The neurotransmitters mediating relaxation of lower esophageal sphincter (LES) were studied using circular LES strips from adult pigs in organ baths. LES relaxation by sodium nitroprusside (1 nM-3 μM), vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating peptide (PACAP; 1 nM-1 μM), ATP (10 μM-30 mM), and tricarbonyldichlororuthenum dimer (1 μM-1 mM) was unaffected by tetrodotoxin (1 μM) or L-NG-nitroarginine methyl ester (L-NAME; 100 μM). Calcitonin gene-related peptide (CGRP; 1 nM-1 μM) did not affect LES tone. ATP relaxation was blocked by 1 μM apamin and the P2Y1 antagonist MRS 2179 (N6-methyl 2′-deoxyadenosine 3′,5′-bisphosphate; 10 μM). Apamin inhibited PACAP relaxation. VIP and PACAP relaxation was blocked by 10 U/ml α-chymotrypsin. L-NAME (-62.52 ± 13.13%) and 1H-[1,2,4]oxadiazole- [4,3-α]quinoxalin-1-one (ODQ; 10 μM, -67.67 ± 6.80%) similarly inhibited electrical LES relaxation, and apamin blocked non-nitrergic relaxation. Nicotine relaxation (100 μM) was inhibited by L-NAME (-60.37 ± 10.8%) and ODQ (-41.90 ± 7.89%), and apamin also blocked non-nitrergic relaxation. Non-nitrergic and apamin-sensitive LES relaxation by electrical stimulation or nicotine was strongly inhibited by MRS 2179, slightly inhibited by α-chymotrypsin and the P2X1,2,3 receptor antagonist NF 279 (8,8¢-[carbonylbis(imino-4,1-phenylenecarbonylimino-4,1- phenylenecarbonylimino)]bis-1,3,5-naphthalenetrisulfonic acid hexasodium salt; 10 μM), and unaffected by tin protoporphyrin IX (100 μM). Porcine LES relaxation after stimulation of intrinsic inhibitory motor neurons is mediated by two main neuromuscular pathways: nitric oxide through guanylate cyclase signaling and apamin-insensitive mechanisms and by non-nitrergic apamin-sensitive neurotransmission mainly mediated by ATP, ADP, or a related purine acting on P2Y1 receptors and a minor contribution of purinergic P2X1,2,3 receptors and PACAP. Nitrergic and purinergic co-transmitters show parallel effects of similar magnitude without major interplay. Our study shows no role for CGRP and only a minor one for VIP and carbon monoxide in porcine LES relaxation. Copyright © 2006 by The American Society for Pharmacology and Experimental Therapeutics.
|Journal||Journal of Pharmacology and Experimental Therapeutics|
|Publication status||Published - 1 Mar 2006|