Effect of timosaponin A-III, from Anemarrhenae asphodeloides Bunge (Liliaceae), on calcium mobilization in vascular endothelial and smooth muscle cells and on vascular tension

Abstract

The effects of timosaponin A-III (TA-III), from Rhizoma Anemarrhenae, on Ca 2+ mobilization in vascular endothelial cells and smooth muscle cells and on vascular tension have been explored. TA-III increased intracellular Ca 2+ concentrations ([Ca 2+] i) in endothelials cells at a concentration larger than 5 μM with an EC 50 of 15 μM, and increased [Ca 2+] i in smooth muscle cells at a concentration larger than 1 μM with an EC 50 of 8 μM. Within 5 min, the [Ca 2+] i signal was composed of a gradual rise, and the speed of rising depended on the concentration of TA-III. The [Ca 2+] i signal was abolished by removing extracellular Ca 2+ and was recovered after reintroduction of Ca 2+. The TA-III-induced [Ca 2+] i increases in smooth muscle cells were partly inhibited by 10 μM nifedipine or 50 μM La 3+, but was insensitive to 10 μM verapamil and diltiazem. TA-III (10–100 μM) inhibited 0.3 μM phenylephrine-induced vascular contraction, which was abolished by pretreatment with 100 μM N ω-nitro-L-arginine (L-NNA) or by denuding the aorta. TA-III also increased [Ca 2+] i in renal tubular cells with an EC 50 of 8 μM. Collectively, the results show for the first time that TA-III causes [Ca 2+] i increases in the vascular system. TA-III acted by causing Ca 2+ influx without releasing intracellular Ca 2+. TA-III induced relaxation of phenylephrine-induced vascular contraction via inducing release of nitric oxide from endothelial cells.