Blocking effect of rhynchophylline on calcium channels in isolated rat ventricular myocytes

The effect of rhynchophylline (Rhy) on L-type Ca2+ channel current was studied in rat ventricular myocytes using patch-clamp whole-cell recording technique. When the holding potential was -40 mV, cells were depolarized to 0 mV for 250 ms at frequency of 0.5 Hz, Rhy 10 and 50 mumol.L-1 reduced verapamil-sensitive Ca2+ inward current by 60% and 80%, respectively, without affecting the voltage-dependency of the maximal activation of Ca2+ current. This indicated that the effect of Rhy on the activation of Ca2+ channel was voltage-independent. The effect of Rhy on Ca2+ current reached the maximum at 10 min and was partially recovered by washout of Rhy. A pD2 value of 5.91 and Hill coefficient of 1.1 were obtained from the concentration-response curve.