Effects of ATP, its related nucleotides and VIP on the inhibitory potentials in the smooth muscle cells of the guinea-pig duodenum.

Non-adrenergic inhibitory potentials (i.p.'s) were recorded from the smooth muscle cells of the guinea-pig duodenum following field stimulation. ATP, ADP and AMP increased the membrane potential of the cell and decreased the amplitude and the rate of hyperpolarization of the i.p. The amplitudes of the maximum hyperpolarization due to a repeated stimulation and the post-stimulus depolarization were reduced by ATP and AMP. Methylxanthine could not inhibit the i.p. while apamin reversibly decreased the amplitudes of the i.p. and the post-stimulus depolarization. The latency and the time to peak were prolonged by apamin. Biphasic effect of quinidine on the i.p. was obtained. The amplitude and the rate of hyperpolarization of the i.p. were decreased at 10-4 g/ml of quinidine. The amplitudes of the maximum hyperpolarization by repetitive stimulation and the post-stimulus depolarization were decreased by quinidine. The membrane potential of the cell was not affected by VIP. The amplitude and the other parameters of the i.p. were not changed in the used concentration of VIP. Trypsin reduced the membrane potential of the cell but not changed the parameters of the i.p. The membrane was slightly depolarized by the treatment with papain while no significant changes on the i.p. were observed in papain. The obtained results suggest that ATP, its related substances and VIP do not contribute to the non-adrenergic inhibitory neurotransmission.