A major role for P2X(I) receptors in the early collagen-evoked intracellular Ca2+ responses of human platelets

In the platelet, ATP-gated P2X1 receptors have been reported to amplify functional responses to collagen,however the relative importance of early Ca2+ mobilisation events is unknown. We now report that selective desensitisation of P2X1 receptor activity leads to a major reduction in the initial intracellular Ca2+ responses to a wide range of collagen concentrations (0.25–2 µ g ml-1). Peak [Ca2+] i increases were reduced to 8.5 and 55% of control, and the maximum rate of rise was reduced to 12 and 33% of control,at low and high collagen concentrations,respectively. This P2X 1 -dependent acceleration and enhancement of collagen-stimulated Ca2+ responses was not observed in the absence of extracellular Ca2+.These results demonstrate a major role for ATP-gated Ca2+ influx in the early collagen-evoked Ca2+ signals and can at least partly explain the important contribution of P2X1 receptors to arterial thrombosis.