Effects of neferine on transmembrane potential in rabbit sinoatrial nodes and clusters of cultured myocardial cells from neonatal rats

Neferine (Nef), a bis-benzylisoquinoline alkaloid first isolated from the seed embryo of Nelumbo nucifera G in China, possesses an anti-arrhythmic action. The effects of Nef on the transmembrane potential were studied in rabbit sinoatrial nodes and the clusters of cultured cardiac myocytes from neonatal rats. Nef 30 mumol/L suppressed the amplitude of action potential (APA) from 57 +/- 5 to 42 +/- 4 mV, and the maximal upstroke velocity (Vmax) from 1.7 +/- 0.3 to 0.9 +/- 0.4 V/s (n = 5, P less than 0.0) in rabbit sinoatrial nodes. Nef (40 mumol/L) decreased the APA from 92 +/- 8 mV of control to 80 +/- 4 mV, and Vmax from 20 +/- 5 to 12 +/- 4 V/s (P less than 0.01) in the clusters of cultured cardiac myocytes from neonatal rats. The effects on APA and Vmax were concentration-dependent. The results indicate that Nef has an inhibitory effect on the slow transmembrane Na+ and/or Ca2+ current of myocardium.