Vol. 290, Issue 3, 1175-1181, September 1999

Contribution of Nitric Oxide to the Presynaptic Inhibition by Endothelin ET_B Receptor of the Canine Stellate Ganglionic Transmission

Katsuhiro Yamada, Kazushi Kushiku, Hiromi Yamada, Takeshi Katsuragi, Tatsuo Furukawa, Hidenori Noguchi and Nobufumi Ono

Department of Pharmacology, School of Medicine (K.Y., K.K., H.Y., T.K., T.F.) and Medicinal Informatics and Research Units (H.N., N.O.), Faculty of Pharmaceutical Sciences, Fukuoka University, Fukuoka, Japan

We previously reported that endothelin (ET) 3 inhibited presynaptically the dog stellate ganglionic transmission. Here, we report the investigation of the possible involvement of nitric oxide pathway in the endothelin-induced inhibition of the ganglionic transmission. The amount of acetylcholine released by preganglionic stimulation for 10 min was concentration-dependently inhibited after exposure to ET-3 (10⁹-10⁶ M) or IRL-1620, endothelin ET_B receptor agonist (10⁸-10⁵ M). The inhibition was antagonized by pretreatment with a nonselective endothelin receptors antagonist (bosentan) and an ET_B receptor antagonist (BQ-788) or a neuronal nitric oxide synthase inhibitor, 3-bromo-7-nitroindazole, but was not inhibited by a selective ET_A receptor antagonist, BQ-123. The reduction induced by ET-3 was also antagonized by treatment with a selective inhibitor of soluble guanylyl cyclase, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one. In addition, similar reductions were also mimicked by exposure to cGMP analog, 8-bromoguanosine-3,5-cyclic monophosphate and nitric oxide donor, S-nitroso-N-acetylpenicillamine. Exposure to ET-3 or IRL-1620 for a 30-min period increased the levels of total nitric oxide (NO), nitrite plus nitrate NO_x concentration in the incubation medium, with the increase in NO_x also being antagonized by BQ-788 at the same concentration. The ET-3-induced increase in NO_x was antagonized by treatment with the same concentration of 3-bromo-7-nitroindazole or a selective inhibitor of receptor-mediated Ca²⁺ entry, 1-[b-[3-(4-methoxyphenyl) propoxy]-4-methoxyphenethyl]-1H-imidazole (10⁵ M), and with a calmodulin antagonist, N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide. These results indicate that ET_B receptor activation inhibits the sympathetic ganglionic transmission via reducing acetylcholine release from presynaptic nerve terminals, although this inhibition also seems to involve the ET_B receptor-operated Ca²⁺-calmodulin-dependent activation of endogenous nitric oxide production.