AIM: To observe the cellular electrophysiological effect of 3,6 dimethylamino dibenzopyriodonium of ferric EDTA(IHC 66,
1～50 μmol·L -1 ). METHODS: Using myocardium intracellular microelectrode techniques in isolated canine cardiac
Purkinje fibers and ventricular muscles. RESULTS: The initial effects of IHC 66 consisted of shortening of the duration of action potential measured at 20%(APD 20 ) and 50%(APD 50 ) of repolarization while the maximal depolarization rate of action potential of phase 0 (Vmax) was decreased in isolated ventricular muscles and APD 50 was shortened in isolated canine cardiac Purkinje fibers when the preparation was superfused with bath solution containing IHC 66 5 μmol·L -1 for 15 min. The inhibition effects of APD 20 and Vmax were also observed in Purkinje fibers with increasing drug concentration (10 and 30 μmol·L -1 ). At higher concentration (30 μmol·L -1 and above), IHC 66 decreased the amplitude of action potential and prolonged the duration of action potential measured at 90%(APD 90 ) of repolarization in isolated ventricular muscles of canine cardiac Purkinje fibers but without any significant effect on the resting potential. IHC 66 30 μmol·L -1 produced a frequency dependent depression of Vmax while altering stimulating frequency between 0 3～5 Hz in isolated Purkinje fibers. CONCLUSION: The inhibition effects of IHC 66 on
action potentials in isolated canine cardiac muscles were more powerful than that in isolated canine cardiac Purkinje fibers. IHC 66(30 μmol·L -1 ) produced a frequency dependent depression of Vmax.