AN ELECTROPHYSIOLOGICAL INVESTIGATION OF THE ACTIONS OF SOME AUTONOMIC BLOCKING DRUGS ON TRANSMISSION IN THE GUINEA-PIG VAS DEFERENS.

Membrane potentials have been recorded from the guinea-pig isolated vas deferens with intracellular and sucrose-gap electrodes during stimulation of the hypogastric nerve and of intramural nerve fibres. Atropine had no detectable effect on the excitatory junction potentials in response to nerve stimulation or on the spontaneous discharge of small potentials. High concentrations of adrenolytic drugs, acting on alpha-receptors were needed to block the response to nerve stimulation and the spontaneous discharge. During the onset and recovery from yohimbine blockade, junction potentials in response to repetitive stimulation were not sustained. Bretylium initially reduced both the junction potentials and the spontaneous discharge. However, after 30 min exposure, the spontaneous discharge increased in frequency although the response to nerve stimulation was abolished. Block of the junction potentials by procaine was rapid in onset compared with that by bretylium and guanethidine, but the spontaneous discharge was not abolished. These results are discussed in relation to the mechanism of transmission from sympathetic nerve to smooth muscle.