AJP - Gastrointestinal and Liver Physiology, Vol 249, Issue 2 256-G263, Copyright © 1985 by American Physiological Society
Intracellular electrical activity of muscularis mucosae of the dog stomach
K. G. Morgan, F. Angel, P. F. Schmalz and J. H. Szurszewski
Mechanical and intracellular electrical activity was recorded
simultaneously in vitro from smooth muscle of the muscularis mucosae of the
canine antrum. The intracellularly recorded membrane potential averaged -51
+/- 1.4 mV (mean +/- SE). Spontaneous electrical activity consisted of
spike-shaped potentials that were 20-40 mV in amplitude. The rate of rise
of the spike potential was slow (less than 0.2 V/s) and the half-time
duration was long (0.5-5.0 s). Phasic contractions were often but not
always coupled with spike potentials. Ion substitution studies suggested
that the spike potential had a greater dependence on Na+ than on Ca2+.
Field stimulation of intramural nerves hyperpolarized the membrane
potential and abolished spikes or reduced their amplitude and frequency.
These changes were associated with a reduction in tone and phasic
contractile activity. The response to stimulation of inhibitory nerves was
mimicked by epinephrine, neurotensin, and vasoactive intestinal
polypeptide. The resistance to adrenergic blocking agents ruled out the
possibility of norepinephrine as the transmitter. The tetrodotoxin
sensitivity of the response to neurotensin suggests that neurotensin acts
indirectly through the inhibitory nerves. Mimicry between the action of
applied vasoactive intestinal polypeptide (VIP) and field stimulation
provides support for the hypothesis that VIP may be an inhibitory
neurotransmitter. These studies indicate that smooth muscle in the canine
gastric muscularis mucosae generates spontaneous electrical and mechanical
activity and receives a noncholinergic, nonadrenergic inhibitory
innervation.
