Negative chronotropic and inotropic effects of Panax notoginseng saponins

The automatic beating rate of guinea pig isolated right heart atrium was slowed down and the positive chronotropic effect of CaC12 or isoprenaline was attenuated by Ponox notoginseng saponins (PNS) 1-3 mg/ml. The force of contraction of isolated left atrium and the positive inotropic effect of CaCl2 or isoprenaline were inhibited by PNS l-6 mg/ml. The inhibitory effects were dose- and frequency-dependent. Verapamil showed a similar effects to PNS. The electrophysiological study of transmem-brane potential of isolated right papillary muscle cells revealed that both the plateau phase and duration of the action potentials were shortened by PNS l mg/ml. The results indicate that PNS is probably a calcium antagonist similar to verapamil.