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 muM with an EC50 of 15 muM, and increased [Ca2+](i) in smooth muscle cells at a concentration larger than 1 muM with an EC50 of 8 muM. 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 muM nifedipine or 50 muM La3+, but was insensitive to 10 muM verapamil and diltiazem. TA-III (10-100 muM) inhibited 0.3 muM phenylephrine-induced vascular contraction, which was abolished by pretreatment with 100 muM N-omega-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 muM. Collectively, the results show for the first time that TA-III causes [Ca2+](i) increases in the vascular system. TA-Ill 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. (C) 2002 Elsevier Science Inc. All rights reserved.