The ATP-Gated P2X1 Ion Channel Acts as a Positive Regulator of Platelet Responses to Collagen
Cecile Oury(1), *, Emese Toth-Zsamboki(1), *, Chantal Thys(1), Jan Tytgat(2), Jos Vermylen(1), Marc F. Hoylaerts(1)
(1)Center for Molecular and Vascular Biology, University of Leuven, Leuven, Belgium, (2)Laboratory of Toxicology, University of Leuven, Belgium
Summary ATP is a potent agonist of the P2X1 ion channel, mediating a rapid,quickly desensitized influx of Ca2+. In hirudinized PRP, containingapyrase, the two stable selective P2X1 agonists, α,β-methylene ATP,and L-β,γ-methylene ATP induced extracellular Ca2+-dependent fastand reversible platelet shape change, leading to desensitization of theP2X1 ion channel. Preincubation with HPLC-purified ADP potentlyantagonized the subsequent α,β-methylene ATP- and L-β,γ-methyleneATP-evoked platelet shape change. Accordingly, upon heterologousexpression of P2X1 in Xenopus oocytes, HPLC-purified ADP acted asan antagonist of the ATP-induced current, but was inactive itself. SinceATP and ADP are co-released from dense granules during plateletactivation, we investigated whether the P2X1 ion channel is involved inthe response of platelets to collagen. We found that platelet shapechange and aggregation induced by low concentrations of collagenwere strongly inhibited after selective desensitization of P2X1 with itsagonists or by pretreating the platelets with a low concentration of ADP(0.5 µM), that antagonizes the P2X1 channel without desensitizing theP2Y1 receptor. Our data suggest that, during collagen-initiated plateletactivation, the early secretion of ATP results in the activation of theP2X1 ion channel, which plays a role as a positive regulator of furtherplatelet responses.