Tanshinone II-A sodium sulfonate (DS-201) enhances human BK(Ca) channel activity by selectively targeting the pore-forming α subunit

AIM: Tanshinone II-A sodium sulfonate (DS-201), a water-soluble derivative of Tanshinone II-A, has been found to induce vascular relaxation and activate BK(Ca) channels. The aim of this study was to explore the mechanisms underlying the action of DS-201 on BK(Ca) channels. METHODS: Human BK(Ca) channels containing α subunit alone or α plus β1 subunits were expressed in HEK293 cells. BK(Ca) currents were recorded from the cells using patch-clamp technique. The expression and trafficking of BK(Ca) subunits in HEK293 cells or vascular smooth muscle cells (VSMCs) were detected by Western blotting, flow cytometry and confocal microscopy. RESULTS: DS-201 (40–160 μmol/L) concentration-dependently increased the total open probability of BK(Ca) channels in HEK293 cells, associated with enhancements of Ca(2+) and voltage dependence as well as a delay in deactivation. Coexpression of β1 subunit did not affect the action of DS-201: the values of EC(50) for BK(Ca) channels containing α subunit alone and α plus β1 subunit were 66.6±1.5 and 62.0±1.1 μmol/L, respectively. In both HEK293 cells and VSMCs, DS-201 (80 μmol/L) markedly increased the expression of α subunit without affecting β1 subunit. In HEK293 cells, DS-201 enriched the membranous level of α subunit, likely by accelerating the trafficking and suppressing the internalization of α subunit. In both HEK293 cells and VSMCs, DS-201 (≥320 μmol/L) induced significant cytotoxicity. CONCLUSION: DS-201 selectively targets the pore-forming α subunit of human BK(Ca) channels, thus enhancing the channel activities and increasing the subunit expression and trafficking, whereas the β1 subunit does not contribute to the action of DS-201.