Inhibition of Large-Conductance Calcium-Activated Potassium Channel by 2-Methoxyestradiol in Cultured Vascular Endothelial (HUV-EC-C) Cells

Abstract.

2-Methoxyestradiol, an endogenous metabolite of 17β-estradiol, is known to have antitumor and antiangiogenic actions. The effects of 2-methoxyestradiol on ionic currents were investigated in an endothelial cell line (HUV-EC-C) originally derived from human umbilical vein. In the whole-cell patch-clamp configuration, 2-methoxyestradiol (0.3–30 μm) reversibly suppressed the amplitude of K⁺ outward currents. The IC ₅₀ value of the 2-methoxyestradiol-induced decrease in outward current was 3 μm. Evans blue (30 μm) or niflumic acid (30 μm), but not diazoxide (30 μm), reversed the 2-methoxyestradiol-induced decrease in outward current. In the inside-out configuration, application of 2-methoxyestradiol (3 μm) to the bath did not modify the single-channel conductance of large-conductance Ca²⁺-activated K⁺ (BK_Ca) channels; however, it did suppress the channel activity. 2-Methoxyestradiol (3 μm) produced a shift in the activation curve of BK_Ca channels to more positive potentials. Kinetic studies showed that the 2-methoxyestradiol-induced inhibition of BK_Ca channels is primarily mediated by a decrease in the number of long-lived openings. 2-Methoxyestradiol-induced inhibition of the channel activity was potentiated by membrane stretch. In contrast, neither 17β-estradiol (10 μm) nor estriol (10 μm) affected BK_Ca channel activity, whereas 2-hydroxyestradiol (10 μm) slightly suppressed it. Under current-clamp condition, 2-methoxyestradiol (10 μm) caused membrane depolarization and Evans blue (30 μm) reversed 2-methoxyestradiol-induced depolarization. The present study provides evidence that 2-methoxyestradiol can suppress the activity of BK_Ca channels in endothelial cells. These effects of 2-methoxyestradiol on ionic currents may contribute to its effects on functional activity of endothelial cells.