Platelet Na+-H+ exchanger activity in normotensive and hypertensive subjects: 
effect of enalapril therapy upon antiport activity

Rosskopf, Dieter; Siffert, Gerlinde; Osswald, Ursula; Witte, Klaus; Düsing, Rainer; Akkerman, Jan Willem; Siffert, Winfried

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Platelet Na⁺-H⁺ exchanger activity in normotensive and hypertensive subjects: effect of enalapril therapy upon antiport activity

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Rosskopf, Dieter
Department of Physiology, Max Planck Institute of Biophysics, Max Planck Society;

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Siffert, Gerlinde
Department of Physiology, Max Planck Institute of Biophysics, Max Planck Society;

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Siffert, Winfried
Department of Physiology, Max Planck Institute of Biophysics, Max Planck Society;

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Citation

Rosskopf, D., Siffert, G., Osswald, U., Witte, K., Düsing, R., Akkerman, J. W., et al. (1992). Platelet Na⁺-H⁺ exchanger activity in normotensive and hypertensive subjects: effect of enalapril therapy upon antiport activity. Journal of Hypertension, 10(8), 839-847.

Cite as: https://hdl.handle.net/21.11116/0000-000A-8381-F

Abstract

Objective: Primary hypertension has been reported to be associated with an enhancement of Na⁺-H⁺ exchange. However, details of the kinetic properties of the Na⁺-H⁺ exchanger in hypertensives and its dependence upon age and gender in normotensives are unknown.

Participants: We determined the activity of the platelet Na⁺-H⁺ exchanger in 20 normotensives and 26 untreated primary hypertensives.

Interventions: In eight hypertensive individuals antihypertensive treatment was interrupted for 1 week. Treatment for 6 weeks with a daily single dose of 10 mg enalapril decreased mean arterial pressure to 105.7 ± 11.6 mmHg.

Methods: Platelets were loaded with the intracellular pH (pH_i) indicator 2'-7'-bis-carboxyethyl-5(6)-carboxyfluorescein (BCECF) and acidified by propionic acid. Initial velocities of pH recovery were determined and used for calculation of maximum velocity (V_max), baseline pH_i and the pH_i value for half maximal activation (pH0.5) of the Na⁺-H⁺ exchanger in each individual.

Results: In normotensives, V_max averaged 0.05 ± 0.01 dpH_i/min independently of age, gender and actual diastolic blood pressure. In hypertensives, two different subgroups were defined bearing either low or high Na⁺-H⁺ exchange activity. Values of pH_iexchange activity. Values of pH and pH0.5 were identical in all subgroups irrespective of V_max. The twofold enhancement of Na⁺-H⁺ exchange in the second group was preserved in thrombin-stimulated platelets. V_max values remained unaffected by enalapril treatment.

Conclusions: Enhanced Na⁺-H⁺ exchange activity in hypertensives is primarily characterized by an increase in V_max. This enhancement is refractory to antihypertensive treatment and therefore appears to be a relatively fixed parameter.