Diverse effects of ethanol on Ca entry and subsequent aggregation of platelets

Although alcohol is known to inhibit platelet aggregation, and transplasmalemmal Ca²⁺ entry is profoundly involved in platelet aggregation, there has been limited knowledge about the relationship between alcohol and Ca²⁺ entry. The purpose of this study was to determine whether and how ethanol in vitro affects Ca²⁺ entry through different pathways and the subsequent aggregation of platelets. Thapsigargin, 1-oleoyl-2-acetyl-sn-glycerol (OAG), and thrombin were used to stimulate human platelets. Ca²⁺ entry and the subsequent aggregatory responses of platelets were measured by spectrofluorometry using fura-2/AM as an indicator and the light transmission method, respectively. Thapsigargin-induced Ca²⁺ entry and the following platelet aggregation were significantly inhibited by ethanol at concentrations of 0.5% or more. OAG-induced Ca²⁺ entry was significantly augmented by ethanol at concentrations of 0.5% or more, whereas platelet aggregation by OAG was significantly inhibited by ethanol at concentrations of 0.5 % or more. Thrombin-induced Ca²⁺ entry was not significantly affected by ethanol up to 2%, whereas platelet aggregation by thrombin was markedly inhibited by ethanol at concentrations of 0.5% or more. Thrombin-induced Ca²⁺ entry in the presence of SKF-96365 was augmented by pretreatment with ethanol. Ethanol in vitro showed diverse effects on the different Ca²⁺ entry pathways of platelets, whereas aggregatory responses induced by activation of the different Ca²⁺ entry pathways of platelets were all inhibited by ethanol. These results suggest that ethanol inhibits platelet aggregation mainly via a mechanism(s) other than transplasmalemmal Ca²⁺ entry.