Different patterns of receptor-activated cytoplasmic Ca2+ oscillations in single pancreatic acinar cells: dependence on receptor type, agonist concentration and intracellular Ca2+ buffering.
Agonist-specific cytosolic Ca2+ oscillation patterns can be observed in individual cells and these have been explained by the co-existence of separate oscillatory mechanisms. In pancreatic acinar cells activation of muscarinic receptors typically evokes sinusoidal oscillations whereas stimulation of cholecystokinin (CCK) receptors evokes transient oscillations consisting of Ca2+ waves with long intervals between them. We have monitored changes in the cytosolic Ca2+ concentration ([Ca2+]i) by measuring Ca2(+)-activated Cl- currents in single internally perfused mouse pancreatic acinar cells. With minimal intracellular Ca2+ buffering we found that low concentrations of both ACh (50 nM) and CCK (10 pM) evoked repetitive short-lasting Ca2+ spikes of the same duration and frequency, but the probability of a spike being followed by a longer and larger Ca2+ wave was low for ACh and high for CCK. The probability that the receptor-evoked shortlasting Ca2+ spikes would initiate more substantial Ca2+ waves was dramatically increased by intracellular perfusion with solutions containing high concentrations of the mobile low affinity Ca2+ buffers citrate (10-40 mM) or ATP (10-20 mM). The different Ca2+ oscillation patterns normally induced by ACh and CCK would therefore appear not to be caused by separate mechanisms. We propose that specific receptor-controlled modulation of Ca2+ signal spreading, either by regulation of Ca2+ uptake into organelles and/or cellular Ca2+ extrusion, or by changing the sensitivity of the Ca2(+)-induced Ca2+ release mechanism, can be mimicked experimentally by different degrees of cytosolic Ca2+ buffering and can account for the various cytosolic Ca2+ spike patterns.
Petersen
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MRC Secretory Control Research Group, Physiological Laboratory, University of Liverpool, UK.
Toescu
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Petersen
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D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D002021:Buffers; D002118:Calcium / Q000378:metabolism*; D018118:Chloride Channels; D003593:Cytoplasm / Q000378:metabolism; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D008565:Membrane Proteins / Q000502:physiology*; D051379:Mice; D008954:Models, Biological; D010179:Pancreas / Q000166:cytology / Q000378:metabolism*; D011949:Receptors, Cholecystokinin / Q000187:drug effects / Q000502:physiology*; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000502:physiology*; D012844:Sincalide / Q000494:pharmacology*
D002021:Buffers; D018118:Chloride Channels; D007473:Ion Channels; D008565:Membrane Proteins; D011949:Receptors, Cholecystokinin; D011976:Receptors, Muscarinic; D012844:Sincalide; D000109:Acetylcholine; D002118:Calcium