The in vitro effects of ethanol on intracellular Ca2+ homeostasis and tyrosine phosphorylation have been investigated in human platelets in order to clarify the cellular mechanisms underlying its described anti-aggregant effects. Ethanol (1-50 mM) reduced, in a dose-dependent manner, the rate and amplitude of aggregation and attenuated the phosphotyrosine content both induced by 0.1 U/ml of the physiological ligand, thrombin. Thrombin-induced Ca2+ entry to the cytosol was significantly reduced, and capacitative Ca2+ entry (CCE) significantly altered, by 50 mM ethanol, so that ethanol reduces CCE mediated by depletion of the 2,5-di-(tert-butyl)-1,4-hydroquinone (TBHQ)-sensitive store but enhances CCE induced by the TBHQ-in sensitive pool. In conclusion, we provide considerable evidence that ethanol reduces thrombin-induced aggregation, which is likely a result of a significant inhibition of Ca2+ entry, as well as a reduction in the activity of protein tyrosine kinases. (c) 2006 Elsevier Inc. All rights reserved.