ATP-stimulated P2X(1) and ADP-stimulated P2Y(1) receptors play important roles in platelet activation. An increase in intracellular Ca2+ represents a key signalling event Coupled to both of these receptors, mediated via direct gating of Ca2+-permeable channels in the case of P2X(1) and phospholipase-C-dependent Ca2+ mobilisation for P2Y(1). We show that disruption of cholesterol-rich membrane lipid rafts reduces P2X(1) receptor-mediated calcium increases by similar to 80%, while P2Y(1) receptor-dependent Ca2+ release is unaffected. In contrast to artery, vas deferens, bladder smooth muscle, and recombinant expression in cell lines, where P2X(1) receptors show almost exclusive association with lipid rafts, only similar to 20% of platelet P2X(1) receptors are co-expressed with the lipid raft marker flotillin-2. We conclude that lipid rafts play a significant role in the regulation of P2X(1) but not P2Y(1) receptors in human platelets and that a reserve of non-functional P2X(1) receptors may exist. (c) 2006 Elsevier Inc. All rights reserved.