[Influence of beta 1-methyl-digoxin to red cell electrolyte contents in healthy normals (author's transl)]

Influence of digitalis and diuretics on ouabain binding sites on human erythrocytes

It has been reported that during chronic treatment with digitalis, the number of digitalis binding sites is increased in human erythrocytes [22]. From this finding a tachyphylaxis for cardiac glycosides has been postulated. We reinvestigated this problem in several groups of patients. The number of 3H-ouabain binding sites per erythrocyte in control persons (group I) was 214 +/- 60, n = 43 (means +/- SD). The dissociation constant (KD) was 1.8 +/- 0.5 nM. Thirteen patients (group II) taking cardiac glycosides only, for at least 6 months, had 281 +/- 99 (p less than 0.05) ouabain binding sites per single red cell, KD = 1.8 +/- 0.7 nM. Group III (34 patients) took digitalis for more than 6 months and diuretics for at least 3 months (352 +/- 126 (p less than 0.001), KD = 1.6 +/- 0.6). Twenty-three of these (group IV) were taking a combination with "K+-saving" diuretics (336 +/- 194 (p less than 0.01), KD = 1.6 +/- 0.5) and (group V, 11 patients) a combination with "K+-losing" diuretics (462 +/- 133 (p less than 0.001), KD = 1.4 +/- 0.4). Nine patients (group VI) had a chronic hypokalemia, mainly due to taking furosemide (437 +/- 98 (p less than 0.001), KD = 1.5 +/- 0.4). Four control persons took 50 mg hydrochlorothiazide daily for more than 4 months without measurable K+-losses and without changes in ouabain binding sites. It is concluded from these findings that diuretic treatment with chronic hypokalemia in addition to digitalis is accompanied by a significant increase in ouabain binding sites in human red cells.(ABSTRACT TRUNCATED AT 250 WORDS)

[The problem of the cellular receptor for cardiac glycosides (author's transl)]

This review concerns the Na+, K+ -ATPase as well as the Na+, K+ -pump in the intact membrane and the highly specific inhibition of this transport system by cardiac glycosides. The interaction between glycoside and enzyme and the regulation of the kinetics of glycoside binding by ATP, K+, Na+, Mg2+ and Ca2+ are described. Emphasis is placed on the significance of the Na+, K+ -pump as the pharmacological receptor for cardiac glycosides. The problem encountered and progress made in attempting to correlate the inotropic action of cardiac glycosides with the binding of these drugs to the heart muscle and with the inhibition of the Na+, K+ -pump are reported. Recent results concerning increases of the intracellular Na+ concentration which are obtained by a partial inhibition of the Na+, K+ -pump and which are followed by an elevation of the intracellular Ca2+ -activity are reviewed. The discovery of a digitalis-like endogenous activity corresponds to the high specificity of the receptor for cardiac glycosides.

The erythrocyte sodium and potassium in patients treated with digoxin

1 Four healthy persons and ten patients with heart failure were studied for 5 to 20 days after they started taking digoxin. The sodium content of their erythrocytes increased and there was an equimolar decrease in potassium content. 2 The increase in erythrocyte sodium for a given increase in plasma digoxin during this acute digitalization was less on average and varied more in the patients than in the healthy persons, that is the patients' erythrocytes were less responsive to digoxin. 3 The average erythrocyte sodium was greater in 183 patients who had been taking digoxin for at least 2 months than in 100 healthy persons not taking digoxin but there was no significant correlation between the plasma digoxin concentrations and erythrocyte sodium concentration in the patients. Indeed, there was no apparent change in the erythrocyte sodium in many of the patients taking digoxin. 4 If the erythrocyte sodium concentration is a reliable guide to the tissue effects of digoxin then the results suggest that there is a wide variation in the response to digoxin between patients both during acute digitalization and during chronic treatment with digoxin.

High erythrocyte membrane (Na+ + K+)-ATPase in kwashiorkor, in vivo reversal by diuretic

Specific activity (mumol Pi released/h/mg membrane protein) of ouabain-sensitive (Na+ + K+)-ATPase has been shown to be higher in erythrocytes from children suffering from kwashiorkor, compared to that in normal children. Twenty four hours after treatment of these children with a diuretic, there was reduction in their body weights due to loss of oedema fluid. Ouabain sensitive (Na+ + K+)-ATPase of the erythrocyte membrane was inhibited by about 40% and this was associated with gain of 1.8 mequivalents Na+ per litre of erythrocytes. The results suggest that high ouabain-sensitive (Na+ + K+)-ATPase could be one of the mechanisms operative in erythrocytes to prevent accumulation of Na+ in kwashiorkor.