Abstract: The effects of tetrandrine (Tet) on cytosolic free calcium ([Ca²⁺]i) in subcultured bovine aortic smooth muscle cells (SMC) were studied by Fura-2 and AR-CM-MIC cation measurement system. Tet (1~100 μmol·L^-1) had no effect on the resting [Ca²⁺]i, but had inhibitory effects on [Ca²⁺]i elevation induced by high K⁺, 5-HT, ATP, Ang II and NE in the presence of extracellular Ca²⁺. High concentration of Tet also inhibited Phe-induced [Ca²⁺]i elevation in absence of extracellular Ca²⁺. Tet (1~100 μmol·L^-1) inhibited KCl (60 mmol·L^-1) induced [Ca²⁺]i elevation in dose-dependent manner, the IC50 value was 9.2 (95% confidence limits: 5.7~14.9) mmol·L^-1. The results suggested that Tet had blocking effects on both VOC and ROC in bovine aortic SMC. It appears that the mechanisms of blocking effect of Tet on ROC might be primarily due to its Ca²⁺ entry blocking effects.

Key words: Tetrandrine, Vascular smooth muscle cell, Fura-2, Calcium channel blockers