Further investigation of platelet cytosolic alkalinization in essential hypertension.

OBJECTIVE: To verify that platelet cytosolic pH is altered in essential hypertension and to investigate the mechanisms involved. METHODS: Cytosolic pH was determined in unstimulated platelets by the fluorescent indicator 2,7-bis-carboxyethyl-5(6)-carboxyfluorescein (BCECF). Membrane microviscosity was evaluated by the fluorescence anisotropies of diphenylhexatriene (DPH) and its cationic derivative trimethylamino-diphenylhexatriene (TMA-DPH). RESULTS: The cytosolic alkalinization previously observed in platelets from untreated hypertensive patients was confirmed. The buffering capacity appeared unaltered and the cytosolic pH was not modified by 50 mumol/l N-5-ethylisopropylamiloride, a specific inhibitor of the Na(+)-H+ exchange. Exposure to external Na(+)-free media produced an intracellular acidification that was similar in hypertensive and normotensive donors and maintained the cytosolic pH difference between the two groups. In the two blood pressure groups platelet cytosolic pH varied inversely with the steady-state anisotropy of TMA-DPH but not with that of DPH. Experimentally induced acidification of the cytosol by Na+ removal with or without nigericin treatment was accompanied by rises in TMA-DPH anisotropy. CONCLUSIONS: This study of platelet intracellular pH in essential hypertension confirms cytosolic alkalinization and demonstrates its association with changes in the dynamic properties of the platelet plasma membrane.