• Proceedings of the Korean Biophysical Society Conference
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• 1999.06a
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• pp.22-23
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• 1999

Voltage-gated $K^{＋}$ channels represent the most complex group of ion channel genes expressed in cardiovascular system. The human Kv1.5 channel (hKv1.5) represents the $I_{Kur}$ repolarizing current in atrial myocytes. The hKv1.5 channel is functionally modulated by the Kv$\beta$1.3 subunit, which converts it from a delayed rectifier to a channel with rapid inactivation and enhanced voltage sensitivity.(omitted)d)

• The Korean Journal of Physiology and Pharmacology
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• v.22 no.1
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• pp.71-80
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• 2018

In patients with epilepsy, depression is a common comorbidity but difficult to be treated because many antidepressants cause pro-convulsive effects. Thus, it is important to identify the risk of seizures associated with antidepressants. To determine whether paroxetine, a very potent selective serotonin reuptake inhibitor (SSRI), interacts with ion channels that modulate neuronal excitability, we examined the effects of paroxetine on Kv3.1 potassium channels, which contribute to high-frequency firing of interneurons, using the whole-cell patch-clamp technique. Kv3.1 channels were cloned from rat neurons and expressed in Chinese hamster ovary cells. Paroxetine reversibly reduced the amplitude of Kv3.1 current, with an $IC_{50}$ value of $9.43{\mu}M$ and a Hill coefficient of 1.43, and also accelerated the decay of Kv3.1 current. The paroxetine-induced inhibition of Kv3.1 channels was voltage-dependent even when the channels were fully open. The binding ($k_{+1}$) and unbinding ($k_{-1}$) rate constants for the paroxetine effect were $4.5{\mu}M^{-1}s^{-1}$ and $35.8s^{-1}$, respectively, yielding a calculated $K_D$ value of $7.9{\mu}M$. The analyses of Kv3.1 tail current indicated that paroxetine did not affect ion selectivity and slowed its deactivation time course, resulting in a tail crossover phenomenon. Paroxetine inhibited Kv3.1 channels in a use-dependent manner. Taken together, these results suggest that paroxetine blocks the open state of Kv3.1 channels. Given the role of Kv3.1 in fast spiking of interneurons, our data imply that the blockade of Kv3.1 by paroxetine might elevate epileptic activity of neural networks by interfering with repetitive firing of inhibitory neurons.

• Archives of Pharmacal Research
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• v.28 no.3
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• pp.269-273
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• 2005

A furocoumarin derivative, psoralen (7H-furo[3,2-g][1]benzopyran-7-one), was isolated from the n-hexane fraction of Heracleum moellendorffii Hance. We examined the effects of psor-alen on a human Kv1.5 potassium channel (hKv1.5) cloned from human heart and stably expressed in Uk- cells. We found that psoralen inhibited the hKv1.5 current in a concentration-, use- and voltage-dependent manner with an IC$_{50}$ value of 180 $\pm$ 21 nM at +60 mV. Psoralen accelerated the inactivation kinetics of the hKv1.5 channel, and it slowed the deactivation kinetics of the hKv1.5 current resulting in a tail crossover phenomenon. These results indicate that psoralen acts on the hKv1.5 channel as an open channel blocker. Furthermore, psoralen prolonged the action potential duration of rat atrial muscles in a dose-dependent manner. Taken together, the present results strongly suggest that psoralen may be an ideal antiarrhythmic drug for atrial fibrillation.

• The Korean Journal of Physiology and Pharmacology
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• v.9 no.6
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• pp.353-361
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• 2005

The interaction of cyclosporine A (CsA), an immunosuppressant, with rat brain Kv1.5 (Kv1.5) channels, which were stably expressed in Chinese hamster ovary cells, was investigated using the whole-cell patch-clamp technique. CsA reversibly blocked Kv1.5 currents at +50 mV in a reversible concentrationdependent manner with an apparent $IC_{50}$ of 1.0μM. Other calcineurin inhibitors (cypermethrin, autoinhibitory peptide) had no effect on Kv1.5 and did not prevent the inhibitory effect of CsA. Fast application of CsA led to a rapid and reversible block of Kv1.5, and the onset time constants of the CsA-induced block were decreased in a concentration-dependent manner. The CsA-induced block of Kv1.5 channels was voltage-dependent, with a steep increase over the voltage range of channel opening. However, the block exhibited voltage independence over the voltage range in which channels were fully activated. The rate constants for association and dissociation of CsA were $7.0{\mu}M{-1}s^{-1}$ and $8.1s^{-1}$, respectively. CsA slowed the deactivation time course, resulting in a tail crossover phenomenon. Block of Kv1.5 by CsA was use-dependent. CsA also blocked Kv1.3 currents at +50 mV in a reversible concentration-dependent manner with an apparent $IC_{50}$ of $1.1{\mu}M$. The same effects of CsA on Kv1.3 were also observed in excised inside-out patches when applied to the internal surface of the membrane. The present results suggest that CsA acts directly on Kv1.5 currents as an open-channel blocker, independently of the effects of CsA on calcineurin activity.

• The Korean Journal of Physiology and Pharmacology
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• v.10 no.2
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• pp.71-77
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• 2006

The goal of this study was to analyze the effects of genistein, a widely used tyrosine kinase inhibitor, on cloned Shaw-type $K^+$ currents, Kv3.1 which were stably expressed in Chinese hamster ovary (CHO) cells, using the whole-cell configuration of patch-clamp techniques. In whole-cell recordings, genistein at external concentrations from 10 to $100{\mu}M$ accelerated the rate of inactivation of Kv3.1 currents, thereby concentration-dependently reducing the current at the end of depolarizing pulse with an $IC_{50}$ value of $15.71{\pm}0.67{\mu}M$ and a Hill coefficient of $3.28{\pm}0.35$ (n=5). The time constant of activation at a 300 ms depolarizing test pulses from -80 mV to +40 mV was $1.01{\pm}0.04$ ms and $0.90{\pm}0.05$ ms (n=9) under control conditions and in the presence of $20{\mu}M$ genistein, respectively, indicating that the activation kinetics was not significantly modified by genistein. Genistein $(20{\mu}M)$ slowed the deactivation of the tail current elicited upon repolarization to -40 mV, thus inducing a crossover phenomenon. These results suggest that drug unbinding is required before Kv3.1 channels can close. Genistein-induced block was voltage-dependent, increasing in the voltage range $(-20\'mV{\sim}0\'mV)$ for channel opening, suggesting an open channel interaction. Genistein $(20{\mu}M)$ produced use-dependent block of Kv3.1 at a stimulation frequency of 1 Hz. The voltage dependence of steady-state inactivation of Kv3.1 was not changed by $20{\mu}M$ genistein. Our results indicate that genistein blocks directly Kv3.1 currents in concentration-, voltage-, time-dependent manners and the action of genistein on Kv3.1 is independent of tyrosine kinase inhibition.

• The Korean Journal of Physiology and Pharmacology
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• v.26 no.5
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• pp.397-404
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• 2022

Fesoterodine, an antimuscarinic drug, is widely used to treat overactive bladder syndrome. However, there is little information about its effects on vascular K⁺ channels. In this study, voltage-dependent K⁺ (Kv) channel inhibition by fesoterodine was investigated using the patch-clamp technique in rabbit coronary artery. In whole-cell patches, the addition of fesoterodine to the bath inhibited the Kv currents in a concentration-dependent manner, with an IC₅₀ value of 3.19 ± 0.91 μM and a Hill coefficient of 0.56 ± 0.03. Although the drug did not alter the voltage-dependence of steady-state activation, it shifted the steady-state inactivation curve to a more negative potential, suggesting that fesoterodine affects the voltage-sensor of the Kv channel. Inhibition by fesoterodine was significantly enhanced by repetitive train pulses (1 or 2 Hz). Furthermore, it significantly increased the recovery time constant from inactivation, suggesting that the Kv channel inhibition by fesoterodine is use (state)-dependent. Its inhibitory effect disappeared by pretreatment with a Kv 1.5 inhibitor. However, pretreatment with Kv2.1 or Kv7 inhibitors did not affect the inhibitory effects on Kv channels. Based on these results, we conclude that fesoterodine inhibits vascular Kv channels (mainly the Kv1.5 subtype) in a concentration- and use (state)-dependent manner, independent of muscarinic receptor antagonism.

• The Korean Journal of Physiology and Pharmacology
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• v.27 no.1
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• pp.95-103
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• 2023

Rosiglitazone is a thiazolidinedione-class antidiabetic drug that reduces blood glucose and glycated hemoglobin levels. We here investigated the interaction of rosiglitazone with Kv3.1 expressed in Chinese hamster ovary cells using the wholecell patch-clamp technique. Rosiglitazone rapidly and reversibly inhibited Kv3.1 currents in a concentration-dependent manner (IC₅₀ = 29.8 µM) and accelerated the decay of Kv3.1 currents without modifying the activation kinetics. The rosiglitazonemediated inhibition of Kv3.1 channels increased steeply in a sigmoidal pattern over the voltage range of -20 to +30 mV, whereas it was voltage-independent in the voltage range above +30 mV, where the channels were fully activated. The deactivation of Kv3.1 current, measured along with tail currents, was also slowed by the drug. In addition, the steady-state inactivation curve of Kv3.1 by rosiglitazone shifts to a negative potential without significant change in the slope value. All the results with the use dependence of the rosiglitazone-mediated blockade suggest that rosiglitazone acts on Kv3.1 channels as an open channel blocker.

• The Korean Journal of Physiology and Pharmacology
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• v.20 no.1
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• pp.75-82
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• 2016

Paroxetine, a selective serotonin reuptake inhibitor (SSRI), has been reported to have an effect on several ion channels including human ether-a-go-go-related gene in a SSRI-independent manner. These results suggest that paroxetine may cause side effects on cardiac system. In this study, we investigated the effect of paroxetine on Kv1.5, which is one of cardiac ion channels. The action of paroxetine on the cloned neuronal rat Kv1.5 channels stably expressed in Chinese hamster ovary cells was investigated using the whole-cell patch-clamp technique. Paroxetine reduced Kv1.5 whole-cell currents in a reversible concentration-dependent manner, with an $IC_{50}$ value and a Hill coefficient of $4.11{\mu}M$ and 0.98, respectively. Paroxetine accelerated the decay rate of inactivation of Kv1.5 currents without modifying the kinetics of current activation. The inhibition increased steeply between -30 and 0 mV, which corresponded with the voltage range for channel opening. In the voltage range positive to 0 mV, inhibition displayed a weak voltage dependence, consistent with an electrical distance ${\delta}$ of 0.32. The binding ($k_{+1}$) and unbinding ($k_{-1}$) rate constants for paroxetine-induced block of Kv1.5 were $4.9{\mu}M^{-1}s^{-1}$ and $16.1s^{-1}$, respectively. The theoretical $K_D$ value derived by $k_{-1}/k_{+1}$ yielded $3.3{\mu}M$. Paroxetine slowed the deactivation time course, resulting in a tail crossover phenomenon when the tail currents, recorded in the presence and absence of paroxetine, were superimposed. Inhibition of Kv1.5 by paroxetine was use-dependent. The present results suggest that paroxetine acts on Kv1.5 currents as an open-channel blocker.

• BMB Reports
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• v.42 no.8
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• pp.535-539
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• 2009

Voltage-gated $K^+$ (Kv) channels are widely expressed in the plasma membranes of numerous cells such as epithelial cells. Recently, it has been demonstrated that Kv channels are associated with the proliferation of several types of cancer cells. Specifically, Kv1.3 seems to be involved in cancer cell proliferation and apoptosis. In the present study, we examined the expression of Kv1.3 in immortalized and tumorigenic human mammary epithelial cells. We also evaluated the expression level of Kv1.3 in each stage of breast cancer using mRNA isolated from breast cancer patients. In addition, treatment with tetraethylammonium, a Kv channel blocker, suppressed tumorigenic human mammary epithelial cell proliferation. Therefore, Kv1.3 may serve as a novel molecular target for breast cancer therapy while its stage-specific expression pattern may provide a potential diagnostic marker for breast cancer development.

• BMB Reports
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• v.43 no.11
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• pp.756-760
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• 2010

Recent studies have reported that delayed-rectifier Kv channels regulate apoptosis in the nervous system. Herein, we investigated changes in the expression of the delayed-rectifier Kv channels Kv1.2, Kv2.1, and Kv3.1 after acute spinal cord injury (SCI) in rats. We performed RT-PCR analysis and found an increase in the level of Kv2.1 mRNA after SCI but no significant changes in the levels of Kv1.2 and Kv3.1 mRNA. Western blot analysis revealed that Kv2.1 protein levels rapidly decreased and then dramatically increased from 1 day, whereas Kv3.1b protein levels gradually and sharply decreased at 5 days. Kv1.2 protein levels did not change significantly. In addition, Kv2.1 clusters were disrupted in the plasma membranes of motor neurons after SCI. Interestingly, the expressional changes and translocation of Kv2.1 were consistent with the apoptotic changes on day 1. Therefore, these results suggest that Kv2.1 channels probably contribute to neuronal cell responses to SCI.