Inhibition of large-conductance calcium-activated potassium channel by 2-methoxyestradiol in cultured vascular endothelial (HUV-EC-C) cells

2-Methoxyestradiol, an endogenous metabolite of 17 beta -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 muM) reversibly suppressed the amplitude of K+ outward currents. The IC50 value of the 2-methoxyestradiol-induced decrease in outward current was 3 muM. Evans blue (30 muM) or niflumic acid (30 muM), but not diazoxide (30 muM), reversed the 2-methoxyestradiol-induced decrease in outward current. In the inside-out configuration, application of 2-methoxyestradiol (3 muM) to the bath did not modify the single-channel conductance of large-conductance Ca2+ activated K+ (BKCa) channels; however, it did suppress the channel activity. 2-Methoxyestradiol (3 muM) produced a shift in the activation curve of BKCa channels to more positive potentials. Kinetic studies showed that the 2-methoxyestradiol-induced inhibition of BKCa 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 17 beta -estradiol (10 muM) nor estriol (10 muM) affected BKCa channel activity, whereas 2-hydroxyestradiol (10 muM) slightly suppressed it. Under current-clamp condition, 2-methoxyestradiol (10 muM) caused membrane depolarization and Evans blue (30 muM) reversed 2-methoxyestradiol-induced depolarization. The present study provides evidence that 2-methoxyestradiol can suppress the activity of BKCa channels in endothelial cells. These effects of 2-methoxyestradiol on ionic currents may contribute to its effects on functional activity of endothelial cells.