Carbachol partially inhibits the plasma-membrane Ca2+-pump in microsomes from pig stomach smooth muscle.
A plasmalemmal enriched membrane fraction, prepared from pig stomach smooth-muscle, contains a calmodulin-stimulated (Ca2+ + Mg2+)-ATPase and presents an ATP-dependent 45Ca-uptake. If these smooth-muscle strips are preincubated with 10(-3) M-carbachol, this Ca2+ + Mg2+)-ATPase and the 45Ca-uptake are reduced by 21.4% and 13.5%, respectively, as compared to controls. This inhibitory effect of carbachol can be completely blocked by atropine. Carbachol does neither affect the passive permeability of the microsomes to 45Ca, nor the passive 45Ca-binding to the vesicles. Neither does it exert an effect on the proportion of closed inside-out plasma-membrane vesicles. Likewise, preincubation of rat myometrium with 90 nM-oxytocin induces a 20.4% inhibition of the ATP-dependent 45Ca-uptake, without having an effect on the passive 45Ca-binding, the permeability to 45Ca or the sideness of the vesicles. From these results, it is concluded that some agonists as carbachol and oxytocin induce a decrease in the activity of the plasmalemmal Ca2+-pump.
D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000037:antagonists & inhibitors*; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors*; D002147:Calmodulin / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology*; D002462:Cell Membrane / Q000378:metabolism; D008861:Microsomes / Q000187:drug effects / Q000378:metabolism*; D009130:Muscle, Smooth / Q000378:metabolism*; D011706:Pyloric Antrum / Q000378:metabolism; D013552:Swine
D002147:Calmodulin; D002217:Carbachol; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D002118:Calcium