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, vera pamil, papaverine and chloroethylclonidine (CEC) on the electrically-induce d contractions and on the contractions produced by exogenous noradrenaline and alpha,beta 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 th e contractile response to single-pulse field stimulation but inhibited the response to alpha,beta methylene-ATP. Papaverine left unaffected phase I bu t depressed the response to alpha,beta methylene-ATP. CEC significantly pot entiated,the purinergic component of the electrically-evoked response and t he response induced by alpha,beta methylene-ATP. 3 Nifedipine was devoid of any inhibitory action on the noradrenergic compo nent (phase II) of the response to single shock. Verapamil at the highest c oncentration used (10(-5) M) was able to partially inhibit phase II. Papave rine abolished in a concentration-dependent manner the noradrenergic compon ent of the response to single shock. CEC abolished the phase II of single s hock 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.