INHIBITORY EFFECT OF TRIMETAZIDINE ON THROMBIN-INDUCED AGGREGATION AND CALCIUM-ENTRY INTO HUMAN PLATELETS

The antiaggregatory properties of trimetazidine were investigated furt her by analyzing its effects on cytosolic calcium and proton concentra tions, well-known regulators of platelet reactivity. Aggregatory respo nses of washed platelets were assessed by turbidometry, and cytosolic Ca2+ concentration ([Ca2+]i) and pH (pHi) were determined by their res pective fluorescent probes: Fura-2 and BCECF. Preincubation with trime tazidine dose-dependently inhibited platelet aggregation induced by 0. 05 U/ml thrombin (p < 0.001). At concentrations less than or equal to 1 mM, trimetazidine did not affect the resting [Ca2+]i value but sligh tly alkalinized the cytosol by 0.05 +/- 0.03 pH units (p < 0.02, n = 1 1). In platelets stimulated by 0.05 U/ml thrombin, 0.1 mM trimetazidin e did not modify pHi variations but decreased [Ca2+]i variations (p < 0.003, n = 16), blunting by 28 +/- 6% the transient peak of [Ca2+]i (p < 0.006) and decreasing by 6 +/- 2% the equilibrium value (p < 0.005) . These inhibitory effects were inversely dependent on thrombin concen trations (p < 0.004, n = 21) and were abolished in the virtual absence of external Ca2+. Trimetazidine therefore attenuates the Ca2+ influx evoked by thrombin, thereby limiting Ca2+ accumulation in stimulated p latelets. Such a protective effect may participate in the antiaggregat ory properties of trimetazidine.