The regulation of the Na+ -Ca2+ exchanger of heart sarcolemma.
The Na+/Ca2+-exchange of calf-heart sarcolemma is activated by a treatment with ATP, Mg2+, and Ca2+, and deactivated by a treatment with phosphorylase phosphatase. The effect of the latter can be substituted by a treatment with Mg2+, Ca2+, and calmodulin. The activating treatment does not require added calmodulin, but is inhibited by calmodulin antagonists. Evidently, endogenous calmodulin is required and sufficient. Activation is half-maximal at about 2 microM Ca2+. Added calmodulin, however, decreases the Km (Ca2+) of the activating process to about 0.8 microM. Deactivation is half-maximal, at optimal calmodulin concentrations, at about 1.5 microM Ca2+. Experiments with adenosine 5'-[gamma-thio]triphosphate have shown that the activating treatment is mediated by a kinase and the deactivating treatment by a phosphatase. The concerted operation of the two enzymes is made possible by their different Ca2+ affinity. At saturating Ca2+ concentrations, the level of ATP may also influence the balance of the two enzymes.
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000494:pharmacology; D002417:Cattle; D004789:Enzyme Activation / Q000187:drug effects; D009206:Myocardium / Q000201:enzymology / Q000378:metabolism*; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism; D010766:Phosphorylation; D010770:Phosphotransferases / Q000378:metabolism; D012508:Sarcolemma / Q000201:enzymology / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
D002147:Calmodulin; D012964:Sodium; D010770:Phosphotransferases; D010744:Phosphoric Monoester Hydrolases; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium