External Na+ is not required for Ca2+ mobilization in platelets stimulated with rattlesnake lectin or alpha-thrombin

The effects of extracellular sodium on platelet aggregation and calcium mobilization in platelets stimulated with either rattlesnake (Crotalus atrox) lectin (RSL) or alpha-thrombin were compared. The absence of extracellular sodium had no effect on platelet aggregation or calcium mobilization in response to all levels of RSL tested. In contrast platelet aggregation was sodium-dependent in response to less than or equal to .2 units/ml alpha-thrombin. Surprisingly, calcium mobilization occurred in platelets treated with a threshold level of alpha-thrombin in the absence of external sodium. Thus sodium-dependent platelet aggregation in response to a low dose of thrombin apparently is not the result of sodium-dependent calcium mobilization.