2-Methoxyestradiol, an endogenous metabolite of 17 beta -estradiol, is know
n to have antitumor and antiangiogenic actions. The effects of 2-methoxyest
radiol on ionic currents were investigated in an endothelial cell line (HUV
-EC-C) originally derived from human umbilical vein. In the whole-cell patc
h-clamp configuration, 2-methoxyestradiol (0.3-30 muM) reversibly suppresse
d the amplitude of K+ outward currents. The IC50 value of the 2-methoxyestr
adiol-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-methoxy
estradiol-induced decrease in outward current. In the inside-out configurat
ion, application of 2-methoxyestradiol (3 muM) to the bath did not modify t
he single-channel conductance of large-conductance Ca2+ activated K+ (BKCa)
channels; however, it did suppress the channel activity. 2-Methoxyestradio
l (3 muM) produced a shift in the activation curve of BKCa channels to more
positive potentials. Kinetic studies showed that the 2-methoxyestradiol-in
duced inhibition of BKCa channels is primarily mediated by a decrease in th
e number of long-lived openings. 2-Methoxyestradiol-induced inhibition of t
he channel activity was potentiated by membrane stretch. In contrast, neith
er 17 beta -estradiol (10 muM) nor estriol (10 muM) affected BKCa channel a
ctivity, whereas 2-hydroxyestradiol (10 muM) slightly suppressed it. Under
current-clamp condition, 2-methoxyestradiol (10 muM) caused membrane depola
rization and Evans blue (30 muM) reversed 2-methoxyestradiol-induced depola
rization. The present study provides evidence that 2-methoxyestradiol can s
uppress the activity of BKCa channels in endothelial cells. These effects o
f 2-methoxyestradiol on ionic currents may contribute to its effects on fun
ctional activity of endothelial cells.