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.

Open channel block of Kv1.4 potassium channels by aripiprazole

“…Kv1.4 and Kv4.3 currents were recorded using the whole-cell patch-clamp technique with a Multiclamp 700B amplifier (Molecular Devices, San Jose, CA, USA) as described previously [ 18 ]. Data acquisition was performed with pClamp 10.0 software (Axon Instruments, Inc., Forster City, CA, USA) using a digidata1322A interface (Molecular Devices).…”

Estrogen receptor beta as target for colorectal cancer prevention

“…It is not known whether it is an agonist or antagonist to either ER in the colon, but one report indicates it may be an agonist to ERβ in colon cancer cell lines [66]. Raloxifene has also been reported to have ER-independent effects, such as inhibiting the voltage-gated ion channel Kv4.3 (KCND3) [67]. At early adenoma stage, groups of rats (36 or 45 per group) were fed diets containing raloxifene (1.5 or 3 ppm), for 40 weeks.…”

“…Interestingly, the combination of Ad-ERβ + raloxifene brought about an even higher tumor volume reduction (89% vs controls, P <0.001) [66]. Possibly, the ER-independent effects of raloxifene [67] explain the raloxifene effect in the essentially ER-negative HCT116 cells, and the enhanced effect of raloxifene together with ERβ may be a consequence of its binding to and potential activation of ERβ. A follow-up study tested the therapeutic effect of combined Ad-ERβ and thermotherapy in a HCT116 colon cancer xenograft model.…”