Excitatory actions of motilin on myenteric neurons of the guinea-pig small intestine.
Motilin is considered as a key factor in controlling interdigestive migrating contractions. The present electrophysiological experiments were performed in vitro to examine actions of motilin on myenteric neurons of guinea-pigs after 18-h fasting period. Superfusion of motilin depolarized both S and AH neurons; the lowest effective concentration was 10 nM, and motilin depolarization was observed in 9 of 23 S neurons and in 5 of 25 AH neurons. The motilin depolarizations were associated with an increase in neuronal input resistance. The motilin responses were preserved in Ca2+ free/high Mg2+ solution in which no Ca2+ dependent synaptic transmission occurred. The reversal potential of the motilin responses was estimated about -95 mV, close to the equilibrium potential for K+. Furthermore, muscarinic depolarizations were blocked during the motilin responses. All of these indicated that motilin directly excited myenteric neurons mainly by inactivating K+ channels. It is concluded that motilin might modulate neuronal excitability of the myenteric plexus, leading to the control of interdigestive migrating contractions.
Katayama
Yoshifumi
Y
Department of Autonomic Physiology, Medical Research Institute, Tokyo Medical and Dental University, 2-3-10 Kandasurugadai, Chiyoda-ku, Tokyo, 101-0062, Japan. kataauto@tmd.ac.jp
Ooishi
Kiyotoshi
K
Hirai
Keiji
K
Homma
Tomoo
T
Noda
Yumi
Y
D000109:Acetylcholine / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D005765:Gastrointestinal Agents / Q000494:pharmacology*; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007421:Intestine, Small / Q000033:anatomy & histology*; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D009037:Motilin / Q000494:pharmacology*; D009197:Myenteric Plexus / Q000166:cytology*; D009433:Neural Inhibition / Q000187:drug effects; D009474:Neurons / Q000187:drug effects* / Q000502:physiology; D011188:Potassium / Q000494:pharmacology; D014665:Vasodilator Agents / Q000494:pharmacology
D005765:Gastrointestinal Agents; D014665:Vasodilator Agents; D009037:Motilin; D008274:Magnesium; D000109:Acetylcholine; D011188:Potassium