Platelet sodium hydrogen exchanger activity in normotensives and hypertensives

Increased activity of sodium/hydrogen exchange provides a potentially impor tant mechanism for the development of hypertension. The aims of this study were to compare platelet sodium/hydrogen exchanger activity and renal acid- base excretion in normotensives and hypertensives of Caucasian origin. Plat elet intracellular pH (pH(i)) was measured using the fluorescent dye BCECF to monitor intracellular pH. Sodium/hydrogen exchanger activity was estimat ed from the recovery of pH(i) clamped to 6.25 with nigericin. Normotensives had supine blood pressures of < 140 and < 90 mmHg; those with essential hy pertension had blood pressures > 150/95 mmHg with no known secondary cause. Measurements of platelet pH(i) and sodium/hydrogen exchanger activity were made on 26 normotensives (ten female, sixteen male) and 25 hypertensives ( five female, twenty male). All subjects were on their usual dietary sodium intake. Statistical analysis was by two-way analysis of variance for gender and blood pressure status. Group values are expressed as means +/- SD and a P value of < 0.05 was taken as being statistically significant. There wer e no significant differences in platelet pH(i) between the normotensive (n = 26) and the hypertensive (n = 25) group: pH(i) 7.21 +/- 0.14 and 7.18 +/- 0.16, respectively. The pH(i) recovery after acidification was sodium-depe ndent and inhibited by N-hexamethylene amiloride. Comparison of kinetic con stants showed no significant differences between the normotensive and the h ypertensive groups: values for rate constants and initial velocities were 0 .24 +/- 0.04 s(-1), 0.16 +/- 0.03 dpH(i)/s for the normotensives and 0.25 /- 0.05 s(-1), 0.16 +/- 0.03 dpH(i)/s for the hypertensives, respectively; there were also no significant differences in proton fluxes. The inability to find raised platelet sodium/hydrogen exchanger in the hypertensives cont rasts with previous observations using other methods for the measurement of this exchanger in platelets and this raises important methodological issue s in the assessment of platelet sodium/hydrogen exchanger activity. (C) 199 9 Elsevier Science B.V. All rights reserved.