can also admit Na+, which induces depolarization of the plasma membrane, the opening of VOCCs and the subsequent inflow of Ca2+. SOCs appear to deliver Ca2+ specifically to the ER, thereby maintaining oscillating Ca2+ signals.
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Affiliation(s)
- G J Barritt
- Department of Medical Biochemistry, School of Medicine, Faculty of Health Sciences, Flinders University, G.P.O. Box 2100, Adelaide, South Australia 5001, Australia.
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177
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Liu X, O'Connell A, Ambudkar IS. Ca2+-dependent inactivation of a store-operated Ca2+ current in human submandibular gland cells. Role of a staurosporine-sensitive protein kinase and the intracellular Ca2+ pump. J Biol Chem 1998; 273:33295-304. [PMID: 9837902 DOI: 10.1074/jbc.273.50.33295] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Stimulation of human submandibular gland cells with carbachol, inositol trisphosphate (IP3), thapsigargin, or tert-butylhydroxyquinone induced an inward current that was sensitive to external Ca2+ concentration ([Ca2+]e) and was also carried by external Na+ or Ba2+ (in a Ca2+-free medium) with amplitudes in the order Ca2+ > Ba2+ > Na+. All cation currents were blocked by La3+ and Gd3+ but not by Zn2+. The IP3-stimulated current with 10 microM 3-deoxy-3-fluoro-D-myo-inositol 1,4,5-triphosphate and 10 mM 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid in the pipette solution, showed 50% inactivation in <5 min and >5 min with 10 and 1 mM [Ca2+]e, respectively. The Na+ current was not inactivated, whereas the Ba2+ current inactivated at a slower rate. The protein kinase inhibitor, staurosporine, delayed the inactivation and increased the amplitude of the current, whereas the protein Ser/Thr phosphatase inhibitor, calyculin A, reduced the current. Thapsigargin- and tert-butylhydroxyquinone-stimulated Ca2+ currents inactivated faster. Importantly, these agents accelerated the inactivation of the IP3-stimulated current. The data demonstrate that internal Ca2+ store depletion-activated Ca2+ current (ISOC) in this salivary cell line is regulated by a Ca2+-dependent feedback mechanism involving a staurosporine-sensitive protein kinase and the intracellular Ca2+ pump. We suggest that the Ca2+ pump modulates ISOC by regulating [Ca2+]i in the region of Ca2+ influx.
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Affiliation(s)
- X Liu
- Secretory Physiology Section, Gene Therapy and Therapeutics Branch, NIDR, National Institutes of Health, Bethesda, Maryland 20892, USA
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178
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Morgan AJ, Jacob R. Differential modulation of the phases of a Ca2+ spike by the store Ca2+-ATPase in human umbilical vein endothelial cells. J Physiol 1998; 513 ( Pt 1):83-101. [PMID: 9782161 PMCID: PMC2231278 DOI: 10.1111/j.1469-7793.1998.083by.x] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
1. Histamine-stimulated cytosolic free Ca2+ ([Ca2+]i) oscillations in human umbilical vein endothelial cells (HUVECs) comprise repetitive spikes generated by pulsatile release from stores. We have investigated the roles of the store Ca2+-ATPases in regulating both the upstroke and downstroke of a Ca2+ spike. 2. The sarco-endoplasmic reticulum Ca2+-ATPase (SERCA) inhibitor cyclopiazonic acid (CPA) dramatically affected oscillations whereas inhibition of the plasma membrane Ca2+-ATPase (PMCA) with La3+ had little effect. This and other evidence suggested that the downstroke of a spike is predominantly mediated by SERCA. 3. Artificial [Ca2+]i spiking generated by repetitive pulsatile application of 0.3 microM histamine in Ca2+-free medium did not cause net loss of Ca2+ from the cell whereas repetitive pulsatile application of 1 and 10 microM histamine did, with the higher concentration being more effective. We conclude that there is an inverse relationship between stimulus intensity and relative SERCA activity. 4. For a Ca2+ transient, the initiation of release was suppressed by SERCA during either the lag phase or the interspike period (ISP) since: (i) the ISP was shortened by low CPA concentrations, (ii) higher concentrations of CPA stimulated an explosive Ca2+ release when applied during the ISP but not when applied in the absence of agonist, and (iii) CPA synchronized the initial Ca2+ response to a low histamine dose (even recruiting silent, histamine-unresponsive cells). 5. Two aspects of the regenerative upstroke of a spike were differently affected by SERCA inhibition: Ca2+ wave velocity was entirely unaffected by CPA whereas the local rate of rise was increased. 6. The [Ca2+]i at which a Ca2+ spike terminated depended on SERCA since CPA dose dependently enhanced the peak [Ca2+]i. 7. We conclude that SERCA plays a powerful and dynamic role in regulating [Ca2+]i oscillations in HUVECs. SERCA differentially modulates the phases of Ca2+ release in addition to bringing about the falling phase of a Ca2+ spike.
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Affiliation(s)
- A J Morgan
- Vascular Biology Research Centre, Physiology Group, Biomedical Sciences Division, King's College London, London W8 7AH, UK.
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179
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Abstract
Neuronal calcium stores associated with specialized intracellular organelles, such as endoplasmic reticulum and mitochondria, dynamically participate in generation of cytoplasmic calcium signals which accompany neuronal activity. They fulfil a dual role in neuronal Ca2+ homeostasis being involved in both buffering the excess of Ca2+ entering the cytoplasm through plasmalemmal channels and providing an intracellular source for Ca2+. Increase of Ca2+ content within the stores regulates the availability and magnitude of intracellular calcium release, thereby providing a mechanism which couples the neuronal activity with functional state of intracellular Ca2+ stores. Apart of 'classical' calcium stores (endoplasmic reticulum and mitochondria) other organelles (e.g. nuclear envelope and neurotransmitter vesicles) may potentially act as a functional Ca2+ storage compartments. Calcium ions released from internal stores participate in many neuronal functions, and might be primarily involved in regulation of various aspects of neuronal plasticity.
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Affiliation(s)
- A J Verkhratsky
- Max Delbrück Center for Molecular Medicine, Berlin, Germany.
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180
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Liu X, Rojas E, Ambudkar IS. Regulation of KCa current by store-operated Ca2+ influx depends on internal Ca2+ release in HSG cells. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 275:C571-80. [PMID: 9688612 DOI: 10.1152/ajpcell.1998.275.2.c571] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
This study examines the Ca2+ influx-dependent regulation of the Ca2+-activated K+ channel (KCa) in human submandibular gland (HSG) cells. Carbachol (CCh) induced sustained increases in the KCa current and cytosolic Ca2+ concentration ([Ca2+]i), which were prevented by loading cells with 1,2-bis(2-aminophenoxy)ethane-N,N,N', N'-tetraacetic acid (BAPTA). Removal of extracellular Ca2+ and addition of La3+ or Gd3+, but not Zn2+, inhibited the increases in KCa current and [Ca2+]i. Ca2+ influx during refill (i.e., addition of Ca2+ to cells treated with CCh and then atropine in Ca2+-free medium) failed to evoke increases in the KCa current but achieved internal Ca2+ store refill. When refill was prevented by thapsigargin, Ca2+ readdition induced rapid activation of KCa. These data provide further evidence that intracellular Ca2+ accumulation provides tight buffering of [Ca2+]i at the site of Ca2+ influx (H. Mogami, K. Nakano, A. V. Tepikin, and O. H. Petersen. Cell 88: 49-55, 1997). We suggest that the Ca2+ influx-dependent regulation of the sustained KCa current in CCh-stimulated HSG cells is mediated by the uptake of Ca2+ into the internal Ca2+ store and release via the inositol 1,4,5-trisphosphate-sensitive channel.
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Affiliation(s)
- X Liu
- Secretory Physiology Section, Gene Therapy and Therapeutics Branch, National Institute of Dental Research, National Institutes of Health, Bethesda, Maryland 20892, USA
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Lui PP, Kong SK, Kwok TT, Lee CY. The nucleus of HeLa cell contains tubular structures for Ca2+ signalling. Biochem Biophys Res Commun 1998; 247:88-93. [PMID: 9636660 DOI: 10.1006/bbrc.1998.8649] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
It has long been assumed that Ca2+ are translocated from the cytosol to the cell nucleus by a long distance to activate transcription machinery buried deep in the nucleoplasm. However, this model has been recently challenged. When HeLa cells were loaded with fluo-3, highly fluorescent spots of approximately 2 microns in diameter were observed in the cell nucleus while the fluo-3 signals were low in their neighbouring nucleoplasm as determined by confocal microscopy. These fluorescent spots were devoid of but usually associated with chromatin on their boundary. When cells were stimulated by ionomycin (1 microM), the fluo-3 fluorescence in these spots increased faster than that in their neighbouring nucleoplasm. In another experiment, optical sections with hot spot(s) were used to construct 3-D images to study the morphology of the hot spots. Views of reconstruction from different angles indicated that the hot spots formed a tubular structure with a connection to the nucleocytoplasmic interface. Moreover, injection of calcium green-dextran (70 kDa), a Ca(2+)-sensitive indicator conjugated with an inert molecule of large molecular size, into the cytosol leads to a formation of signals also in a tubular shape inside the nucleoplasm. This suggests that the 'channels' are real inside the nucleus and they are derived from an invagination of the double-membraned nuclear envelope. Taken together, our results indicate (1) tubular structures are found inside the cell nucleus; (2) they are extended from the cytosol into the nucleus through the invagination of the double membraned nuclear envelope; (3) molecules of molecular size up to 70 kDa could penetrate into these 'tunnels'; (4) Ca2+ can be released or transported into the cell nucleus through these tubular structures after ionomycin stimulation; and (5) the structures are usually associated with chromatin.
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Affiliation(s)
- P P Lui
- Department of Biochemistry, Chinese University of Hong Kong, Shatin
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Petersen OH, Gerasimenko OV, Gerasimenko JV, Mogami H, Tepikin AV. The calcium store in the nuclear envelope. Cell Calcium 1998; 23:87-90. [PMID: 9601603 DOI: 10.1016/s0143-4160(98)90106-3] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The nuclear envelope has a relatively small volume, but is connected up to the vastly larger endoplasmic reticulum. The Ca2+ concentration in the lumen of the interconnected nuclear envelope and endoplasmic reticulum network is in the resting state maintained at a level of more than 100 microM. There are specific Ca2+ release channels present in the inner nuclear membrane that can be activated by inositol trisphosphate or cADP ribose. The system, therefore, allows selective release of Ca2+ into the nucleoplasm which could be important for the control of specific types of gene expression.
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Affiliation(s)
- O H Petersen
- MRC Secretory Control Research Group, Physiological Laboratory, University of Liverpool, UK
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