Effects of suramin on electrical and mechanical activities in antrum smooth muscle of the guinea-pig stomach

1 The effects of suramin on electrical and mechanical responses produced by adenosine triphosphate (ATP), acetylcholine and transmural nerve stimulati on were observed in antrum smooth muscle isolated from the guinea-pig stoma ch. 2 Suramin (>10(-6) M) inhibited the non-adrenergic non-cholinergic inhibito ry junction potential, with no alteration of the resting membrane potential , slow wave and the ATP-induced responses (hyperpolarization and inhibition of slow waves). 3 The amplitude, but not the frequency, of spontaneous rhythmic contraction was inhibited by suramin (>10(-5) M), with no alteration of electrical res ponses of the membrane. 4 Transmural nerve stimulation elicited cholinergic excitatory and non-adre nergic non-cholinergic inhibitory responses on the spontaneous contraction, and suramin inhibited only the latter. 5 Suramin did not alter the ATP-induced inhibition of spontaneous contracti on. The contractions produced by low concentrations (<10(-7) M), but not hi gh concentrations (10(-6)-10(-5) M), of acetylcholine were inhibited by sur amin. 6 It is concluded that in smooth muscle of the guinea-pig antrum, suramin i nhibits contractions produced spontaneously and by low concentrations of ac etylcholine, with no relation to the electrical responses of the membrane, parallel inhibition by suramin of the electrical and mechanical responses e licited by excitation of non-adrenergic non-cholinergic inhibitory nerves m ay not be causally related to the inhibition of ATP-receptors.