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

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.

The role of calcium and alpha-adrenoceptors in contractile response of chick expansor secundariorum muscle to field stimulation.

1. The effects of some alpha-adrenergic agonists and antagonists on electrically-evoked contractions and tension of chick expansor secundariorum muscle (ESM), and dependence of these events on extracellular calcium was investigated. 2. Both train and continuous electrical stimulation can produce regular contractions in preparations obtained from 40-60 day old chicks. 3. Clonidine had a biphasic action on the contractions produced by train electrical stimulation. In concentrations ranging from 10(-8) to 3 x 10(-7) M, clonidine decreased the contraction amplitude, but in higher concentrations, it caused an increase in both the muscle tension and the contraction amplitude. These effects were reversed by application of yohimbine although yohimbine by itself had no effect on the contractions. 4. Introduction of calcium free isotonic high potassium medium decreased muscle tone which was followed by further dose-dependent increase in tension, along with the addition of cumulative doses of CaCl2 (ED50 = 2.8 x 10(-3) M). 5. Nifedipine reduced the amplitude of ESM contractions produced by continuous electrical stimulation in a dose dependent manner (IC50 = 6.7 x 10(-7) M). 6. Methoxamine induced a completely dose dependent increase in muscle tension which was dependent on extracellular calcium and was inhibited by nifedipine. In the presence of 10(-8) M nifedipine, ED50 of methoxamine stimulatory effect increased from the control value of 2.2 x 10(-7) to 8.4 x 10(-7) M).(ABSTRACT TRUNCATED AT 250 WORDS)