P2 purinoceptors account for the non-nitrergic NANC relaxation in the rat ileum

The transmitters involved in the non-nitrergic component of the non-adrenergic, non-cholinergic (NANC) inhibitory response of the rat small intestinal longitudinal muscle to electrical field stimulation of its nerves is a matter of controversy. The present study is the first one to utilise a combination of a nitric oxide synthase inhibitor and a P-2 purinoceptor antagonist for studying this response. We found that the P-2 purinoceptor antagonist pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS; 5x10(-5) M) abolished the non-nitrergic NANC relaxation to electrical field stimulation (10 Hz). PPADS alone provided a significant, moderate inhibitory action. PPADS specifically inhibited relaxations due to exogenous adenosine 5'-triphosphate (ATP) or alpha,beta-methylene ATP. The guanylate cyclase blocker 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ; 10(-6)p M) did not add to the inhibitory action of N-G-nitro-L-arginine on field stimulation-induced relaxation. ODQ abolished the relaxant effect of the nitric oxide donors nitroglycerin or sodium nitroprusside. These data indicate that: (1) nitric oxide and ATP fully account for the field stimulation-induced relaxation in the rat ileal strip under the experimental conditions of this study, and (2) no ODQ-sensitive guanylate cyclase-mediated mechanism is involved in the non-nitrergic component of the NANC relaxation.