Heterogeneity of ouabain specific binding sites and (Na+ + K+)-ATPase inhibition in microsomes from rat heart.
Cardiac glycoside binding to microsomes prepared from rat heart ventricles and enriched in (Na+ + K+)-ATPase was measured by a rapid filtration technique. The relation between ouabain binding to microsomes and (Na+ + K+)-ATPase activity has also been examined. Data were statistically analysed by means of two different non linear regression methods. The experimental results were fitted the most closely by a model describing that ouabain specific binding occurred at two classes of independent sites. High affinity sites were characterized by a dissociation constant of 0.21 +/- 0.01 microM and a low capacity (9.4 +/- 1.4 pmoles/enzymatic unit). Low affinity sites were characterized by a dissociation constant equal to 13 +/- 3 microM and a capacity equal to 87 +/- 15 pmoles/enzymatic unit. Similar results were obtained with the more lipophilic glycoside digoxin. It was also observed that dihydroouabain, a ouabain derivative with a saturated lactone ring, competes with 3H-ouabain for the binding to the two classes of sites. Binding to these two classes of sites appeared to be associated with a corresponding inhibition of (Na+ + K+)-ATPase activity.
D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D004077:Digoxin / Q000378:metabolism; D005260:Female; D005374:Filtration; D008861:Microsomes / Q000201:enzymology; D008954:Models, Biological; D009206:Myocardium / Q000201:enzymology*; D010042:Ouabain / Q000031:analogs & derivatives / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors*
C000977:dihydroouabain; D010042:Ouabain; D004077:Digoxin; D000254:Sodium-Potassium-Exchanging ATPase