Evidence for the involvement of P2 -purinoceptors in the cholinergic contraction of the guinea-pig ileum

Abstract

In the isolated ileum of the guinea-pig the P2-purinoceptor antagonists PPADS and suramin: (a) strongly inhibited the cholinergic contractile effect of alpha,beta-methylene ATP, (b) did not influence contractions evoked by exogenous acetylcholine (ACh) but, (c) moderately (by about 30%) inhibited cholinergic contractions due to electrical field stimulation (EFS), in a non-additive manner. These results suggest that an endogenous ligand that stimulates P2-purinoceptors (possibly ATP) is involved in the contractile effect of EFS, as a positive modulator of ACh release.