Increased Ca 2+ influx into platelets induced by thromboxane A 2 analog in patients with ischemic heart disease

We compared platelet aggregation and intracellular free calcium concentrations ([Ca 2+ ] i ) following stimulation with STA 2 , an analog of thromboxane A 2 between patients with ischemic heart disease (IHD) showing significant stenosis in coronary angiograms and controls. In the presence of extracellular calcium, platelet aggregation and intracellular Ca 2+ increase were enhanced by STA 2 stimulation in a dose‐dependent fashion and were higher in the IHD patients than in the controls. However, in the absence of extracellular calcium, no difference in intracellular Ca 2+ increase was observed due to its total dependence on release from intracellular stores. These results suggest that thromboxane A 2 increases platelet intracellular Ca 2+ ‐inducing aggregation, and this increase and aggregation, which is enhanced by thromboxane A 2 in IHD patients, is due to promotion of Ca 2+ influx by thromboxane A 2 . IHD patients appear to have an abnormality in the platelet membrane which may explain such thromboxane A 2 ‐dependent increased permeability to Ca 2+ .