Electrical and mechanical activities of the longitudinal muscle of the dog antrum were recorded with the double sucrose gap technique. The muscle exhibited spontaneous action potentials which consisted of a spike like potential which, after a brief and partial repolarization, was followed by a negative going, plateau type potential. In 97% of the preparations, no tension changes were produced by spontaneous action potentials. Tetrodotoxin, atropine, alpha and beta adrenoceptor antagonists, and H1 and H2 receptor blocking agents had no effect on the action potential. It was concluded that the action potential was myogenic in origin. The mean frequency of the action potential at 37±0.5°C was 1.0/min ± 0.06 (S.E. of mean, n = 92) and the mean duration 7.1 ± 0.2 sec (S.E. of mean, n = 11). Steady depolarizing current increased whereas hyperpolarizing current decreased the frequency of the action potential. Length tension relations were studied. In twelve strips, the average resting, passive, tension at L0 was 570 mg. The active force of isometric contraction produced by acetylcholine increased with strip length up to a maximum, then decreased with further increases in length. There were no mechanical responses to pentagastrin. Pentagastrin had two sites of action. On smooth muscle, it increased the frequency of the action potential in a dose dependent fashion. Threshold concentrations ranged from 2 x 10-14 to 10-11 M. The ED50 was 2 x 10-10 M. The maximum response, 5.4/min, was reached at 10-8 M. Pentagastrin also released acetylcholine from intramural cholinergic nerves. Pentagastrin reduced the amplitude and duration of the action potential.
|Original language||English (US)|
|Number of pages||27|
|Journal||Journal of Physiology|
|State||Published - 1975|
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