Han Sol Kim

The calmodulin inhibitor and antipsychotic drug trifluoperazine inhibits voltage-dependent K+ channels in rabbit coronary arterial smooth muscle cells

We investigated the effect of the calmodulin inhibitor and antipsychotic drug trifluoperazine on voltage-dependent K(+) (Kv) channels. Kv currents were recorded by whole-cell configuration of patch clamp in freshly isolated rabbit coronary arterial smooth muscle cells. The amplitudes of Kv currents were reduced by trifluoperazine in a concentration-dependent manner, with an apparent IC50 value of 1.58±0.48 μM. The rate constants of association and dissociation by trifluoperazine were 3.73±0.33 μM(-1) s(-1) and 5.84±1.41 s(-1), respectively. Application of trifluoperazine caused a positive shift in the activation curve but had no significant effect on the inactivation curve. Furthermore, trifluoperazine provoked use-dependent inhibition of the Kv current under train pulses (1 or 2 Hz). These findings suggest that trifluoperazine interacts with Kv current in a closed state and inhibits Kv current in the open state in a time- and use-dependent manner, regardless of its function as a calmodulin inhibitor and antipsychotic drug.

The calmodulin inhibitor CGS 9343B inhibits voltage-dependent K+ channels in rabbit coronary arterial smooth muscle cells.

We investigated the effects of the calmodulin inhibitor CGS 9343B on voltage-dependent K(+) (Kv) channels using whole-cell patch clamp technique in freshly isolated rabbit coronary arterial smooth muscle cells. CGS 9343B inhibited Kv currents in a concentration-dependent manner, with a half-maximal inhibitory concentration (IC50) value of 0.81μM. The decay rate of Kv channel inactivation was accelerated by CGS 9343B. The rate constants of association and dissociation for CGS 9343B were 2.77±0.04μM(-1)s(-1) and 2.55±1.50s(-1), respectively. CGS 9343B did not affect the steady-state activation curve, but shifted the inactivation curve toward to a more negative potential. Train pulses (1 or 2Hz) application progressively increased the CGS 9343B-induced Kv channel inhibition. In addition, the inactivation recovery time constant was increased in the presence of CGS 9343B, suggesting that CGS 9343B-induced inhibition of Kv channel was use-dependent. Another calmodulin inhibitor, W-13, did not affect Kv currents, and did not change the inhibitory effect of CGS 9343B on Kv current. Our results demonstrated that CGS 9343B inhibited Kv currents in a state-, time-, and use-dependent manner, independent of calmodulin inhibition.

The Effects of the Selective Serotonin Reuptake Inhibitor Fluvoxamine on Voltage-Dependent K+ Channels in Rabbit Coronary Arterial Smooth Muscle Cells

We demonstrated the inhibitory effect of fluvoxamine, a selective serotonin reuptake inhibitor (SSRI), on voltage-dependent K(+) (Kv) channels in freshly isolated rabbit coronary arterial smooth muscle cells using a whole-cell patch clamp technique. Fluvoxamine reduced the amplitude of Kv currents in a concentration-dependent manner with an IC50 value of 3.71±1.09 µM and a Hill coefficient of 0.62±0.14. Although fluvoxamine did not significantly affect the steady-state activation curve, it shifted the steady-state inactivation curve toward a more negative potential. Pretreatment with another SSRI, paroxetine, did not affect the basal Kv current and did not alter the inhibitory effect of fluvoxamine on Kv channels. We concluded that fluvoxamine inhibits the Kv current in a concentration-dependent manner and in a closed (inactivated) state of the Kv channels independent of serotonin reuptake inhibition.

The anti-diabetic drug repaglinide induces vasorelaxation via activation of PKA and PKG in aortic smooth muscle

We investigated the vasorelaxant effect of repaglinide and its related signaling pathways using phenylephrine (Phe)-induced pre-contracted aortic rings. Repaglinide induced vasorelaxation in a concentration-dependent manner. The repaglinide-induced vasorelaxation was not affected by removal of the endothelium. In addition, application of a nitric oxide synthase inhibitor (L-NAME) and a small-conductance Ca(2+)-activated K(+) (SKCa) channel inhibitor (apamin) did not alter the vasorelaxant effect of repaglinide on endothelium-intact arteries. Pretreatment with an adenylyl cyclase inhibitor (SQ 22536) or a PKA inhibitor (KT 5720) effectively reduced repaglinide-induced vasorelaxation. Also, pretreatment with a guanylyl cyclase inhibitor (ODQ) or a PKG inhibitor (KT 5823) inhibited repaglinide-induced vasorelaxation. However, pretreatment with a voltage-dependent K(+) (Kv) channel inhibitor (4-AP), ATP-sensitive K(+) (KATP) channel inhibitor (glibenclamide), large-conductance Ca(2+)-activated K(+) (BKCa) channel inhibitor (paxilline), or the inwardly rectifying K(+) (Kir) channel inhibitor (Ba(2+)) did not affect the vasorelaxant effect of repaglinide. Furthermore, pretreatment with a Ca(2+) inhibitor (nifedipine) and a sarco-endoplasmic reticulum Ca(2+)-ATPase (SERCA) inhibitor (thapsigargin) did not affect the vasorelaxant effect of repaglinide. The vasorelaxant effect of repaglinide was not affected by elevated glucose (50mM). Based on these results, we conclude that repaglinide induces vasorelaxation via activation of adenylyl cyclase/PKA and guanylyl cyclase/PKG signaling pathways independently of the endothelium, K(+) channels, Ca(2+) channels, and intracellular Ca(2+) ([Ca(2+)]i).

Selective serotonin reuptake inhibitor sertraline inhibits voltage-dependent K + channels in rabbit coronary arterial smooth muscle cells

We examined the effects of the selective serotonin reuptake inhibitor (SSRI) sertraline on voltage-dependent K+ (Kv) channels in freshly isolated rabbit coronary arterial smooth muscle cells using the voltage-clamp technique. Sertraline decreased the Kv channel current in a dose-dependent manner, with an IC50 value of 0.18 μM and a slope value (Hill coefficient) of 0.61. Although the application of 1 μM sertraline did not affect the steady-state activation curves, sertraline caused a significant, negative shift in the inactivation curves. Pretreatment with another SSRI, paroxetine, had no significant effect on Kv currents and did not alter the inhibitory effects of sertraline on Kv currents. From these results, we concluded that sertraline dose-dependently inhibited Kv currents independently of serotonin reuptake inhibition by shifting inactivation curves to a more negative potential.

Escitalopram, a selective serotonin reuptake inhibitor, inhibits voltage-dependent K+ channels in coronary arterial smooth muscle cells.

We investigated the inhibitory effect of escitalopram, a selective serotonin reuptake inhibitor (SSRI), on voltage-dependent K+ (Kv) channels in freshly separated from rabbit coronary arterial smooth muscle cells. The application of escitalopram rapidly inhibited vascular Kv channels. Kv currents were progressively inhibited by an increase in the concentrations of escitalopram, suggesting that escitalopram inhibited vascular Kv currents in a concentration-dependent manner. The IC50 value and Hill coefficient for escitalopram-induced inhibition of Kv channels were 9.54±1.33 µM and 0.75±0.10, respectively. Addition of escitalopram did not alter the steady-state activation and inactivation curves, suggesting that the voltage sensors of the channels were not affected. Pretreatment with inhibitors of Kv1.5 and/or Kv2.1 did not affect the inhibitory action of escitalopram on vascular Kv channels. From these results, we concluded that escitalopram decreased the vascular Kv current in a concentration-dependent manner, independent of serotonin reuptake inhibition.

The selective serotonin reuptake inhibitor dapoxetine inhibits voltage-dependent K+ channels in rabbit coronary arterial smooth muscle cells

We investigated the inhibitory effect of dapoxetine, a selective serotonin reuptake inhibitor (SSRI), on voltage‐dependent K+ (Kv) channels using native smooth muscle cells from rabbit coronary arteries. Dapoxetine inhibited Kv channel currents in a concentration‐dependent manner, with an IC50 value of 2.68±0.94 μmol/L and a slope value (Hill coefficient) of 0.63±0.11. Application of 10 μmol/L dapoxetine accelerated the rate of inactivation of Kv currents. Although dapoxetine did not modify current activation kinetics, it caused a significant negative shift in the inactivation curves. Application of train step (1 or 2 Hz) progressively increased the inhibitory effect of dapoxetine on Kv channels. In addition, the recovery time constant was extended in its presence, suggesting that the longer recovery time constant from inactivation underlies a use‐dependent inhibition of the channel. From these results, we conclude that dapoxetine inhibits Kv channels in a dose‐, time‐, use‐, and state (open)‐dependent manner, independent of serotonin reuptake inhibition.

Y-27632, a Rho-Associated Protein Kinase Inhibitor, Inhibits Voltage-Dependent K+ Channels in Rabbit Coronary Arterial Smooth Muscle Cells

We examined the effects of the Rho-associated protein kinase (ROCK) inhibitor Y-27632 on voltage-dependent K+ (Kv) channels in rabbit coronary arterial smooth muscle cells using the whole-cell patch clamp technique. Y-27632 reduced the amplitude of the Kv current in a concentration-dependent manner, with an IC50 of 0.87 ± 0.06 μmol/l and a Hill coefficient of 1.48 ± 0.06. Y-27632 did not affect the steady-state activation or inactivation curves, suggesting that the drug does not affect the voltage sensitivity of Kv channels. Another ROCK inhibitor, H-1152, did not affect the Kv current and had no significant effect on the Y-27632-induced inhibition of Kv channels, indicating that the inhibitory effect of Y-27632 on the Kv current is independent of ROCK signaling. From these results, we conclude that Y-27632 inhibits the Kv channel current in a dose-dependent and ROCK signaling-independent manner.

Functional expression and pharmaceutical efficacy of cardiac-specific ion channels in human embryonic stem cell-derived cardiomyocytes

Cardiomyocytes differentiated from human pluripotent stem cells provide promising tools for screening of cardiotoxic drugs. For evaluation of human pluripotent stem cell-derived cardiomyocytes for cardiotoxicity test, in the present study, human embryonic stem cells (hESCs) were differentiated to cardiomyocytes, followed by metabolic selection to enrich the differentiated cardiomyocytes. The highly purified hESC-derived cardiomyocytes (hESC-CMs) expressed several cardiomyocyte-specific markers including cTnT, MLC2a, and α-SA, but not pluripotency markers, such as OCT4 and NANOG. Patch clamp technique and RT-PCR revealed the expression of cardiomyocyte-specific Na+, Ca2+, and K+ channels and cardiac action potential in hESC-CMs. To explore the potential use of hESC-CMs as functional cardiomyocytes for drug discovery and cardiotoxicity screening, we examined the effects of bisindolylmaleimide (BIM) (I), which inhibits native cardiac Ca2+ channels, on the Ca2+ channel activity of hESC-CMs. We observed a similar response for the BIM (I)-induced modulation of Ca2+ channels between hESC-CMs and native cardiomyocytes through L-type Ca2+ channel current. These results suggest that hESC-CMs can be useful for evaluation of pharmaceutical efficacy and safety of novel drug candidate in cardiac research.