Spontaneous contractions and membrane activity of castrated guinea-pig vas deferens

Castration of the guinea pig was followed by atrophy of the vas deferens and appearance of spontaneous contractions. Testosterone replacement reversed those effects and diethylstilbestrol treatment increased them. A month after castration or castration and stilbestrol treatment (15 mg/30 days), the membrane exhibited depolarization and spontaneous spikes that were not seen with the normal groups. The spontaneous contractions observed with both groups reflected the occurrence of membrane spikes. Tetrodotoxin (3 c 10(-6) M) did not change the membrane potential in any organ studied nor did it affect the pattern of spontaneous contractions. Verapamil (5 x 10(-6) M) increased the membrane potential of the muscles from castrated and stilbestrol-treated castrated animals, abolished the membrane spikes and blocked the spontaneous contractions. The results suggest that castration increases calcium permeability through the membrane. The increase in calcium permeability would be responsible for muscle rhythmicity.