Salvianolic acid B, an aqueous component of danshen (Salvia miltiorrhiza), relaxes rat coronary artery by inhibition of calcium channels

In this study, we have investigated the mechanism of action through which salvianolic acid, a constituent of the medicinal herb danshen (Salvia miltiorrhiza), causes relaxation of isolated coronary artery rings precontracted with 1 μM 5-hydroxytryptamine (5-HT). The vasorelaxant effects of salvianolic acid B were also compared with the aqueous extract of danshen. Extraction of the water-soluble fraction from danshen provided a yield of 17.5%. The amount of salvianolic acid B determined in this aqueous extract was 3.9%, and the extract was 6.3 times less potent than salvianolic acid B in relaxing 5-HT-precontracted coronary artery rings; IC50 values were 930.3 ± 133.5 μg/ml and 147.9 ± 17.4 μg/ml, respectively. Removal of the endothelium did not significantly affect their vasodilator potencies; IC50 values were 842.1 ± 123.8 μg/ml and 160.3 ± 25.9 μg/ml. On the other hand, a potassium channel inhibitor tetraethylammonium (TEA, 10 mM) shifted their concentration-response curves by 1.7 and 2.9 folds. The possible involvement of Ca2+ channels was investigated in artery rings incubated with Ca2+-free buffer and primed with 1 μM 5-HT or 60 mM KCl for 5 min prior to adding CaCl2 to elicit contraction. In 5-HT-primed preparations, 2 mg/ml danshen aqueous extract and 0.72 mg/ml salvianolic acid B abolished the CaCl2-induced vasoconstriction, whereas, in KCl-primed preparations, 10 mg/ml danshen aqueous extract and 1.44 mg/ml salvianolic acid B produced 90% inhibition. These findings suggest the vasorelaxant effects of danshen aqueous extract and salvianolic acid B were produced by inhibition of Ca2+ influx in the vascular smooth muscle cells. The opening of K+ channels had a minor contribution to their effects, but endothelium-dependent mechanisms were not involved. The high vasodilator potency and the quantity of salvianolic acid B contained in danshen aqueous extract suggest it is an important vasodilator constituent in this medicinal herb.