Alterations in The Trans-Membrane Potential of Human Blood Platelets in Response to Aggregating Stimuliow

Abstract

It has been suggested that the mechanism of response of platelets to aggregating stimuli is analogous to the stimulus-response coupling mechanisms of muscle and secretory cells. Because the coupling mechanisms of both types of systems involve changes in the trans-membrane potential of the stimulated cell, we have examined the membrane potential of human platelets to determine if the potential changes in response to aggregating agents. The membrane potential of gel-filtered platelets was monitored using a fluorescent cyanine dye. Aggregation was prevented to minimize artifacts due to changes in light scattering. The effects of ADP, thrombin, and collagen on the potential were examined. In response to ADP, the membrane rapidly became more negatively polarized. The response was concentration dependent, the minimum response occurring with 3x10-5M ADP. The response to thrombin was more complex. Low concentrations (0.01 U/ml) produced a change similar to that caused by ADP. Higher concentration (1–10 U/ml) led to a rapid decrease in the polarization of the membrane. When pre-formed collagen fibrils were added, in the presence of creatine Phosphokinase to destroy released ADP, no changein the potential was observed.Thus the platelet membrane potential changes in response to aggregating stimuli, supporting the hypothesis that stimulus of platelet aggregation is analogous to other stimulus-response coupling mechanisms. The change in potential is not a necessary step in the coupling mechanism. The different responses to specific agents indicate that the agents may trigger aggregation through different mechanisms.