title: Raloxifene inhibits cloned Kv4.3 channels in an estrogen receptor-independent manner.
abstract: Raloxifene is widely used for the treatment and prevention of postmenopausal osteoporosis. We examined the effects of raloxifene on the Kv4.3 currents expressed in Chinese hamster ovary (CHO) cells using the whole-cell patch-clamp technique and on the long-term modulation of Kv4.3 messenger RNA (mRNA) by real-time PCR analysis. Raloxifene decreased the Kv4.3 currents with an IC50 of 2.0 μM and accelerated the inactivation and activation kinetics in a concentration-dependent manner. The inhibitory effects of raloxifene on Kv4.3 were time-dependent: the association and dissociation rate constants for raloxifene were 9.5 μM(-1) s(-1) and 23.0 s(-1), respectively. The inhibition by raloxifene was voltage-dependent (δ = 0.13). Raloxifene shifted the steady-state inactivation curves in a hyperpolarizing direction and accelerated the closed-state inactivation of Kv4.3. Raloxifene slowed the time course of recovery from inactivation, thus producing a use-dependent inhibition of Kv4.3. β-Estradiol and tamoxifen had little effect on Kv4.3. A preincubation of ICI 182,780, an estrogen receptor antagonist, for 1 h had no effect on the inhibitory effect of raloxifene on Kv4.3. The metabolites of raloxifene, raloxifene-4'-glucuronide and raloxifene-6'-glucuronide, had little or no effect on Kv4.3. Coexpression of KChIP2 subunits did not alter the drug potency and steady-state inactivation of Kv4.3 channels. Long-term exposure to raloxifene (24 h) significantly decreased the expression level of Kv4.3 mRNA. This effect was not abolished by the coincubation with ICI 182,780. Raloxifene inhibited Kv4.3 channels by interacting with their open state during depolarization and with the closed state at subthreshold potentials. This effect was not mediated via an estrogen receptor.
authors.affiliation: Department of Physiology, College of Medicine, The Catholic University of Korea, 222 Banpo-daero, Seocho-gu, Seoul, 137-701, South Korea.
authors.forename: Yun Ju
authors.initials: YJ
authors.lastname: Chae
authors.forename: Dae Hun
authors.initials: DH
authors.lastname: Kim
authors.forename: Hong Joon
authors.initials: HJ
authors.lastname: Lee
authors.forename: Ki-Wug
authors.initials: KW
authors.lastname: Sung
authors.forename: Oh-Joo
authors.initials: OJ
authors.lastname: Kwon
authors.forename: Sang June
authors.initials: SJ
authors.lastname: Hahn
mesh_terms: D000818:Animals; D050071:Bone Density Conservation Agents / Q000494:pharmacology*; D016466:CHO Cells; D003001:Cloning, Molecular; D003412:Cricetulus; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D004958:Estradiol / Q000494:pharmacology; D004965:Estrogen Antagonists / Q000494:pharmacology; D015640:Ion Channel Gating / Q000187:drug effects; D007700:Kinetics; D051605:Kv Channel-Interacting Proteins / Q000235:genetics / Q000378:metabolism; D008564:Membrane Potentials; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers / Q000494:pharmacology*; D012333:RNA, Messenger / Q000378:metabolism; D020849:Raloxifene Hydrochloride / Q000494:pharmacology*; D060888:Real-Time Polymerase Chain Reaction; D011960:Receptors, Estrogen / Q000187:drug effects / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D051672:Shal Potassium Channels / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D013629:Tamoxifen / Q000494:pharmacology; D014162:Transfection
chemical_list: D050071:Bone Density Conservation Agents; D004965:Estrogen Antagonists; D051605:Kv Channel-Interacting Proteins; D026902:Potassium Channel Blockers; D012333:RNA, Messenger; D011960:Receptors, Estrogen; D051672:Shal Potassium Channels; D013629:Tamoxifen; D020849:Raloxifene Hydrochloride; D004958:Estradiol