The role of a (Ca2+ + Mg2+)-ATPase of the rough endoplasmic reticulum in regulating intracellular Ca2+ during cholinergic stimulation of rat pancreatic acini.
Rough endoplasmic reticulum membranes, purified from isolated rat pancreatic acini stimulated by carbachol, had a decreased Ca2+ content and increased (Ca2+ + Mg2+)-ATPase activity. Ca2+ was regained and ATPase activity reduced to control levels only after blockade by atropine. The (Ca2+ + Mg2+)-ATPase was activated by free Ca2+ (half-maximal at 0.17 microM; maximal at 0.7 microM) over the concentration range which occurs in the cell cytoplasm. Pretreatment with EGTA, at a high concentration (5 mM), inhibited ATPase activity which, our results suggest, was due to removal of a bound activator such as calmodulin. The rate of (Ca2+ + Mg2+)-ATPase actively declined during the 10-min period over which maximal active accumulation of Ca2+ by membrane vesicles occurs. In the presence of ionophore A23187, which released actively accumulated Ca2+ and stimulated the (Ca2+ + Mg2+)-ATPase, this time-dependent decline in activity was not observed. Our data provide evidence that the activity of the Ca2+-transporting ATPase of the rough endoplasmic reticulum is regulated by both extra and intravesicular Ca2+ and is consistent with a direct role of this enzyme in the release and uptake of Ca2+ during cholinergic stimulation of pancreatic acinar cells.
D000818:Animals; D001285:Atropine / Q000494:pharmacology; D017301:Ca(2+) Mg(2+)-ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology*; D004533:Egtazic Acid / Q000494:pharmacology; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000201:enzymology*; D010179:Pancreas / Q000201:enzymology*; D051381:Rats; D011919:Rats, Inbred Strains; D011950:Receptors, Cholinergic / Q000502:physiology
D011950:Receptors, Cholinergic; D000001:Calcimycin; D004533:Egtazic Acid; D001285:Atropine; D002217:Carbachol; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D002118:Calcium