SODIUM-DEPENDENT CARDIAC GLYCOSIDE BINDING - EXPERIMENTAL-EVIDENCE AND HYPOTHESIS

The influence of increasing Na+ concentrations on the binding of digitoxin, digoxin and ouabain was examined in a Na+‐K+‐ATPase preparation of guinea‐pig hearts Two distinct processes seem to be involved in this interaction: one binding process was activated at low Na+ concentrations. The maximum binding capacities were different and the K0.5 values were nearly identical for the cardiac glycosides studied. In contrast, the second binding process was activated at appreciably higher Na+ concentrations, the maximum binding capacities were almost identical and the K0.5 values were different for the cardiac glycosides studied. On the basis of these results attempts are made to explain the well known differences in the myocardial accumulation of cardiac glycosides. 1978 British Pharmacological Society