title: Thapsigargin defines the roles of cellular calcium in secretagogue-stimulated enzyme secretion from pancreatic acini.
abstract: In the present study we used thapsigargin (TG), an inhibitor of microsomal calcium ATPase, to evaluate the roles of free cytoplasmic calcium and intracellular stored calcium in secretagogue-stimulated enzyme secretion from rat pancreatic acini. Using microspectrofluorimetry of fura-2-loaded pancreatic acini, we found that TG caused a sustained increase in free cytoplasmic calcium by mobilizing calcium from inositol 1,4,5-trisphosphate-sensitive intracellular stores and by increasing influx of extracellular calcium. TG also caused a small increase in basal amylase secretion, inhibited the stimulation of amylase secretion caused by secretagogues that increase inositol 1,4,5-trisphosphate, and potentiated the stimulation of amylase secretion caused by 12-O-tetradecanoylphorbol-13-acetate or secretagogues that increase cyclic adenosine 3',5'-monophosphate. Bombesin, which like TG increased free cytoplasmic calcium, also potentiated the stimulation of amylase secretion caused by secretagogues that increase cyclic adenosine 3',5'-monophosphate, but did not inhibit the stimulation of amylase secretion caused by secretagogues that increase inositol 1,4,5-trisphosphate. Finally, TG inhibited the sustained phase of cholecystokinin-stimulated amylase secretion and potentiated the time course of vasoactive intestinal peptide-stimulated amylase secretion. The present findings indicate that stimulation of amylase secretion by secretagogues that increase inositol 1,4,5-trisphosphate does not depend on increased free cytoplasmic calcium per se. In contrast, TG-induced potentiation of the stimulation of secretagogues that increase cellular cyclic adenosine 3',5'-monophosphate appears to result from increased free cytoplasmic calcium per se.
authors.affiliation: Digestive Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: D C
authors.initials: DC
authors.lastname: Metz
authors.forename: R J
authors.initials: RJ
authors.lastname: Patto
authors.forename: J E
authors.initials: JE
authors.lastname: Mrozinski
authors.forename: R T
authors.initials: RT
authors.lastname: Jensen
authors.forename: R J
authors.initials: RJ
authors.lastname: Turner
authors.forename: J D
authors.initials: JD
authors.lastname: Gardner
mesh_terms: D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000681:Amylases / Q000378:metabolism*; D000818:Animals; D001839:Bombesin / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors*; D002217:Carbachol / Q000494:pharmacology; D003593:Cytoplasm / Q000378:metabolism; D016257:Fura-2; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D010179:Pancreas / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012633:Secretin / Q000494:pharmacology; D012844:Sincalide / Q000494:pharmacology; D013050:Spectrometry, Fluorescence; D013729:Terpenes / Q000494:pharmacology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D019284:Thapsigargin; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology
chemical_list: D013729:Terpenes; D012633:Secretin; D015124:8-Bromo Cyclic Adenosine Monophosphate; D014660:Vasoactive Intestinal Peptide; D000001:Calcimycin; D019284:Thapsigargin; D002217:Carbachol; D000681:Amylases; D000252:Calcium-Transporting ATPases; D012844:Sincalide; D013755:Tetradecanoylphorbol Acetate; D001839:Bombesin; D002118:Calcium; D016257:Fura-2