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 free calcium ([Ca2+]i) was examined in cultured rat single myocardial cells.

RESULTS

The resting [Ca2+]i was 90 +/- 12 nmol.L-1 in the presence of Ca2+ 1.3 mmol.L-1 in Hanks' solution. Tet 1-100 mumol.L-1 had no effect on the resting [Ca2+]i, but 10-100 mumol.L-1 depressed the [Ca2+]i elevation when extracellular Ca2+ was 5 mmol.L-1. Tet 1-100 mumol.L-1 inhibited KC1 (30 and 60 mmol.L-1) induced [Ca2+]i elevation in a concentration-dependent manner, the IC50 value was 8.8 mumol.L-1 (95% confidence limits: 3.3-23.7 mumol.L-1) and 6.9 mumol.L-1 (95% confidence limits: 2.8-17.4 mumol.L-1), respectively. Norepinephrine (NE) 10 mumol.L-1 caused a rapid increase in [Ca2+]i in the presence or absence of extracellular Ca2+, Tet 30-100 mumol.L-1 only decreased the former. Tet 10-100 mumol.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 calcium channel blocker in rat myocardial cells.