Effects of neferine on transmembrane potentials of guinea pig myocardium
Neferine, an alkaloid first isolated from the seed embryo of Nelumbo nucifera Gaertn in China, possesses an anti-arrhythmic action. The effects on the action potential duration (APD) and the maximal upstroke velocity (Vmax) in different driving rates, the slow response action potentials of K+-depolarized ventricular myocardium and the ouabain-induced oscillatory potentials were studied in guinea pig papillary muscles. Neferine 10 and 50 mumols/L markedly suppressed the transmembrane potentials Vmax at 0.1-5 Hz. It (50 mumols/L) prolonged the APD at 0.5-5 Hz. Neferine 10-100 mumols/L inhibited the contractility, amplitude of action potentials and Vmax of K+-depolarized guinea pig papillary muscles in a concentration-dependent manner, and 100 mumols/L decreased the amplitude of action potentials and Vmax from 73 +/- 7 mV and 6.0 +/- 1.7 V/s of control to 57 +/- 4 mV and 3.2 +/- 0.7 V/s, respectively. In addition, neferine 50 mumols/L abolished the oscillatory potentials induced by ouabain. The results indicate that the effects of neferine on APD and Vmax seem not to be related to the frequency of stimuli, and its anti-arrhythmic action is relevant to the inhibitory effects on Na+, K+, Ca2+ currents of myocardium.