Calcium mobilizing hormones activate the plasma membrane Ca2+ pump of pancreatic acinar cells.
45Ca fluxes and free-cytosolic Ca2+([Ca2+]i) measurements were used to study the effect of Ca2+-mobilizing hormones on plasma membrane Ca2+ permeability and the plasma membrane Ca2+ pump of pancreatic acinar cells. We showed before (Pandol, S.J., et al., 1987. J. Biol. Chem. 262:16963-16968) that hormone stimulation of pancreatic acinar cells activated a plasma membrane Ca2+ entry pathway, which remains activated for as long as the intracellular stores are not loaded with Ca2+. In the present study, we show that activation of this pathway increases the plasma membrane Ca2+ permeability by approximately sevenfold. Despite that, the cells reduce [Ca2+]i back to near resting levels. To compensate for the increased plasma membrane Ca2+ permeability, a plasma membrane Ca2+ efflux mechanism is also activated by the hormones. This mechanism is likely to be the plasma membrane Ca2+ pump. Activation of the plasma membrane Ca2+ pump by the hormones is time dependent and 1.5-2 min of cell stimulation are required for maximal Ca2+ pump activation. From the effect of protein kinase inhibitors on hormone-mediated activation of the pump and the effect of the phorbol ester 12-0-tetradecanoyl phorbol, 13-acetate (TPA) on plasma membrane Ca2+ efflux, it is suggested that stimulation of protein kinase C is required for the hormone-dependent activation of the plasma membrane Ca2+ pump.
Muallem
S
S
Laboratory of Membrane Biology, Cedars-Sinai Medical Center, Los Angeles, California 90048.
Pandol
S J
SJ
Beeker
T G
TG
D000818:Animals; D001285:Atropine / Q000494:pharmacology; D001693:Biological Transport, Active; D002118:Calcium / Q000493:pharmacokinetics*; D002217:Carbachol / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism*; D002463:Cell Membrane Permeability; D004987:Ethers / Q000494:pharmacology; D006728:Hormones / Q000502:physiology*; D015759:Ionomycin; D007515:Islets of Langerhans / Q000166:cytology / Q000378:metabolism*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D051381:Rats; D012844:Sincalide / Q000502:physiology
D004987:Ethers; D006728:Hormones; D015759:Ionomycin; D001285:Atropine; D002217:Carbachol; D011493:Protein Kinase C; D012844:Sincalide; D002118:Calcium