Pentagastrin potentiates nonadrenergic inhibitory neuromuscular transmission in orad stomach of the dog.

Mechanical and intracellular electrical activities were recorded separately from circular muscle of the orad corpus of the canine stomach. In normal Krebs solution, transmural electrical nerve stimulation produced excitatory and inhibitory responses. The excitatory response was blocked by atropine; the inhibitory response was unaffected by phentolamine or propranolol alone or in combination. Both responses were blocked by tetrodotoxin. In the presence of pentagastrin, the inhibitory response to electrical nerve stimulation was potentiated in a dose-dependent manner. The threshold concentration for this potentiating effect was 3 X 10(-11) M. Intracellular recordings showed that hyperpolarization of the resting membrane potential in response to inhibitory nerve stimulation was greater in the presence of pentagastrin than in its absence. These data suggest that, in addition to a direct stimulatory effect on the muscle, pentagastrin also potentiates the effect of ongoing activity of intramural inhibitory nerves. This latter effect is only apparent when the inhibitory neural network is active. Thus, the in vivo effect of pentagastrin on motor activity of the corpus will depend on the degree of ongoing activity of intramural inhibitory nerves.