Effects of of circular gastric 5-hydroxytryptamine on smooth muscle isolated antrum electrical fromthe responses-- gulnea-plg

The effects of 5-hydroxytryptarnine (5-HT) on electrical responses of the membrane were investigated in circular smooth muscle isolated from the guinea-pig stomach antrum. Small segment of circular muscle tissue produced a periodical generation of slow potentials at frequency of O,1-2 cycles min", during random generation of unitary potentials, Application of 5-HT (10-7-10-5 M) hyperpolarized the membrane and either increased or decreased the frequency of slow potentials, both with associated increase in amplitude of slow potential, These effects of 5-HT were abolished by methysergide. NMnitro-I.arginine (L-NA) increased the frequency of spontaneously generated slow potentials and also increased the frequency of slow potentials generatecl during stimulation with 5-HT, suggesting an involvement of the increased production of nitric oxide (NO) by 5-HT. Atropine did not alter spontaneous and 5-HT-incluced electrical responses. The hyperpolarization produced by 5-HT was associated with a decrease in input resistance and time constant of the membrane. The amplitude of the 5H'ILinduced hyperpolarization was increased in low [K']. solution and decreased in high [K']o solution or in the presence of glybenclamide, suggesting that the hyperpolarization was produced by activation of AI"P-sensitive K-channels. The increase in amplitude of slow potentials by 5-HT may be secondary due to hyperpolarization f the membrane. [[he inhibition by 5-HT of the frequency of slow potentials may be partly due to the increased release of NO, however the mechanism by which dual effects of 5-HT on the frequency of slow potentials remains unsolved.