Studies on the calcium antagonistic action of tetrandrine: X VI. Effects of tetrandrine on positive staircase phenomenon and post-rest potentiation of contraction of isolated guinea pig left atrium

Summary Tetrandrine (Tet) 0.32 mmol/1 and verapamil (Ver) 30 μmol/1 inversed positive staircase phenomenon of contraction in left alrium of guinea pig. After the preparation was partially depolarized with K₊ 20 mmol/1, such effect of Tet and Ver became much more pronounced. Propranolol could not inverse the positive staircase phenomenon. In addition, after treatment with Tet 0.32 mmol/1 for 20 min the post -rest potentiation of myocardial contraction in the left atrium was depressed by 2.8±0.3 g (P<0.01). The results suggest that the negative inotropism of Tet is related not only to the inhibition of Ca⁺⁺ influx to the cells, but also to the decrease of the intracellular Ca⁺⁺ release.