Inhibition of red cell Na+,K+-ATPase in digitalized patients

Erythrocyte 3H-ouabain binding and digitalis treatment in ethanol addicted patients

The binding of 3H-ouabain to human erythrocytes was analyzed in a population of hospitalized male ethanol addicted patients under long term digitalis treatment. In the non-alcoholic patient group the long term digitalis treatment induced an increase in Bmax and Kd values; such modification was not observed in the alcoholic patients. Chronic alcohol intake itself induced an increase in 3H-ouabain kinetic parameters. These observations confirm that ouabain binding to human erythrocytes is subject to pharmacological and toxicological regulation and that adaptive changes in peripheral tissues can be useful in predicting possible parallel modifications in other less accessible tissues.

Erythrocyte Na+, K+-ATPase and serum digoxin concentrations

Digoxin therapy has been made more rational by the measurement of serum digoxin concentrations. However, difficulties remain because of the overlap between "therapeutic" and "toxic" serum concentrations and the lack of an obvious therapeutic endpoint in many patients. An assay which measures the degree of interaction between digoxin and its putative receptor, the membrane Na+, K+-ATPase, might be capable of resolving some of these difficulties. Therefore, as a first approach in this direction we evaluated the relationship between serum digoxin concentration and the degree of inhibition of RBC ghost Na+, K+-ATPase activity in patients receiving digoxin therapy. Utilizing an improved micro-assay technique, Na+, K+-ATPase activity was determined in aliquots of RBC ghosts before and after removal of bound digoxin. In 27 patients a significant relationship was present between serum digoxin concentration and the degree of RBC ghost Na+, K+-ATPase inhibition. However, at any serum digoxin concentration, there was a variation in the magnitude of enzyme inhibition from patient to patient. This study confirms the feasibility of determining the degree of in vivo RBC Na+, K+-ATPase inhibition in man and demonstrates, for the first time, a highly significant but somewhat variable relationship between serum digoxin concentrations and the magnitude of RBC digoxin receptor inactivation. This quantitative, functional, individualized assay of digoxin effects may prove to be of clinical value in the future.

The role of active sodium and potassium transport in hyponatremic states in infancy and childhood

Erythrocytes from 14 infants and children with serum sodium concentrations of 125 mmol/l or less were analyzed for total and Na+, K+-ATPase, sodium and potassium content and ATP concentrations to evaluate the role of active Na+-K+ transport in hyponatremia. In six out of nine patients, with a duration of hyponatremia of more than 48 hours low Na+, K+-ATPase activities and high erythrocyte sodium concentrations and Na+-K+ ratios were found indicating that a decreased Na+, K+-ATPase activity leading to an increased intracellular accumulation of sodium ions may have reduced the extracellular sodium concentration. Three subjects with large sodium losses had high Na+, K+-ATPase activities and normal erythrocyte sodium concentrations. In five cases of hyponatremia with a duration of less than 24 hours the variables indicating active Na+-K+ transport were normal. The therapeutic implications with sodium substitution and the use of drugs affecting active Na+-K+ transport are discussed.

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.