The ATP-Gated P2X₁ Ion Channel Acts as a Positive Regulator of Platelet Responses to Collagen

Summary

ATP is a potent agonist of the P2X₁ ion channel, mediating a rapid, quickly desensitized influx of Ca²⁺. In hirudinized PRP, containing apyrase, the two stable selective P2X₁ agonists, α,β-methylene ATP, and L-β, γ-methylene ATP induced extracellular Ca²⁺-dependent fast and reversible platelet shape change, leading to desensitization of the P2X₁ ion channel. Preincubation with HPLC-purified ADP potently antagonized the subsequent α, β-methylene ATP- and L-β, γ-methylene ATP-evoked platelet shape change. Accordingly, upon heterologous expression of P2X₁ in Xenopus oocytes, HPLC-purified ADP acted as an antagonist of the ATP-induced current, but was inactive itself. Since ATP and ADP are co-released from dense granules during platelet activation, we investigated whether the P2X₁ ion channel is involved in the response of platelets to collagen. We found that platelet shape change and aggregation induced by low concentrations of collagen were strongly inhibited after selective desensitization of P2X₁ with its agonists or by pretreating the platelets with a low concentration of ADP (0.5 μM), that antagonizes the P2X₁ channel without desensitizing the P2Y₁ receptor. Our data suggest that, during collagen-initiated platelet activation, the early secretion of ATP results in the activation of the P2X₁ ion channel, which plays a role as a positive regulator of further platelet responses.

Keywords

Platelet receptor - ATP - collagen - shape change - aggregation

^* considered as first authors.

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