Pilocarpine and carbachol exhibit markedly different patterns of Ca2+ signaling in rat pancreatic acinar cells.
The effects of the partial muscarinic agonist pilocarpine on physiological responses were investigated in rat pancreatic acinar cells and compared with carbachol, a full muscarinic agonist, together with previous results using JMV-180, a partial agonist of CCK-A receptors. Pilocarpine was found to stimulate amylase release from isolated pancreatic acini in a concentration-dependent manner. At a maximal concentration (10 microM), pilocarpine was only capable of stimulating 63% of the secretion stimulated by a maximal concentration of carbachol. Moreover pilocarpine did not induce a decrease in secretion at supramaximal concentrations as does carbachol. In acini loaded with fura-2, superfusion of pilocarpine resulted exclusively in generation of intracellular Ca2+ concentration ([Ca2+]i) oscillations at all concentrations tested (0.3 microM-1 mM), in marked contrast to high concentrations of full agonists, which result in a biphasic sustained increase in [Ca2+]i. In common with low concentrations of other secretagogues that stimulate [Ca2+]i oscillations, pilocarpine at all concentrations was only able to stimulate a very small increase in phosphoinositide (PI) hydrolysis. In acini previously incubated with [3H]inositol, pilocarpine was shown to stimulate PI hydrolysis 27% above basal, compared with 872% for carbachol. To ascertain if this small degree of PI hydrolysis seen with pilocarpine is responsible for the generation of [Ca2+]i oscillations, an inhibitor of phospholipase C-linked processes, U-73122, which has been shown to inhibit Ca2+ oscillations induced by carbachol and CCK but not JMV-180 was tested. This agent rapidly inhibited pilocarpine-stimulated oscillations, indicating that in contrast to JMV-180, oscillations induced by pilocarpine are the result of PI hydrolysis.
Yule
D I
DI
Department of Physiology, University of Michigan, Ann Arbor 48109-0622.
Essington
T E
TE
Williams
J A
JA
D000681:Amylases / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000502:physiology*; D002217:Carbachol / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005456:Fluorescent Dyes; D016257:Fura-2 / Q000031:analogs & derivatives; D066298:In Vitro Techniques; D007294:Inositol / Q000378:metabolism; D007295:Inositol Phosphates / Q000378:metabolism*; D008297:Male; D010179:Pancreas / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D010716:Phosphatidylinositols / Q000378:metabolism; D010862:Pilocarpine / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects*; D012844:Sincalide / Q000494:pharmacology
D005456:Fluorescent Dyes; D007295:Inositol Phosphates; D010716:Phosphatidylinositols; D010862:Pilocarpine; C049925:fura-2-am; D007294:Inositol; D002217:Carbachol; D000681:Amylases; D012844:Sincalide; D002118:Calcium; D016257:Fura-2