DIFFERENTIAL-EFFECTS OF PINACIDIL, CROMAKALIM, AND NS-1619 ON ELECTRICALLY-EVOKED CONTRACTIONS IN RAT VAS-DEFERENS

AIM: To compare the inhibitory action of electrically evoked contracti ons of rat epididymal vas deferens by pinacidil (Pin), cromakalim (Cro ), and NS 1619. METHODS: Monophasic contractions were evoked by electr ic field stimulation in rat isolated epididymal half of vas deferens. RESULTS: Newly developed ATP-sensitive K+ channel openers, Pin and Cro , concentration-dependently reduced the electrically evoked (0.3 Hz, 1 ms pulse duration, 60 V) contractions and glibenclamide but not chary bdotoxin antagonized the inhibitory effects of both agents. Pin shifte d the concentration-response curve for norepinephrine to the right wit h reducing the magnitude of the maximum contraction in a glibenclamid- sensitive fashion. The large-conductance Ca2+-activated K+ channel ope ner, NS 1619, inhibited the electrically evoked contractions in a conc entration-dependent manner. Charybdotoxin (100 nmol.L-1) partially red uced the effect of NS 1619 but glibenclamide (10 mu mol.L-1) showed no effect. None of these 3 agents affected the basal tension. Both ATP-s ensitive and Ca2+-activated K+ channels presented in vas deferens smoo th muscles involved in regulation of muscle contractility.