The characteristics of the binding of 12‐alpha‐[3H]‐digoxin to the membranes of intact human erythrocytes: relevance to digoxin therapy.

Abstract

1 The characteristics of the binding of 12‐alpha‐[3H]‐digoxin to the membranes of intact human erythrocytes are described. 2 Only one class of binding site can be demonstrated. Binding is time‐ and temperature‐ dependent, saturable and slowly reversible; it is inhibited by other cardiac glycosides and by potassium. 3 Pre‐incubation with unlabelled digoxin reduces the subsequent binding of 12‐alpha‐[3H]‐digoxin in stoichiometric fashion. 4 The possible application of the measurement of the binding of 12‐alpha‐[3H]‐digoxin to the study of biochemical pharmacological events occurring during digoxin therapy is discussed.

The characteristics of [3H]‐ouabain binding to human lymphocytes.

“…In uptake and release studies ( Figure 5 and Figure 6), the use of rather high radioligand concentrations ensured a true equilibrium to be accomplished within about 2 h. The mean dissociation constant (k_L/k+1) calculated from these experiments was 0.512 x 10-8 M, which is only slightly less the value derived from Scatchard analysis. (Erdmann et al, 1975;Ford et al, 1979;Kaji et al, 1981). Since the cell surface of the erythrocyte is only slightly less that of the lymphocyte, the latter has clearly a much higher receptor density.…”

“…Most studies on pump function have used erythrocytic Na+/K+ ATRase preparations (Erdmann et al, 1975;Ford et al, 1979;Gardner & Conlon, 1972;Gardner etal., 1973;Kaji etal., 1981). However, this highly specialized cell may be less relevant to study, since it possesses comparatively few pump sites (300/ cell) (Erdmann et al, 1975) and is devoid of a DNAnucleus, which prohibits synthesis of pumps de novo.…”

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.

“…Furthermore we have measured patients' intraerythrocytic cation concentrations and the capacity of their erythrocyte membranes to bind 12-a-[3HJ-digoxin in vitro during the early stages of digoxin therapy. The characteristics of this binding in normal subjects have already been described (Ford, Aronson, Grahame-Smith & Rose, 1979).…”

The acute changes seen in cardiac glycoside receptor sites, 86rubidium uptake and intracellular sodium concentrations in the erythrocytes of patients during the early phases of digoxin therapy are not found during chronic therapy: pharmacological and therapeutic implications for chronic digoxin therapy.

“…The observation that cardiac glycosides inhibit sodium and potassium transport in erythrocytes (Schatzmann, 1953) and the supposition that this inhibition is due to inhibition of Na+, K+-ATPase activity consequent upon binding of glycoside to the enzyme have formed the basis of our approach. In vitro incubation of human erythrocytes with varying concentrations of cardiac glycosides results in the following concentration-related phenomena: (a) inhibition of the subsequent capacity of the membranes of intact cells to bind [3H]-digoxin in vitro (Ford, Aronson, Grahame-Smith & Rose, 1979a); (b) inhibition of in vitro 86rubidium transport into the cells ; (c) increases in intracellular sodium concentrations (unpublished observations).…”