ELECTRICAL AND MECHANICAL RESPONSES OF THE BOVINE RETRACTOR PENIS TO NERVE STIMULATION AND TO DRUGS

Abstract

The response of the bovine retractor penis [BRP] muscle to field stimulation of intramural nerves in vitro was investigated using micro-electrode extracellular (sucrose gap) techniques. In the absence of tone single pulses or trains of stimuli (1-50 Hz 0.1-0.5 ms) produced ejp [intracellularly recorded excitatory responses to field stimulation] and a decrease in membrane resistance; spike potentials were not observed. EJp often small in amplitude (3-5 mV to single pulse) and accompanied by contractions in almost all preparations were noradrenergic, abolished by guanethidine (1-3 .times. 10-5 M) and tetrodotoxin (3.5 .times. 10-6 M) but not by prazosin (0.05-1.4 .times. 10-6 M). Prazosin abolished the depolarization and contraction produced by added NA [norepinephrine] (0.02-2 .times. 10-8 mol). TEA [tetraethylammonium] (10-2 M) depolarized the membrane and initiated spontaneous activity; EJp and contractions were enhanced and prolonged but no spikes were observed. Atropine (0.5 .times. 10-6 M) increased and physostigimine (1-5 .times. 10-6 M) decreased eip and contractions indicating a cholinergic regulatory component in the release of the excitatory transmitter. In the presence of tone, nerve stimulation produced iJp [intracellularly recorded inhibitory responses to field stimulation] and relaxations which were unaffected by apamin (5 .times. 10-7 M), atropine (3 .times. 10-6 M), guanethidine (3 .times. 10-5 M), phentolamine (5 .times. 10-6 M) and propranolol (4 .times. 10-6 M) but were abolished by tetrodotoxin (3.5 .times. 10-7 M) suggesting their mediation by non-adrenergic non-cholinergic (NANC) nerves. Sodium nitroprusside (10-10-10-8 mol), which increases cyclic GMP, also hyperpolarized the membrane and relaxed the BRP. Those responses and those to inhibitory nerve stimulation were antagonized by oxyhemoglobin which inhibits guanylate cyclase. 2-O-propoxyphenyl-8-azapurin-6-one (M and B 22948 3-9 .times. 10-6 M) which inhibits cGMP-specific phosphodiesterase, enhanced the relaxation but not the iJp. TEA (10-2 M) initially depolarized the membrane potential and raised tone. In the sucrose gap inhibitory potentials were abolished; the mechanical relaxation was not and a small contractile component emerged. Electrical and mechanical inhibitory components in the bovine retractor penis may not be correlated.