Changes in Cytoplasmic pH and in Membrane Potential in Thrombin-Stimulated Human Platelets

Abstract

The response of human platelets to stimulation by a specific aggregant such as thrombin has been postulated to proceed sequentially via induction of response at the membrane, followed by execution of shape change, secretion and aggregation of the platelets. The platelet response includes a depolarization of the membrane which starts within < 5 s and is thrombin-dose-dependent up to 4.5 nM .alpha.-thrombin. This depolarization may be measured by the distribution of either a fluorescent or a tritium-labeled lipophilic cation. Techniques for intracellular pH measures were adapted for use on the human platelet. Stimulation with thrombin induced a rapid change in the platelet transmembrane pH gradient as measured using either a weak base or a fluorescein derivative as a probe. The pH gradient underwent a time-dependent and thrombin-dose-dependent change which parallels that exhibited by the membrane potential and by serotonin secretion.