[Effect of thrombin on cytosolic calcium and membrane potential in single human platelets]

Fluo-3 and di-BA-C4 (3) -loaded human platelets were immobilized on a fibrinogen-coated surface and the cytosolic free [Ca2+]i and the membrane potentials were measured in single thrombin-activated platelets by ACAS-570 (Adherent Cell Analysis and Sorting Cytometer). Fluorescence of fluo-3 and di-BA-C4 (3) was low in rest immobilized platelets without obviously repetitive spiking. When the platelets were activated by thrombin, a rapid rise of cytosolic [Ca2+]i and membrane potential was observed. Subsequently, oscillations in [Ca2+]i to an extent of about 500 fluorescent units were observable, whereas the membrane potential remained at the peak level, i.e., the change of [Ca2+]i in no way of accord with that membrane potential. The above results indicate that the thrombin induced membrane depolarization is not due to influx of Ca2+.