Effects of quinine and quinidine on the transient outward and on the L-type Ca2+ current in rat ventricular cardiomyocytes

The effects of the enantiomers quinine and quinidine on the transient outward current (I-to) and on the L-type Ca2+ current (I-Ca) were investigated in rat ventricular cardiomyocytes using the patch-clamp technique. At a stimulation frequency of 2 Hz, both quinine depressed the magnitude of I-to and I-Ca; the half-maximal effects on Ito were achieved at 11 and 15 mumol/l, respectively, and those on I-Ca at 14 and 10 mumol/l, respectively. At 0.2 Hz, both drugs depressed the magnitude of I-to, but not that of I-Ca. A change in extracellular pH from 7.3 to 8.3 did not significantly influence the effects of the drugs (which are protonated to 98% at pH 7.3) on I-to or I-Ca. It is concluded that neither the different chemical structure nor the amount of protonation of quinine and quinidine controls their effects on I-to or I-Ca. Copyright (C) 2002 S. Karger AG, Basel.