title: 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 17beta-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 microm) reversibly suppressed the amplitude of K+ outward currents. The IC50 value of the 2-methoxyestradiol-induced decrease in outward current was 3 microm. Evans blue (30 microm) or niflumic acid (30 microm), but not diazoxide (30 microm), reversed the 2-methoxyestradiol-induced decrease in outward current. In the inside-out configuration, application of 2-methoxyestradiol (3 microm) 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 microm) 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 17beta-estradiol (10 microm) nor estriol (10 microm) affected BKCa channel activity, whereas 2-hydroxyestradiol (10 microm) slightly suppressed it. Under current-clamp condition, 2-methoxyestradiol (10 microm) caused membrane depolarization and Evans blue (30 microm) 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.
authors.affiliation: Department of Internal Medicine, Kaohsiung Veterans General Hospital, No. 386, Ta-Chung 1st Rd, Kaohsiung City, Taiwan.
authors.forename: H T
authors.initials: HT
authors.lastname: Chiang
authors.forename: S N
authors.initials: SN
authors.lastname: Wu
mesh_terms: D000077584:2-Methoxyestradiol; D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D002460:Cell Line; D003981:Diazoxide / Q000494:pharmacology; D004347:Drug Interactions; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D004958:Estradiol / Q000031:analogs & derivatives* / Q000494:pharmacology*; D004964:Estriol / Q000494:pharmacology; D005070:Evans Blue / Q000494:pharmacology; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D051036:Large-Conductance Calcium-Activated Potassium Channels; D008564:Membrane Potentials / Q000502:physiology; D009544:Niflumic Acid / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010455:Peptides / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000378:metabolism; D024681:Potassium Channels, Calcium-Activated; D014665:Vasodilator Agents / Q000494:pharmacology
chemical_list: D007211:Indoles; D051036:Large-Conductance Calcium-Activated Potassium Channels; D010455:Peptides; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D014665:Vasodilator Agents; D015124:8-Bromo Cyclic Adenosine Monophosphate; C048220:paxilline; D005070:Evans Blue; D004958:Estradiol; D009544:Niflumic Acid; D000077584:2-Methoxyestradiol; C064719:iberiotoxin; C001390:2-hydroxyestradiol; D004964:Estriol; D003981:Diazoxide; D011188:Potassium