Two components of hormone-evoked calcium release from intracellular stores of pancreatic acinar cells.
Dispersed pancreatic acini loaded with Fura 2 were used to study the effect of hormonal stimulation on [Ca2+]i (free cytosolic Ca2+ concentration). Stimulation of acini with cholecystokinin octapeptide or carbachol resulted in two components of increase in [Ca2+]i. The maximal increase in [Ca2+]i and the time to maximum for both components was dependent on hormone concentration. The first component reached a maximum after 2-10 s of stimulation, whereas the second component required 30-60 s of stimulation for maximal effect. Both components of the [Ca2+]i increase can be observed in the presence or absence of Ca2+ in the incubation medium. The two components of Ca2+ release from intracellular stores showed similar dependency on agonist concentration. Termination of cell stimulation with specific antagonist revealed two, kinetically separated, rates of decrease in [Ca2+]i. The initial decrease in [Ca2+]i, was completed within 2.5-7 s, whereas the secondary decrease in [Ca2+]i, back to resting values, required approx. 40 s. The magnitude of the antagonist-induced initial (rapid) and secondary (slow) decrease in [Ca2+]i was dependent on the duration of cell stimulation. Hence it appears that stimulation of pancreatic acinar cells with Ca2+-mobilizing hormones results in two, kinetically separated, components of Ca2+ release from intracellular stores.
Muallem
S
S
Laboratory of Membrane Biology, Cedars-Sinai Medical Center, Los Angeles, CA 90048.
Pandol
S J
SJ
Beeker
T G
TG
D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology*; D066298:In Vitro Techniques; D007424:Intracellular Fluid / Q000187:drug effects / Q000378:metabolism; D007700:Kinetics; D010179:Pancreas / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D012844:Sincalide / Q000494:pharmacology*; D013268:Stimulation, Chemical
D001285:Atropine; D002217:Carbachol; D012844:Sincalide; D002118:Calcium