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

The effects of timosaponin A-III (TA-III), from Rhizoma Anemarrhenae, on Ca²⁺ mobilization in vascular endothelial cells and smooth muscle cells and on vascular tension have been explored. TA-III increased intracellular Ca²⁺ concentrations ([Ca²⁺]_i) in endothelials cells at a concentration larger than 5 μM with an EC₅₀ of 15 μM, and increased [Ca²⁺]_i in smooth muscle cells at a concentration larger than 1 μM with an EC₅₀ of 8 μM. Within 5 min, the [Ca²⁺]_i signal was composed of a gradual rise, and the speed of rising depended on the concentration of TA-III. The [Ca²⁺]_i signal was abolished by removing extracellular Ca²⁺ and was recovered after reintroduction of Ca²⁺. The TA-III-induced [Ca²⁺]_i increases in smooth muscle cells were partly inhibited by 10 μM nifedipine or 50 μM La³⁺, 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 [Ca²⁺]_i in renal tubular cells with an EC₅₀ of 8 μM. Collectively, the results show for the first time that TA-III causes [Ca²⁺]_i increases in the vascular system. TA-III acted by causing Ca²⁺ influx without releasing intracellular Ca²⁺. TA-III induced relaxation of phenylephrine-induced vascular contraction via inducing release of nitric oxide from endothelial cells.