Changes of action potential and L-type calcium channel current of Sprague-Dawley rat ventricular myocytes by different amlodipine isomers

To investigate the effects of S- and R-amlodipine (Aml) on action potential (AP) and L-type calcluim channel Current (ICa-L), the whole-cell patch-clamp technique was used on rat ventricular mocytes to record AP, I-Ca-L,I- peak currents, steady-state activation currents, steady-state inactivation cut-rents, and recovery currents from inactivation with S-Aml and R-Aml at various concentrations. Increasing concentrations of S-Aml gradually shortened AP durations (APDs). At concentrations of 0.1, 0.5, 1, 5, and 10 mu mol/L, S-Aml blocked 1.5% +/- 0.2%, 25.4% +/- 5.3%. 65.2% +/- 7.3%, 78.4% +/- 8.1%, and 94.2% +/- 5.0% of ICa-L, respectively (p < 0.05), and the half-inhibited concentration was 0.62 +/- 0.12 mu mol/L. Current-voltage curves were shifted upward; steady-state activation and inactivation curves were shifted to the left. At these concentrations of S-Aml, the half-activation voltages were -16.01 +/- 1.65.1 -17.61 +/- 1.60, -20.17 +/- 1.46, -21.87 +/- 1.69, and -24.09 +/- 1.87 mV, respectively, and the slope factors were increased (1) < 0.05). The half-inactivation voltages were -27.16 +/- 4.48, -28.69 +/- 4.52, -31.19 +/- 4.17, -32.63 +/- 4.34, and -35.16 +/- 4.46 mV., respectively, and the slope factors were increased (p < 0.05). The recovery times from inactivation of S-Aml were prolonged (p < 0.05). In contrast, R-Aml had no effect on AP and ICa-L (p > 0.05) at the concentrations tested. Thus, only S-Aml has calcium channel blockade activity, whereas R-Aml has none of the phamacologic actions associated with calcium channel blockers.