Regulation of calcium transport in pancreatic acinar plasma membranes from guinea pig.
The regulation of the guinea-pig pancreatic acinar plasma membrane Ca2+ pump by protein kinase A, protein kinase C and calmodulin was investigated. The results were compared with the effects of these regulators on the high affinity Ca(2+)-ATPase found in this membrane preparation. The catalytic subunit of cyclic AMP-dependent protein kinase stimulated Ca2+ transport 2-fold, but had no effect on Ca(2+)-dependent ATPase activity. Purified protein kinase C, the phorbol ester 12-O-tetradecanoyl phorbol-13-acetate and diacylglycerol derivative, 1-stearoyl-2-arachidonoyl-sn-glycerol, failed to stimulate the Ca(2+)-uptake but augmented the Ca(2+)-dependent ATPase activity. Exogenously added calmodulin failed to stimulate either activity. In addition, two antagonists of calmodulin activity, trifluoperazine and compound 48/80 produced a concentration-dependent inhibition of Ca(2+)-transport. These data suggest the presence of endogenous calmodulin within guinea-pig pancreatic acinar plasma membranes. Both calmodulin antagonists failed to influence the Ca(2+)-dependent ATPase activity. The ability of boiled extracts from guinea-pig pancreatic acinar plasma membranes to stimulate the Ca(2+)-ATPase activity in calmodulin-depleted erythrocyte plasma membranes confirmed the presence of endogenous calmodulin. Our results imply a role for calmodulin and cAMP-dependent protein kinase, but not protein kinase C, in the regulation of Ca2+ efflux from pancreatic acinar cells. These results also provide further evidence suggesting that the high affinity Ca(2+)-ATPase does not catalyze the plasma membrane Ca(2+)-transport activity observed in pancreatic acini.
Mahey
R
R
Division of Pharmacology and Toxicology, Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, Canada.
Allen
B G
BG
Bridges
M A
MA
Katz
S
S
D000818:Animals; D002118:Calcium / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000378:metabolism* / Q000502:physiology*; D002147:Calmodulin / Q000378:metabolism*; D002462:Cell Membrane / Q000201:enzymology / Q000378:metabolism; D006168:Guinea Pigs; D010179:Pancreas / Q000201:enzymology / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism*
D002147:Calmodulin; D011494:Protein Kinases; D011493:Protein Kinase C; D000252:Calcium-Transporting ATPases; D002118:Calcium