Differential blockade of alpha,beta-methylene-ATP, noradrenaline and electrically evoked contractions of the rat vas deferens.

The present study was carried out compare the effects of nifedipine, verapamil, papaverine and chloroethylclonidine (CEC) on the electrically-induced contractions and on the contractions produced by exogenous noradrenaline and alpha, beta methylene-ATP in the epidydimal portion of rat vas deferens. Nifedipine inhibited in a concentration-dependent fashion the purinergic component (phase I) of the electrically evoked response. Verapamil (10(-7) M-10(-5) M) did not inhibit significantly or even potentiated phase I of the contractile response to single-pulse field stimulation but inhibited the response to alpha,beta methylene-ATP. Papaverine left unaffected phase I but depressed the response to alpha,beta methylene-ATP. CEC significantly potentiated the purinergic component of the electrically-evoked response and the response induced by alpha,beta methylene-ATP. Nifedipine was devoid of any inhibitory action on the noradrenergic component (phase II) of the response to single shock. Verapamil at the highest concentration used (10(-5) M) was able to partially inhibit phase II. Papaverine abolished in a concentration-dependent manner the noradrenergic component of the response to single shock. CEC abolished the phase II of single shock while was devoid of any inhibitory action on exogenous noradrenaline. The implications of these differences among the compounds studied in the present work are discussed in relation to roles of calcium channels.