Abstract
The gastric emptying is regulated by the coordination of contraction and relaxation in antrum, sphincter and duodenum. The role of purinoceptors and nitric oxide (NO) in the regulation of neurotransmission in the gastric emptying remains unclear. We investigated KCl- and ATP-induced contractile responses in antrum, sphincter and duodenum isolated from rats, and distribution of P2X receptors in these three regions. Sodium nitroprusside, and the nicotinic agonist dimethylphenylpiperazinium iodide caused relaxation in sphincter. ATP caused contraction followed by relaxation in sphincter. Lower (5-20 mM) KCl caused relaxation in sphincter and duodenum but not in antrum, and these relaxations were inhibited by N(G)-nitro-L-arginine methyl ester. NO synthase activity was recognized in sphincter and duodenum. Major expression of P2 purinoceptor was P2X4, and minor expression was P2X6 in these three regions. The P2Y2 subtype was expressed strongly in antrum , less in sphincter and least in duodenum. Amount of P2Y2 receptor expression on these three regions may be associated with loss of contractile activity. The content of ATP was 15 times more in antrum than that in duodenum. Distribution of P2 purinoceptors and nucletides metabolism may be associated with a shift in contractile activity from contraction to relaxation. The phenotype change of P2 receptors in these three regions is associated with weakening of the ATP-induced contraction upon purinoceptor activation and may be a causal factor in the gastric emptying. [J Physiol Sci. 2007;57 Suppl:S241]
