Digitalis 'receptors' during chronic digoxin treatment.

The effect of digoxin treatment on Mg-dependent [Na+-K+]-ATPase (the receptor for cardiac glycosides) was assessed by comparison of intracellular Na+-K+, 86Rb uptake and number of digoxin binding sites in the erythrocytes of 138 patients on long term digoxin and of 133 control subjects. The parameters were also assessed in thirty-two patients followed longitudinally for 1 y. The results indicate that the cells adapt to chronic exposure to 'therapeutic' dosage of digoxin with an overcompensatory synthesis of new receptors, a possible mechanism through which the normal intraerythrocytic ionic equilibrium is re-established. The process of synthesis of new receptors appears to be completed in erythrocytes in a period of 4 months after the start of digoxin treatment.