EFFECTS OF TETRANDRINE ON CYTOSOLIC-FREE CALCIUM IN CULTURED RAT MYOCARDIAL-CELLS

AIM: To study the effects of tetrandrine (Tet) on myocardium. METHODS: Using Fura 2-AM and AR-CM-MIC cation measurement system, cytosolic fr ee calcium ([Ca2+](i)) was examined in cultured rat single myocardial cells. RESULTS: The resting [Ca2+](i) was 90 +/- 12 nmol . L(-1) in th e presence of Ca2+ 1.3 mu mol . L(-1) in Hanks' solution. Tet 1 - 100 mu mol . L(-1) had no effect on the resting [Ca2+](i), but 10 - 100 mu mol . L(-1) depressed the [Ca2+](i) elevation when extracellular Ca2 was 5 mmol . L(-1). Tet 1 - 100 mu mol . L(-1) inhibited KCl (30 and 60 mmol . L(-1)) induced [Ca2+](i) elevation in a concentration-depend ent manner, the IC50 value was 8.8 mu mol . L(-1) (95 % confidence lim its: 3.3 - 23.7 mu mol . L(-1)) and 6.9 mu mol . L(-1) (95 % confidenc e limits: 2.8 - 17.4 mu mol . L(-1)), respectvely. Norepinephrine (NE) 10 mu mol L(-1) caused a rapid increase in [Ca2+](i) in the presence or abscence of extracellular Ca2+, Tet 30 - 100 mu mol . L(-1) only de creased the former. Tet 10 - 100 mu mol . L(-1) also decreased ouabain (Oua)-induced elevation in [Ca2+](i). CONCLUSION: Tet had inhibitory effects on Ca2+ transmembrane movement, but it is not a selective calc ium channel blocker in rat myocardial cells.