Effects of S(+)-efonidipine on the rabbit sinus node action potential and calcium channel subunits CaV1.2, CaV1.3 and CaV3.1

The effect of S(+)-efonidipine on sinus node action potential and calcium channel α-subunits was examined. The slope of the phase 4 depolarization of isolated rabbit sinus node tissue was significantly reduced by S(+)-efonidipine (1 μM), slightly reduced by nifedipine (1 μM), but was not affected by R(−)-efonidipine. S(+)-efonidipine (1 μM), inhibited the expressed CaV1.2, CaV1.3 and CaV3.1 channel currents by 75.7%, 75.3% and 94.0%, nifedipine 84.0%, 43.2% and 14.9%, and R(−)-efonidipine 30.0%, 19.6% and 92.8%, respectively. Thus, the prolongation of the phase 4 depolarization of the rabbit sinus node by S(+)-efonidipine may be explained by blockade of the CaV1.3 channel current.