An electrophysiological study of the effects of atropine and physostigmine on transmission to the guinea-pig vas deferens

Abstract

1. The effects of physostigmine and atropine on transmission to the longitudinal musculature of in vitro preparations of the guinea-pig vas deferens have been examined using intracellular micro-electrodes.2. Atropine (5 x 10(-7) to 10(-6) g/ml.) increased the rate of decay of excitatory junction potentials (EJPs) in response to post-ganglionic stimulation.3. Physostigmine (5 x 10(-6) g/ml.) reduced the mean resting potential of the muscle cells from -60.5 to -51.5 mV and lowered the voltage of post-ganglionic stimulation necessary for initiation of an action potential in the muscle. In some but not all of the cells studied the time course of the EJP was markedly prolonged.4. At concentrations which did not alter the response to post-ganglionic stimulation (5 x 10(-7) to 10(-6) g/ml.), physostigmine caused fully facilitated EJPs to appear with the first pulse of a preganglionic train of stimulation.5. Atropine antagonized all the above effects of physostigmine.6. Physostigmine (5 x 10(-7) to 10(-6) g/ml.) also lowered the voltage of preganglionic stimulation necessary for initiation of an action potential in the muscle. This effect was not antagonized by atropine.7. The results are interpreted as being evidence for the existence of separate cholinergic and adrenergic motor fibres to the musculature of the guinea-pig vas deferens.