Abstract
Cardiac glycoside binding to rat heart membrane preparations was measured by rapid filtration technique. The binding data were analyzed using quantitative computer analysis. The experimental results using [3H]-ouabain as the labeled ligand were consistent with a model in which cardiac glycoside specific binding occurs at two independent classes of sites. The high affinity sites were characterized by a dissociation constants of 40 nM, 50 nM, and 61 nM for ouabain, digoxin and digitoxin, respectively, with a binding capacity of 1.3 pmoles/mg protein. The lower affinity sites for ouabain were characterized by dissociation constants of 2.3 µM, 67 nM and 71 nM for ouabain, digoxin and digitoxin, respectively, with a binding capacity of 3 pmoles/mg protein. Potassium ions inhibit [3H]-ouabain binding in a dose dependent manner with an IC50 of 500 µM. Quantitative computer modelling indicated that potassium inhibits ouabain binding at both binding sites.