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Objective: To study the relationship between high blood pressure and hyperlipidaemia and the cytosolic calcium concentration in unstimulated platelets, focusing on the effects of an alteration in membrane dynamics., Materials and Methods: Basal cytosolic calcium concentrations were determined in the presence and the absence of a significant calcium influx in platelets of 47 untreated hypertensive patients and 26 normotensive subjects. Membrane microviscosity was investigated by fluorescence depolarization of diphenylhexatriene and trimethylaminodiphenylhexatriene. To study the influence of plasma factors, unstimulated platelets were loaded in the presence of plasma with Quin-2, which forms a relatively strong intracellular calcium buffer. The cytosolic calcium concentration was then determined at two extracellular calcium concentrations (1 mmol/l and in the absence of a Ca2+ influx)., Results: Irrespective of the external calcium concentration, the cytosolic calcium concentration increased significantly with diastolic blood pressure (P = 0.026 in the presence and P = 0.003 in the absence of Ca2+ influx) and with plasma triacylglycerols (P = 0.03 and 0.001, respectively). Multiple regression analysis indicated that the cytosolic Ca+ concentration was independently related to these two factors [Ca2+ = 35 + (18.6 +/- 4.6). In triacylglycerols (mmol/l) + (0.45 +/- 0.15) mmHg diastolic blood pressure; P < 0.001]. The relationship between the cytosolic calcium concentration and diphenylhexatriene or trimethylaminodiphenylhexatriene anisotropies was not independent of blood pressure and plasma triacylglycerol levels., Conclusions: The present results confirm the link between blood pressure and the platelet cytosolic calcium concentration and indicate that plasma triacylglycerols directly or indirectly modulate the ex vivo efficacy of platelet calcium storage and/or extrusion mechanisms. They could facilitate cell stimulation.

Objective: To study membrane viscosity in various rat strains with genetic forms of experimental hypertension., Design: The relationship between blood pressure and membrane dynamics was investigated in erythrocytes from three different rat strains with experimental hypertension, namely two models of salt-induced hypertension (Sabra and Dahl rats) and Lyon hypertensive rats with spontaneous hypertension., Methods: Membrane microviscosity was evaluated by diphenylhexatriene and trimethylamino-diphenylhexatriene fluorescence steady-state anisotropy., Results: There were no significant differences among particular experimental groups in trimethylamino-diphenylhexatriene anisotropy that reflect microviscosity changes at the water-lipid interface of the external membrane leaflet. In contrast, the diphenylhexatriene anisotropy, which is related to the core membrane microviscosity, was significantly reduced in the Dahl salt-sensitive rats (irrespective of salt intake level) and in the Sabra hypertension-prone rats with developed salt hypertension. Erythrocyte membranes of Lyon hypertensive rats also had lower values of diphenylhexatriene anisotropy than the respective normotensive controls but this difference was not statistically significant., Conclusions: Systolic (and often also diastolic) blood pressure correlated negatively with the diphenylhexatriene anisotropy in each of the three strains studied, whereas the trimethylamino-diphenylhexatriene anisotropy of the erythrocyte membranes had no significant relationship to the blood pressure. Further experiments should clarify whether the observed relationship of the diphenylhexatriene anisotropy to blood pressure reflects true pathogenetic mechanisms or is a consequence of haemodynamic changes.

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.

A decrease in platelet 5-HT content linked to partial inhibition of 5-HT uptake has been described in essential hypertension. Transport of 5-HT through platelet membrane is dependent upon transmembranal Na+ and K+ gradients. It is inhibited by Na+, K+-ATPase inhibitors such as ouabain and endogenous digitalis-like compounds isolated from hemodiafiltrate. The activity of such compounds in plasma extracts, measured by inhibition of Na+,K+-ATPase or ouabain binding to human erythrocytes, and platelet 5-HT content were determined in parallel in essential hypertensive patients. Significant negative correlations were observed between these parameters in men, suggesting that high levels of digitalis-like compounds can affect platelet 5-HT content. In addition, in essential hypertensive patients, total plasma cholesterol was inversely related to both platelet 5-HT content (n = 15, r = -0.594, P less than 0.02) and maximal velocity of 5-HT uptake (n = 15, r = -0.717, P less than 0.003). In normotensive control subjects, no variation of platelet 5-HT content with cholesterol was observed. This suggests that the platelet membranes of essential hypertensive patients are more sensitive to increases in plasma cholesterol than those of normotensive subjects.