Effects of Panax notoginseng saponin Rb1 and Rg1 on myocardial action potential and slow inward current

The effects of Rb1, Rg1 (purified saponin of Panax notoginseng) on contraction force, action potential and slow inward current of guinea pig papillary muscles were studied by intracellular microelectrodes and voltage clamp techniques. The contraction force was decreased and the APD20 was shortened in the presence of Rb1 1 mg/ml, while the RP, APA and Vmax remained unchanged. The amplitude of Isi was decreased from a peak value of 9.8 +/- 1.6 to 7.3 +/- 3.4 microA after 20 min perfusion with Rb1 solution. This effect was reversed by increasing calcium concentration. Rg1 1 mg/ml decreased the contraction force significantly without affecting the configuration of action potential and the amplitude of slow inward current. The results indicate that Rb1 has a blocking effect on calcium channels, but Rg1 has not.