Flash photolysis studies of the localization of calcium release sites in rat parotid isolated acinar cells.
1. The temporal relationship between cytosolic free Ca2+ concentration ([Ca2+]i) and activation of membrane current responses in single rat parotid acinar cells has been examined. Activation of muscarinic receptors by carbachol (CCh) at -40 mV (midway between EK and ECl under our experimental conditions) frequently evoked biphasic current responses, application of 2 microM CCh leading to rapid activation of an inward current followed by a slower outward current. 2. Photochemical release of inositol 1,4,5-trisphosphate (InsP3), from 'caged' InsP3, by a brief near-UV flash, evoked similar biphasic current responses at -40 mV. In contrast, elevation of [Ca2+]i by photolysis of the caged calcium compound nitr-5 at -40 mV activated only monophasic current responses. 3. These results can be explained by a model in which the InsP3-sensitive Ca2+ release sites are localized at the luminal pole of the cell, combined with a relative preponderance of Ca(2+)-activated Cl- channels at that pole, and a relative preponderance of Ca(2+)-activated K+ channels at the basal end.
Hassoni
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Department of Pharmacology, School of Pharmacy, London, UK.
Gray
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PT
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism; D018721:Muscarinic Agonists / Q000494:pharmacology; D010306:Parotid Gland / Q000166:cytology / Q000378:metabolism* / Q000528:radiation effects; D018408:Patch-Clamp Techniques; D010782:Photolysis; D051381:Rats; D011976:Receptors, Muscarinic / Q000187:drug effects; D014466:Ultraviolet Rays
D002614:Chelating Agents; D007473:Ion Channels; D018721:Muscarinic Agonists; D011976:Receptors, Muscarinic; C052455:nitr 5; D004533:Egtazic Acid; D015544:Inositol 1,4,5-Trisphosphate; D002217:Carbachol; D002118:Calcium