title: Effects of calcium on the heterogeneity of the Na+, K+-ATPase forms in rat heart.
abstract: The sensitivity of the Na+, K+-ATPase to ouabain has been studied in sarcolemma vesicles isolated from normal rat heart. Two enzyme forms exhibiting high and low sensitivities to ouabain have been observed in Ca2+-free perfused heart. The half-maximal inhibitory effects occurred with 1-2 X 10(-8) M ouabain. The high sensitivity form undetectable in hearts maintained at a physiological Ca2+ level might represent altered low affinity sites or latent enzyme forms unmasked by low calcium concentrations. The heterogeneity of the Na+, K+-ATPase forms was found to be also modulated by the K+/ouabain antagonism, addition of K+ accentuating the heterogeneity. These in vitro results associated with in vivo experiments on isolated rat heart working under isovolumic conditions suggested that lowering Ca2+ has qualitative and quantitative effects. Low Ca2+ concentrations increased the sensitivities to ouabain and the amplitudes of both the enzyme inhibition and the positive inotropic effects.
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism; D009206:Myocardium / Q000201:enzymology*; D010042:Ouabain / Q000494:pharmacology*; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011955:Receptors, Drug / Q000187:drug effects*; D012508:Sarcolemma / Q000201:enzymology; D000254:Sodium-Potassium-Exchanging ATPase / Q000032:analysis* / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D007527:Isoenzymes; D011955:Receptors, Drug; C028996:cardiac glycoside receptors; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium; D002118:Calcium