EFFECTS OF BIS(2-CHLOROETHYL)SULFIDE ON ATP RECEPTOR-MEDIATED RESPONSES OF THE RAT VAS-DEFERENS - POSSIBLE RELATIONSHIP TO CYTOTOXICITY

Extracellular ATP is a broad-spectrum cytotoxic agent that produces ef fects via cell surface P2 purinoceptors. The ligand-gated P2X purinoce ptor subtype has very high sequence homology with the RP-2 gene, which encodes for apoptosis. The P2X RNA found in rat vas deferens is expre ssed preferentially by apoptotic thymocytes. P2X purinoceptor-mediated phasic (twitch) motor responses of the isolated rat vas deferens to n eurogenic or exogenous ATP were rapidly, specifically and irreversibly potentiated by bis(2-chloroethyl)sulfide (HD 10-100 mu M). Both untre ated and HD-potentiated neurogenic responses were Ca++ dependent, bloc ked in the absence of Ca++ plus 0.1 mM EGTA, by the neuronal Ca++ chan nel blocker omega-conotoxin-MVIIC (3 mu M), by the P2 purinoceptor ant agonist suramin (100 mu M) and by tetrodotoxin (100 nM). HD also poten tiated 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-A TPase in vas deferens or to cause the release of endogenous ATP. Poten tiation of the twitch response to electric field stimulation by HD was attenuated or eliminated in tissues excised from rats previously chal lenged 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 discus sed in relation to apoptosis and necrosis.