Effects of TMB-8 and diltiazem on platelet activation and cytosolic free Ca2+ concentration in platelets

We investigated the effects of 8-(N, N-diethylamino)-octyl-3, 4, 5-trimethoxybenzoate (TMB-8), intracellular calcium antagonist, and diltiazem, calcium entry blocker, on platelet activation and cytosolic free Ca2+ concentration ([Ca2+]cyt) in platelets.In control, resting [Ca2+]cyt level was 64.6±11.1nM, and 0.5U/ml thrombin-stimulated [Ca2+]cyt was increased to 223.0±32.0nM in the medium containing 0.2mM CaCl2. TMB-8 (0.05mM, 0.1mM, 0.2mM) and diltiazem (0.1mM, 0.2mM, 0.4mM) didn't alter resting [Ca2+]cyt but inhibited thrombin-activated [Ca2+]cyt in a dose-dependent manner. Both drugs also inhibited thrombin-induced platelet aggregation, as well as [Ca2+]cyt. However, they little influenced 14C-serotonin release and 45Ca2+ uptake. There seems to be some particular mode of inhibition, that is, TMB-8 suppresses the rapid phase, and diltiazem suppresses the delayed phase of increase in [Ca2+]cyt stimulatedby thrombin.

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