Basal and stimulated cytosolic platelet calcium in essential hypertension

It was reported that in essential hypertension, basal platelet free cytosolic (Ca)i measured with the fluorescent dye Quin 2, is elevated, but increases normally after thrombin stimulation. These data, were interpreted to suggest that plasma membrane fluxes are altered but the release of internal Ca2+ stores is intact. Previous studies have shown that Quin 2 inhibits Ca2+ release from internal stores following thrombin (T)-stimulation. Thus, we reassessed resting and T-stimulated platelet (Ca)i using the fluorescent dyes Fura 2 or Quin 2 in 11 subjects, 5 controls and 6 hypertensives. Mean basal (Ca)i with Quin 2 in controls was 138 +/- 15 nM vs 114 +/- 11 nM in hypertensives, (NS). By contrast, in the same platelet preparation (Ca)i with Fura 2 was higher in hypertensives than controls, 217 +/- 27 nM vs 120 +/- 4 nM, P less than .05. Blood pressure was correlated to (Ca)i obtained with Fura 2, R = 0.55. Thrombin 0.5 U/ml added to platelets in Ca-free media caused a multiphasic rise in (Ca)i with Fura 2. Although the absolute rise in (Ca)i in controls (592 +/- 104 nm) vs hypertensives (512 +/- 60 nm) did not differ, the % rise was less in hypertensives. Thus, 1) in the same population a higher resting (Ca)i was detected in platelets from essential hypertensives with Fura 2, but not with Quin 2; and 2) Ca2+ release from internal stores is altered in hypertension. Thus, Fura 2 is superior to Quin 2 in evaluating platelet (Ca)i.(ABSTRACT TRUNCATED AT 250 WORDS)