DIFFERENTIAL BLOCKADE OF ALPHA , BETA -METHYLENE-ATP, NORADRENALINE AND ELECTRICALLY EVOKED CONTRACTIONS OF THE RAT VAS DEFERENS

1 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 α,β methylene-ATP in the epidydimal portion of rat vas deferens. 2 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 α,β methylene-ATP. Papaverine left unaffected phase I but depressed the response to α,β methylene-ATP. CEC significantly potentiated the purinergic component of the electrically-evoked response and the response induced by α,β methylene-ATP. 3 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. 4 The implications of these differences among the compounds studied in the present work are discussed in relation to roles of calcium channels.