Platelet cytosolic calcium concentration, plasma lipids and hypertension.

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 Ca 2+ 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 Ca 2+ 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 [Ca 2+ = 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.