Membrane potential of stored platelets and its effect on platelet functions.

Relationships among intracellular Ca2+ level, membrane potential in resting state and platelet functions were examined. Membrane potential of platelets was increased (hyperpolarized) during storage and decreased (depolarized) by 37 degrees C incubation with plasma after storage. The degree of depolarization was greater in fresh plasma than in stored plasma. Changes of platelet functions were reverse with the membrane potential change. Aggregation induced by ADP or collagen was enhanced by depolarization with increasing extracellular [K+]. Shrinkage ratio (hypotonic shock response) of stored platelet which were hyperpolarizing, exhibited optimal value when the membrane potential was slightly depolarized. Intracellular [Ca2+] was not affected by the extracellular [K+]. These results suggest that platelet sensitivity is controlled by the membrane potential in resting state.