Effect of metabolic inhibitors on thrombin-induced membrane potential changes in washed human platelets

Platelet stimulation by thrombin or other agonists is influenced by the metabolic status of the platelet, i.e., by the available supply of metabolic ATP. We have shown earlier that such stimulation by thrombin is accompanied by a dose-dependent depolarization of the platelet transmembrane potential and by a decrease in the transmembrane pH gradient. We have now studied the effect of metabolic inhibitors on the membrane potential changes as assessed with the fluorescent cation 3, 3′-dipropylthiodicarbocyanine. Preincubation of platelets with either 2-deoxy-D-glucose or antimycin A leads to a partial depolarization of the resting platelet's membrane. These pre-incubated platelets then exhibit a decreased membrane potential change upon α-thrombin stimulation.It is known that the platelet continuously replenishes its glycogen. The availability of such energy stores may be responsible for the restoration of approximately 20% of the thrombin response which we have observed after 3 hours of incubation with antimycin A. The intracellular glycogen does not appear to play a major role in the early platelet response to thrombin which is unimpaired 30 minutes after the completion of gel-filtration, the time at which the intracellular glycogen levels are at their lowest. These studies indicate that the thrombin-induced platelet membrane potential change, like other steps in platelet activation, depends upon maintenance of continuous metabolic function.