SURAMIN INHIBITS EXCITATORY JUNCTION POTENTIALS IN GUINEA-PIG ISOLATED VAS-DEFERENS

1. Intracellular microelectrode recording techniques were used to investigate the action of the putative P2-purinoceptor antagonist, suramin, on sympathetic neurotransmission in the guinea-pig isolated vas deferens. 2. The resting membrane potential of the control cells was 67.4 +/- 0.7 mV (n = 48). Field stimulation of the sympathetic nerves innervating the vas deferens produced excitatory junction potentials (e.j.ps) which reached a mean magnitude of 8.5 +/- 0.8 mV (n = 23) when fully facilitated at a stimulation frequency of 0.5 Hz. 3. Introduction of suramin 1 - 100-mu-M produced no change in the resting membrane potential of the smooth muscle cells, but gradually reduced ej.p. magnitude. Suramin, 20-mu-M, reduced the mean magnitude of the fully facilitated e.j.ps to 1.4 +/- 0.3 mV (n = 18). 4. After suramin-induced inhibition of e.j.ps, nerve stimulation at 1- 8 Hz resulted in summation of e.j.ps to a subthreshold level. Subsequent introduction of the alpha-adrenoceptor antagonists, prazosin or phentolamine (1-mu-M) did not reduce the magnitude of the summated e.j.ps. 5. The results support the proposal that e.j.ps in vas deferens are mediated by adenosine 5'-triphosphate, and not by noradrenaline, and confirm that suramin can antagonize responses mediated via P2-purinoceptors.