Effects of furyl-dihydropyridine on action potential ventricular myocardium of rabbit in vivo and isolated guinea pig left atrium in vitro

Effects of furyl-dihydropyridine (FDP) on action potential of rabbit ventricular myocardium in vivo were observed with floating microelectrode technique. FDP 0.5 mg.kg-1 i.v. increased APD30 from 104 +/- 7 to 127 +/- 7 ms, APD90 from 146 +/- 10 to 177 +/- 9 ms (P < 0.01, n = 7), decreased the heart rate from 230 +/- 18 to 203 +/- 20 bpm (P < 0.05). Nifedipine (Nif) 0.5 mg.kg-1 i.v. reduced APD and increased the HR in rabbit. In guinea pig left atrium, FDP and Nif decreased the APD, the effects of acetylcholine to shorten the APD was antagonized by FDP 1 mumol.L-1. In rabbit's sinoatrial nodes, FDP 0.5, 1 mumol.L-1 also suppressed the APA and increased the spontaneous sinus cycle length (SCL) and APD50. These results indicate that FDP may inhibit the Ca2+ and K+ currents of myocardium.