Different calcium dependencies of contractile activity of prostatic and epididymal portions of rat vas deferens

Abstract

1. The effects of some organic calcium entry blockers and different concentrations of extracellular calcium on electrically-evoked contractions of isolated epididymal and prostatic portions of rat vas deferens were investigated. 2. Both epididymal and prostatic parts of rat vas deferens responded to single pulse or train electrical field stimulation, with twitch contractions of submaximal amplitude. 3. Verapamil showed a biphasic action on the contractions produced by single pulse electrical stimulation. In concentrations < 10(-5) M, it potentiated the responses of both portions, but at higher concentrations, the excitatory action was overcome by a concentration-dependent inhibitory effect. 4. Nifedipine reduced the amplitude of electrically-evoked contractions of both portions in a concentration-dependent manner. The ED50 of nifedipine was 3.6 x 10(-8) M and 2.1 x 10(-6) M in prostatic and epididymal portions, respectively. 5. Dantrolene sodium reduced the amplitude of electrically-evoked contractions of both portions in a concentration-dependent manner. The ED50 of dantrolene was 1.55 x 10(-4) M and 9.1 x 10(-4) M in prostatic and epididymal portions, respectively. 6. Reduction of Ca2+ concentration in medium reduced the amplitude of contractions of both portions significantly. This calcium dependence was more apparent in low frequencies of electrical stimulation.