EFFECTS OF POTASSIUM CHANNEL OPENERS AND CALCIUM-CHANNEL BLOCKERS ON THE FORCE RESPONSES OF THE ELECTRICALLY DRIVEN RAT RIGHT VENTRICLE STRIP

1 The effects of potassium channel openers (cromakalim and pinacidil) and of calcium channel blockers (verapamil, diltiazem and flunarizine) on the contractile responses of the rat right ventricle have been determined. 2 On the electrically driven rat right ventricle cromakalim at 3 X 10(-7), 10(-6), 3 X 10(-6) M and 10(-5) M, and pinacidil at 10(-6), 10(-5) and 3 X 10(-5) M had no effect on the force responses to cardiac stimulation or to isoprenaline. 3 Pinacidil at 10(-4) M in a vehicle of 0.7% ethanol reduced the force responses to cardiac stimulation. This inhibitory effect was solely due to the ethanol. Pinacidil in 5 X 10(-4) M HCl (which had no effect alone) potentiated some of the responses to isoprenaline. 4 Verapamil greater-than-or-equal-to 10(-6) M, diltiazem, greater-than-or-equal-to 10(-5) M, and flunarizine, greater-than-or-equal-to 10(-6) M, reduced the force responses to cardiac stimulation and to isoprenaline. 5 The present study has shown that calcium channel blockers, but not potassium channel openers, have inhibitory effects on the rat right ventricle.