Effects of tetrandrine on action potential and contraction of isolated guinea pig papillary muscles

The pffects of tetrandrine on action poteritial and contraction were studied in isolated guinea pig papillary muscles in normal and K+ -- rich Tyrodeis solution. Tetrandririe produced conccntration-dependent negative inotropic effpcts and shortened APD20 and APD90. But resting potential and amplitude of action potential were not influenced. Thus. an excitation-contraction uncoupling was seen. Tetranarine decreased the amplitude of Ca++ - mediated slow action potential induced by high K+. These results are in contrast with those of quinidine and indicate that tetrandrine can be considered as a blocker of the slow channel.