Effects of 5-hydroxytryptamine on electrical responses of circular smooth muscle isolated from the guinea-pig gastric antrum.
The effects of 5-hydroxytryptamine (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 0.1-2 cycles min(-1), 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. N(omega)-nitro-L-arginine (L-NA) increased the frequency of spontaneously generated slow potentials and also increased the frequency of slow potentials generated 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-induced 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 5-HT-induced hyperpolarization was increased in low [K(+)](o) solution and decreased in high [K(+)](o) solution or in the presence of glybenclamide, suggesting that the hyperpolarization was produced by activation of ATP-sensitive K-channels. The increase in amplitude of slow potentials by 5-HT may be secondary due to hyperpolarization of the membrane. The 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.
Kim
Young Chul
YC
Department of Physiology, Chungbuk National University, College of Medicine, Cheongju, Chungbuk, Korea.
Hayase
Masa
M
Nakamura
Eri
E
Kito
Yoshihiko
Y
Suzuki
Hikaru
H
D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology; D001285:Atropine / Q000494:pharmacology; D004594:Electrophysiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005905:Glyburide / Q000494:pharmacology; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008784:Methysergide / Q000494:pharmacology; D009130:Muscle, Smooth / Q000187:drug effects* / Q000502:physiology*; D009197:Myenteric Plexus / Q000187:drug effects / Q000502:physiology; D019335:Nitroarginine / Q000494:pharmacology; D010276:Parasympatholytics / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D011706:Pyloric Antrum / Q000187:drug effects* / Q000294:innervation / Q000502:physiology; D012701:Serotonin / Q000494:pharmacology*; D018490:Serotonin Agents / Q000494:pharmacology*; D012702:Serotonin Antagonists / Q000494:pharmacology
D000889:Anti-Arrhythmia Agents; D004791:Enzyme Inhibitors; D010276:Parasympatholytics; D018490:Serotonin Agents; D012702:Serotonin Antagonists; D019335:Nitroarginine; D012701:Serotonin; D001285:Atropine; D011188:Potassium; D005905:Glyburide; D008784:Methysergide