VIP and acetylcholine: neurotransmitters in esophageal circular smooth muscle.
Vasoactive intestinal polypeptide (VIP) and acetylcholine were evaluated as possible inhibitory and excitatory neurotransmitters in the cat esophageal circular smooth muscle. Circular muscle strips 2 mm in thickness were obtained from 1 to 3.4 cm above the lower esophageal sphincter and tested in vitro. Muscle strips contracted with bethanechol (10(-5) M) were relaxed by electrical stimulation (0.5-5 Hz) and by VIP (10(-8)-10(-6) M). Relaxation induced by electrical stimulation was blocked by tetrodotoxin, whereas VIP-induced relaxation was not affected. Highly specific VIP antiserum (5%) antagonized both VIP and electrically induced relaxation, and the antagonism was eliminated when the antiserum was neutralized with VIP (10(-6.5) M). Dopamine (10(-4) M) reduced the relaxation induced both by exogenous VIP and by electrical stimulation but did not affect the relaxation caused by sodium nitroprusside (10(-8)-10(-5) M). In untreated strips, physostigmine (10(-10)-10(-8) M) enhanced the off contraction in response to electrical stimulation, whereas atropine caused a dose-dependent reduction with complete abolition at 10(-4) M. These data suggest that in the esophagus inhibition and excitation are mediated by distinct mechanisms: VIP mediates inhibition and acetylcholine is responsible for the off contraction in response to electrical stimulation.
Behar
J
J
Department of Medicine, Rhode Island Hospital, Providence.
Guenard
V
V
Walsh
J H
JH
Biancani
P
P
D000109:Acetylcholine / Q000494:pharmacology* / Q000502:physiology; D000818:Animals; D002415:Cats; D004298:Dopamine / Q000494:pharmacology; D004558:Electric Stimulation; D004947:Esophagus / Q000187:drug effects / Q000294:innervation / Q000502:physiology; D005260:Female; D007106:Immune Sera / Q000276:immunology; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000294:innervation / Q000502:physiology*; D018377:Neurotransmitter Agents / Q000494:pharmacology* / Q000502:physiology; D014660:Vasoactive Intestinal Peptide / Q000276:immunology / Q000494:pharmacology* / Q000502:physiology
D007106:Immune Sera; D018377:Neurotransmitter Agents; D014660:Vasoactive Intestinal Peptide; D000109:Acetylcholine; D004298:Dopamine