title: Mechanical and electrical responses modulated by excitation of inhibitory nerves during stimulation with high-potassium solutions in circular smooth muscle of the rabbit rectum.
abstract: The properties of the mechanical responses produced by solutions containing high concentrations of potassium ion (high-K solution, [K(+)](o) = 9-27 mM) were investigated in circular smooth muscle preparations isolated from the rabbit rectum. Isometric recording of mechanical responses of the muscle revealed spontaneous contractions, which successively decreased and finally disappeared in most preparations. Stimulation of the smooth muscle with high-K solutions elicited an increase in both amplitude and frequency of twitch contractions (sustained component), with about a 2 min delay in the beginning (initial inhibition), and a transient large contraction shortly after the cessation of stimulation (after contraction). Transmural nerve stimulation (TNS) with electrical pulses for 1 min at 1 Hz frequency produced a sustained inhibition, but a transient contraction followed after termination of TNS. In the presence of tetrodotoxin (TTX), the TNS-induced responses were abolished, while a high-K solution elicited increased twitch contractions with a short delay and abolished the after contraction. Suramin produced effects similar to TTX on the responses produced by high-K solutions or TNS, but this was not the case for atropine, guanethidine or N(omega)-nitro-L-arginine (L-NA). Recording membrane potentials with microelectrodes revealed that TNS evoked an inhibitory junction potential (i.j.p.) which was non-adrenergic, non-cholinergic and non-nitrergic in nature. High-K solutions elicited a tri-phasic change in the membrane potential; an initial hyperpolarization, followed by a sustained depolarization and finally a transient depolarization on cessation of high-K stimulation. TTX or suramin inhibited the i.j.p.s and altered the tri-phasic change in the membrane potential produced by a high-K solution to a mono-phasic depolarization. No significant modulation of electrical responses of the membrane induced by TNS or high-K solution was elicited by atropine, guanethidine or L-NA. The results indicated that the circular smooth muscle of the rabbit rectum is innervated by inhibitory nerves, and that stimulation with high-K solutions caused inhibitory neuronal modulation of both electrical and mechanical responses of the smooth muscle, in a suramin-sensitive way.
authors.affiliation: Department of Physiology, Nagoya City University Medical School, Mizuho-ku, Nagoya, Japan.
authors.forename: Kousuke
authors.initials: K
authors.lastname: Kato
authors.forename: Yoshihiko
authors.initials: Y
authors.lastname: Kito
authors.forename: Hikaru
authors.initials: H
authors.lastname: Suzuki
mesh_terms: D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology; D001285:Atropine / Q000494:pharmacology; D001993:Bronchodilator Agents / Q000494:pharmacology; D004558:Electric Stimulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006145:Guanethidine / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects* / Q000502:physiology; D009130:Muscle, Smooth / Q000502:physiology*; D009433:Neural Inhibition / Q000502:physiology; D009469:Neuromuscular Junction / Q000187:drug effects / Q000502:physiology*; D019335:Nitroarginine / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology*; D011817:Rabbits; D012007:Rectum / Q000294:innervation / Q000502:physiology*; D026941:Sodium Channel Blockers / Q000494:pharmacology; D013268:Stimulation, Chemical; D013779:Tetrodotoxin / Q000494:pharmacology
chemical_list: D000959:Antihypertensive Agents; D001993:Bronchodilator Agents; D004791:Enzyme Inhibitors; D026941:Sodium Channel Blockers; D019335:Nitroarginine; D013779:Tetrodotoxin; D001285:Atropine; D011188:Potassium; D006145:Guanethidine