Activation of high conductance Ca2+-activated K+ channels by sodium tanshinoneII-A sulfonate (DS-201) in porcine coronary artery smooth muscle cells

High conductance Ca2+ activated K+ channels (BKCa) in vascular smooth muscles play important roles in controlling the vascular tone by determining the level of membrane potential and Ca2+ influx through voltage gated Ca2+ channels. Agents that alter the activity of Ca2+ channels or BKCa thus affect the vascular tone in both physiological and pathological conditions. Danshen, the dried root of Salvia miltiorrhiza, is a commonly used traditional Chinese medicine and is widely used as an effective remedy for cardiovascular and cerebral vascular diseases partly by its vasodilatation. Sodium tanshinoneII-A sulfonate (DS-201) is a water-soluble derivative of Tanshinone IIA, the main active component of Danshen. The purpose of this study was to explore possible mechanisms of vasodilative effects of DS-201 using porcine coronary artery smooth muscle. DS-201 induced relaxation of the coronary smooth muscle which had been contracted with 30 mM KCl, and the relaxation was inhibited by 100 nM iberiotoxin (IbTX), a specific BKCa channel blocker. Using perforated whole-cell recordings and single channel recordings, effects of DS-201 on BKCa were examined. The results showed that DS-201 activated BKCa. Extracellular application of DS-201 at 40, 80 µM under the whole-cell configuration induced increases of the BKCa macroscopic currents by 43.6%, 42.1% respectively, and the spontaneous transient outward K+ currents (STOCs) by 48.7%, 47.4% respectively. In inside-out patches, bath application of 20–150 μM of DS-201 activated BKCa by 5.4–173.2 fold. These results indicate that the vasodilatation by DS-201 is related to activation of BKCa.