Abstract

Extracellular ATP is a broad-spectrum cytotoxic agent that produces effects via cell surface P2 purinoceptors. The ligand-gated P2X purinoceptor subtype has very high sequence homology with theRP-2 gene, which encodes for apoptosis. The P2X RNA found in rat vas deferens is expressed preferentially by apoptotic thymocytes. P2X purinoceptor-mediated phasic (twitch) motor responses of the isolated rat vas deferens to neurogenic or exogenous ATP were rapidly, specifically and irreversibly potentiated by bis(2-chloroethyl)sulfide (HD 10-100 μM). Both untreated and HD-potentiated neurogenic responses were Ca⁺⁺ dependent, blocked in the absence of Ca⁺⁺ plus 0.1 mM EGTA, by the neuronal Ca⁺⁺channel blocker ω-conotoxin-MVIIC (3 μM), by the P2 purinoceptor antagonist suramin (100 μM) and by tetrodotoxin (100 nM). HD also potentiated the effects of ATP on isolated guinea pig taenia caecum, where the nucleotide acts at G protein-coupled P2Y purinoceptor subtypes to cause relaxation. HD failed to inhibit the metabolism of ATP by ecto-ATPase in vas deferens or to cause the release of endogenous ATP. Potentiation of the twitch response to electric field stimulation by HD was attenuated or eliminated in tissues excised from rats previously challenged with topically applied HD, suggesting that HD absorbed into the systemic circulation had already effected maximal potentiation of ATP responses before in vitro testing. The physiological consequences of HD-induced potentiation of the extracellular actions of ATP are discussed in relation to apoptosis and necrosis.