Erythrocyte Na⁺,K⁺ and Ca²⁺, Mg²⁺-ATPase activities in hypertensives on angiotensin-converting enzyme inhibitors

Objective: To investigate erythrocyte membrane Na⁺,K⁺- and Ca²⁺,Mg²⁺-ATPaSe activities in newly diagnosed hypertensive patients before and after 2, 4, and 6 months of treatment with enalapril or captopril as monotherapy. Methods and Results: Na⁺,K⁺-ATPaSe activity (nmol ATP hydrolysed/min per mg protein) rose by 6 months of treatment in both groups when values were compared in each treated group over time (4.5 ± 0.8 to 9.9 ± 1.2; 4.9 ± 0.8 to 10.5 ± 1.7, respectively, p < 0.001 for both). When the treated groups were compared with controls at each period of time, Na⁺,K⁺-ATPaSe activity was higher at months 4 and 6 (p < 0.001) for both groups, respectively). Ca²⁺,Mg²⁺-ATPaSe activity (nmol ATP hydrolyzed/min per milligram protein) in the absence and in the presence of calmodulin increased in the enalapril (6.4 ± 0.7 to 8.9 ± 0.95, p < 0.05; 13.4 ± 1.2 to 17.2 ± 1.2, p < 0.05, respectively) and captopril (7.0 ± 0.6 to 8.5 ± 0.7; 14.4 ± 1.1 to 16.0 ± 1.0, p < 0.05, respectively) groups after 6 months of treatment compared within each treated group over time. When patient groups were compared with controls at time 0, 2, 4, and 6 months, the pump activity was higher in the treated groups at 6 months. Conclusion: The long-term enhancement of cell membrane Na⁺,K⁺- and Ca²⁺, Mg²⁺-ATPaSe activity associated with enalapril and captopril therapy may represent a specific effect of these agents or alternatively, a nonspecific outcome of blood pressure reduction.