EFFECTS OF SINOMENINE ON ACTION POTENTIAL AND FORCE OF CONTRACTION IN GUINEA PIG HEART MUSCLE

The effects of sinomenine (SIN) on action potential and force of contraction were investigated with glass microelectrode in guinea pig heart muscle. SIN at concentrations above 2.7 μmol/l exhibited a dose-dependent negative inotropic action and prolongation in the 20% and 90% repolarization (APD₂₀ and APD₉₀ and effective refractory period (ERP). SIN (27 μmol/l) decreased the maximal upstroke velocity (max) by 10±6%. The amplitude of action potential was also decreased. In the ventricular muscle pretreated with tetrodotoxin (TTX), SIN (27 μmol/l) decreased the amplitude of action potential and maximal rate of depolarization (MRD), and caused a marked prolongation of its duration. Moreover, the effect of acetylcholine (Ach 30 μmol/l) in shortening the APD of atrium was antagonized by SIN (82 μmol/l). These results indicate that SIN may unspecifically inhibit the current of Na⁺, Ca²⁺ and K⁺.