Changes in cardiac glycoside receptor sites, 86rubidium uptake and intracellular sodium concentrations in the erythrocytes of patients receiving digoxin during the early phases of treatment of cardiac failure in regular rhythm and of atrial fibrillation.

1 Measurements of the binding of 12-alpha-[3H]-digoxin to the membranes of intact erythrocytes, erythrocytic 86rubidium uptake and intraerythrocytic sodium concentrations have been made in the red cells of patients receiving digoxin in the short-term for atrial fibrillation or cardiac failure in regular rhythm. 2 During the first few days of treatment [3H]-digoxin binding and 86rubidium uptake fall and intraerythrocytic sodium concentrations rise. 3 Subsequently parallel fluctuations occur in [3H]-digoxin binding and 86rubidium uptake but not in intraerythrocytic sodium concentrations and the significance of the fluctuations is discussed. 4 The values of all three measurements correlate significantly with the response of the heart in sinus rhythm as measured by QS2I. 5 Plasma digoxin concentrations do not correlate with QS2I.