Probes of transmembrane potentials in platelets: changes in cyanine dye fluorescence in response to aggregation stimuli.

A noncovalent fluorescent probe that responded to changes in transmembrane potential was used to study the response of washed human platelets to aggregating agents. Concentration-dependent changes in the fluorescence were observed in response to ADP and to thrombin. No such changes were observed in response to collagen fibrils. Thus there was an indication that platelet membrane potential changed in response to aggregating stimuli, supporting the hypothesis that the mechanisms of platelet aggregation resembled the mechanisms of other systems that show stimulus-response coupling (e.g., muscle, adrenal chromaffin cells). The different responses to specific agents indicate that the agents may trigger platelet aggregation through different mechanisms.