Comparison of the electrophysiological effects of 4-aminoquinoline, quinidine and lidocaine on frog atrial contractile fibres.

Standard microelectrode techniques were used to study the electrophysiological effects of 4-aminoquinoline (4-AQ), a 4-aminopyridine analogue, on frog atrial contractile fibres and the effects compared with those of quinidine and lidocaine. The effects of 4-AQ (250 and 500 microM) were: reduction of action potential amplitude, overshoot and maximum upstroke velocity (Vmax) and increase of action potential duration. These effects were reversible after washing. No change in membrane resting potential was observed with these drug concentrations. Quinidine (27 and 54 microM) caused no statistically significant changes of resting potential and overshoot but dose-dependently decreased Vmax. Action potential duration (APD) was shortened or unchanged at 60% repolarization, whereas at 90% repolarization APD was increased by the higher concentration of this drug. Quinidine (54 microM) also depressed action potential amplitude. Lidocaine (17 microM) induced a slight decrease of action potential amplitude and a marked reduction of Vmax as well as of APD without changing membrane resting potential or overshoot. Comparison of these results indicate that 4-AQ and quinidine share most electrophysiological effects such as depression of upstroke velocity, action potential total amplitude and repolarization rate at phase 3 of the transmembrane potential. Lidocaine and 4-AQ share only the capability of decreasing Vmax, whereas the effect upon repolarization was the opposite. Consequently, this study together with a previous one of our laboratory (Guerrero, 1982) suggest that 4-AQ is a drug having some quinidine-like properties.