Effects of tetrandrine on positive staircase phenomena and post-rest potentiation of contraction of isolated guinea pig left atrium

Tetrandrine (Tet) 0.32 mmol/ L and verapamil (Ver) 30 μmol/L inversed positive staircase phenomena of contraction in left atrium of guinea pig. After the preparation was partially depolarized with K+ 20 mmol/L, such effect of Tet and Ver became much greater. Propranolol could not inverse the positive staircase phenomena. In addition, after the treatment of Tet 0.32 mmol/L for 20 min the post-rest potentiation of myocardial contraction in the left atrium was depressed by 2.8±0.3g (p<0.01). The results suggest that the negative inotropism of Tet are related not only to the inhibition of Ca2+ influx to the cells, but also to the decrease of the intracellular Ca2+ release.