Effects of goniopora toxin on non‐adrenergic, non‐cholinergic response and purine nucleotide release in guinea‐pig taenia coli

Abstract

1. Effects of goniopora toxin (GPT) on non-adrenergic, non-cholinergic inhibitory responses were examined in isolated guinea-pig taenia coli and the transmission mechanism was analysed.2. GPT (20-50 nM) gradually augmented the relaxation and rebound contraction induced by electrical transmural stimulation in the presence of guanethidine and atropine. These effects were abolished by tetrodotoxin.3. The resting tension and the response to exogenously applied ATP were little affected by GPT.4. The action potentials and the electrotonic potentials recorded by a double sucrose-gap method were little affected by GPT.5. These results indicate that the augmentation is elicited by a direct action of GPT on the non-adrenergic, non-cholinergic neurones, rather than on the smooth muscles per se.6. GPT augmented the amplitude of the inhibitory junction potential (i.j.p.) recorded in the presence of guanethidine and atropine. GPT also enhanced the (3)H efflux in response to electrical transmural stimulation of preparations pre-loaded with [(3)H] adenosine. Tetrodotoxin markedly inhibited or abolished the i.j.p. and (3)H efflux.7. These results would suggest that augmentation of the non-adrenergic, non-cholinergic responses is due to increased transmitter release from the nerve. Under conditions in which the transmitter release was augmented, the non-adrenergic, non-cholinergic response showed an essentially similar pattern to that obtained under normal conditions; therefore the inhibitory response is probably due to a putative transmitter, possibly ATP or a related nucleotide.