Differential effects of pinacidil, cromakalim, and NS 1619 on electrically evoked contractions in rat vas deferens
Abstract
AIM: To compare the inhibitory action of electrically evoked contractions of rat
epididymal vas deferens by pinacidil (Pin), cromakalim (Cro), and NS 1619.
METHODS: Monophasic contractions were evoked by electric 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 charybdotoxin antagonized
the inhibitory effects of both agents. Pin shifted the concentration-response
curve for norepinephrine to the right with reducing the magnitude of the maximum
contraction in a glibenclamide-sensitive fashion. The large-conductance
Ca(2+)-activated K+ channel opener, NS 1619, inhibited the electrically evoked
contractions in a concentration-dependent manner. Charybdotoxin (100 nmol.L-1)
partially reduced the effect of NS 1619 but glibenclamide (10 mumol.L-1) showed
no effect. None of these 3 agents affected the basal tension.
CONCLUSION: Both ATP-sensitive and Ca(2+)-activated K+ channels presented in vas
deferens smooth muscles involved in regulation of muscle contractility.
Keywords:
epididymal vas deferens by pinacidil (Pin), cromakalim (Cro), and NS 1619.
METHODS: Monophasic contractions were evoked by electric 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 charybdotoxin antagonized
the inhibitory effects of both agents. Pin shifted the concentration-response
curve for norepinephrine to the right with reducing the magnitude of the maximum
contraction in a glibenclamide-sensitive fashion. The large-conductance
Ca(2+)-activated K+ channel opener, NS 1619, inhibited the electrically evoked
contractions in a concentration-dependent manner. Charybdotoxin (100 nmol.L-1)
partially reduced the effect of NS 1619 but glibenclamide (10 mumol.L-1) showed
no effect. None of these 3 agents affected the basal tension.
CONCLUSION: Both ATP-sensitive and Ca(2+)-activated K+ channels presented in vas
deferens smooth muscles involved in regulation of muscle contractility.