Effects of pentagastrin, G₁₇, and G₃₄ on the electrical and mechanical activities of canine antral smooth muscle

Intracellular microelectrode technique and standard organ bath technique were used to investigate the effects of pentagastrin, G₁₇, and G₃₄ on the electrical and mechanical activities of canine antral circular muscle. All three molecular forms increased the amplitude and duration of the plateau of the gastric action potential and the frequency of spontaneous action potentials. They also increased the amplitude and frequency of spontaneous contractions. G₁₇ was equal to or less potent than pentagastrin in all of its actions on this tissue. G₃₄ had an equal or greater activity than G₁₇. The electrical studies indicate that G₁₇ is active in this tissue in a physiological range of concentrations. The ed₅₀ for the effect of G₁₇ to increase the amplitude of the plateau potential is less than that for the effect of G₁₇ on gastric secretion, indicating that this is a physiological action of gastrin. Atropine studies indicate that only part of the in vitro inotropic action of gastrin is caused by the release of acetylcholine from nerve terminals, but that the chronotropic action is attributable to a direct effect on the smooth muscle membrane.