RAT DUODENUM NITRERGIC-INDUCED RELAXATIONS ARE, CGMP-INDEPENDENT AND APAMIN-SENSITIVE

The effects of the K+ channel blockers, apamin, tetraethylammonium and 4-aminopyridine, upon the relaxations of the isolated rat proximal du odenum induced by nitrergic nerve ac tivation, nitric oxide (NO), the NO donor 3-morpholinosydnonimine (SIN-1) and Br-cyclic GMP were determ ined. The effects of the guanylate cyclase inhibitors, cystamine and N -methylhydroxylamine, on NO-, SIN-1- and nitrergic nerve-induced respo nses were also investigated. Apamin inhibited nitrergic nerve-, NO-and SIN-1-induced relaxations but did not affect those induced by Br-cGMP . Tetraethylammonium and 4-aminopyridine as well as cystamine and N-me thylhydroxylamine failed to affect the relaxations caused by any of th e agents tested. These findings indicate that, in the rat proximal duo denum, nitrergic nerve activation as well as exogenous nitric oxide ca use relaxation through a cGMP-independent, apamin sensitive mechanism.