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
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