Electropharmacological actions of the constituents of Sinomeni Caulis et Rhizome and Mokuboi-to in guinea pig heart.

Cardiac actions of the constituents of Sinomeni Caulis et Rhizome (SCR) and Mokuboi-to, a traditional herbal drug, were investigated. In voltage-clamp experiments, sinomenine (1 mM) and tetrandrine (100 microM) inhibited the ionic currents concentration-dependently. The constituents affected the action potential configurations. In multicellular preparations, SCR (1 mg/ml) decreased the maximum rate of depolarization. Tetrandrine (30 microM) and sinomenine (300 microM) also had similar effects, but magnoflorine (1 mM) had less or no effect. Dysrhythmias were abolished under Ca(2+) overload conditions by sinomenine. These results indicate that at even acute administrations, these drugs exert the active electropharmacological actions and cardioprotections.