Mi n Seo

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 vasorelaxant effect of mitiglinide via activation of voltage-dependent K+ channels and SERCA pump in aortic smooth muscle

AIMS The vasorelaxant effects of the anti-diabetic drug, mitiglinide in phenylephrine (Phe)-pre-contracted aortic rings were examined. MATERIALS AND METHODS Arterial tone measurement was performed in aortic smooth muscle cells. KEY FINDINGS Mitiglinide dose-dependently induced vasorelaxation. Application of the large-conductance Ca2+-activated K+ (BKCa) channel blocker paxilline, inwardly rectifying K+ (Kir) channel blocker Ba2+, and ATP-sensitive K+ (KATP) channel blocker glibenclamide did not affect the vasorelaxant effect of mitiglinide. However, application of the voltage-dependent K+ (Kv) channel blocker 4-AP, effectively inhibited mitiglinide-induced vasorelaxation. Although pretreatment with the Ca2+ channel blocker nifedipine did not alter the mitiglinide-induced vasorelaxation, pretreatment with the sarcoplasmic/endoplasmic reticulum Ca2+-ATPase (SERCA) pump inhibitor thapsigargin and cyclopiazonic acid reduced the vasorelaxant effect of mitiglinide. In addition, the vasorelaxant effect of mitiglinide was not affected by the inhibitors of adenylyl cyclase, protein kinase A, guanylyl cyclase, or protein kinase G. Elimination of the endothelium and inhibition of endothelium-dependent vasorelaxant mechanisms also did not change the vasorelaxant effect of mitiglinide. SIGNIFICANCE We proposed that mitiglinide induces vasorelaxation via activation of Kv channels and SERCA pump. However, the vasorelaxant effects of mitiglinide did not involve other K+ channels, Ca2+ channels, PKA/PKG signaling pathways, or the endothelium.

The anti-diabetic drug dapagliflozin induces vasodilation via activation of PKG and Kv channels

Aim: Considering the clinical efficacy of dapagliflozin in patients with type 2 DM and the pathophysiological relevance of Kv channels for vascular reactivity. We investigate the vasodilatory effect of dapagliflozin and related mechanisms using phenylephrine (Phe)‐induced contracted aortic rings. Material and methods: Arterial tone measurement was performed in aortic smooth muscle. Key findings: Application of dapagliflozin induced vasodilation in a concentration‐dependent manner. Pre‐treatment with the BKCa channel inhibitor paxilline, the KATP channel inhibitor glibenclamide, and the Kir channel inhibitor Ba2+ did not change dapagliflozin‐induced vasodilation. However, application of the Kv channels inhibitor 4‐AP effectively inhibited dapagliflozin‐induced vasodilation. Application of the Ca2+ channel inhibitor nifedipine and the sarcoplasmic/endoplasmic reticulum Ca2+‐ATPase (SERCA) pump inhibitor thapsigargin did not alter the vasodilatory effect of dapagliflozin. Moreover, the adenylyl cyclase inhibitor SQ 22536 and the protein kinase A (PKA) inhibitor KT 5720 had no effect on dapagliflozin‐induced vasodilation. Although guanylyl cyclase inhibitors, NS 2028 and ODQ, did not reduce the vasodilatory effect of dapagliflozin, the protein kinase G (PKG) inhibitor KT 5823 effectively inhibited dapagliflozin‐induced vasodilation. The vasodilatory effect of dapagliflozin was not affected by elimination of the endothelium. Furthermore, pretreatment with the nitric oxide synthase inhibitor L‐NAME or the small‐conductance Ca2+‐activated K (SKCa) channel inhibitor apamin did not change the vasodilatory effect of dapagliflozin. Significance: We concluded that dapagliflozin induced vasodilation via the activation of Kv channels and PKG, and was independent of other K+ channels, Ca2+ channels, intracellular Ca2+, and the endothelium.

The vasorelaxant effect of anti‐diabetic drug nateglinide via activation of voltage‐dependent K+ channels in aortic smooth muscle

AIMS We investigated the vasorelaxant effect of nateglinide and its related mechanisms using phenylephrine (Phe)-induced precontracted aortic rings. METHODS Arterial tone measurement was performed in aortic smooth muscle. RESULTS The application of nateglinide induced vasorelaxation in a concentration-dependent manner. Pretreatment with the large-conductance Ca2+ -activated K+ (BKCa ) channel inhibitor paxilline, the inwardly rectifying K+ (Kir) channel inhibitor Ba2+ , and ATP-sensitive K+ (KATP ) channel inhibitor glibenclamide did not affect the vasorelaxant effect of nateglinide. However, pretreatment with the voltage-dependent K+ (Kv) channel inhibitor 4-aminopyridine (4-AP) effectively reduced the vasorelaxant effect of nateglinide. Pretreatment with the Ca2+ inhibitor nifedipine and the sarcoplasmic/endoplasmic reticulum Ca2+ -ATPase inhibitor thapsigargin did not change the vasorelaxant effect of nateglinide. Additionally, the vasorelaxant effect of nateglinide was not altered in the presence of an adenylyl cyclase, a protein kinase A, a guanylyl cyclase, or a protein kinase G inhibitor. The vasorelaxant effect of nateglinide was not affected by the elimination of the endothelium. In addition, pretreatment with a nitric oxide synthase inhibitor, L-NAME, and a small-conductance Ca2+ -activated K+ (SKCa ) channel inhibitor, apamin, did not change the vasorelaxant effect of nateglinide. CONCLUSION Nateglinide induced vasorelaxation via the activation of the Kv channel independent of other K+ channels, Ca2+ channels, intracellular Ca2+ ([Ca2+ ]i ), and the endothelium.

Inhibition of voltage-dependent K+ current in rabbit coronary arterial smooth muscle cells by the class Ic antiarrhythmic drug propafenone

In this study, we demonstrated the inhibitory effect of the Class Ic antiarrhythmic agent propafenone on voltage-dependent K+ (Kv) channels using freshly isolated coronary artery smooth muscle cells from rabbits. The Kv current amplitude was progressively inhibited by propafenone in a dose-dependent manner, with an apparent IC50 value of 5.04±1.05 µM and a Hill coefficient of 0.78±0.06. The application of propafenone had no significant effect on the steady-state activation and inactivation curves, indicating that propafenone did not affect the voltage-sensitivity of Kv channels. The application of train pulses at frequencies of 1 or 2 Hz progressively increased the propafenone-induced inhibition of the Kv current. Furthermore, the inactivation recovery time constant was increased after the application of propafenone, suggesting that the inhibitory action of propafenone on Kv current is partially use-dependent. Pretreatment with Kv1.5, Kv2.1 or Kv7 inhibitor did not change the inhibitory effect of propafenone on the Kv current. Together, these results suggest that propafenone inhibits the vascular Kv channels in a dose- and use-dependent manner, regardless of Na+ channel inhibition.

Inhibition of the voltage-dependent K+ current by the class Ic antiarrhythmic drug flecainide in rabbit coronary arterial smooth muscle cells

This study examined the inhibitory effect of flecainide, a class 1c antiarrhythmic agent (Na+ channel blocker), on voltage‐dependent K+ (Kv) channels in smooth muscle cells isolated from coronary arteries. Flecainide decreased the vascular Kv channel current in a dose‐dependent manner with an IC50 value of 5.90 ± 0.87 μmol/L and a Hill coefficient of 0.77 ± 0.06. Although the steady‐state activation curve was not affected by flecainide, it shifted the steady‐state inactivation curves toward a more negative potential. Application of train pulses such as 1 or 2 Hz did not change the flecainide‐induced inhibition of Kv channels, indicating that the inhibitory effect of flecainide was not use‐dependent. Using perforated‐patch clamp experiments, we found that inhibition of Kv channels by flecainide caused membrane depolarization. Together, these results suggest that flecainide inhibits Kv channels in a concentration‐dependent, but not use‐dependent manner by changing the inactivation gating properties. Furthermore, Kv channel inhibition by flecainide occurs regardless of Na+ channel inhibition.

Inhibitory effect of the tricyclic antidepressant amitriptyline on voltage-dependent K+ channels in rabbit coronary arterial smooth muscle cells

Amitriptyline, a tricyclic antidepressant (TCA) drug, is widely used in treatment of psychiatric disorders. However, the side effects of amitriptyline on vascular K+ channels remain to be determined. Therefore, we investigated the effect of the tricyclic antidepressant and serotonin reuptake inhibitor amitriptyline on voltage‐dependent K+ (Kv) channels in freshly isolated rabbit coronary arterial smooth muscle cells, using the whole‐cell patch clamp technique. The Kv current amplitudes were inhibited by amitriptyline in a concentration‐dependent manner, with an apparent IC50 value of 2.2 ± 0.14 μmol/L and a Hill coefficient of 0.87 ± 0.03. Amitriptyline shifted the activation curve to a more positive potential, but had no significant effect on the inactivation curve, suggesting that amitriptyline altered the voltage sensitivity of Kv channels. Pretreatment with Kv1.5 and Kv1.2 channel inhibitors did not alter the inhibitory effect of amitriptyline on Kv channels. Additionally, application of train pulses (1 and 2 Hz) did not affect amitriptyline‐induced inhibition of Kv currents, which suggested that the action of amitriptyline on Kv channels was not use (state)‐dependent. From these results, we concluded that amitriptyline inhibited the channels in a concentration‐dependent, but state‐independent manner.

The PPARα activator fenofibrate inhibits voltage-dependent K+ channels in rabbit coronary arterial smooth muscle cells

&NA; We examined the effects of the PPAR&agr; activator fenofibrate on voltage‐dependent K+ (Kv) channels using a patch clamp technique in native rabbit coronary arterial smooth muscle cells. Kv current was inhibited by application of fenofibrate in a concentration‐dependent manner, with an apparent IC50 value of 6.39 ± 0.53 &mgr;M and a slope value (Hill coefficient) of 1.63 ± 0.10. Fenofibrate accelerated the decay rate of Kv channel inactivation. The rate constants of association and dissociation for fenofibrate were 0.81± 0.05 &mgr;M−1 s−1 and 4.70 ± 0.47 s−1, respectively. Although fenofibrate did not affect the steady‐state activation curves, fenofibrate shifted the inactivation curves toward a more negative potential. Application of train pulses (1 or 2 Hz) progressively increased the fenofibrate‐induced inhibition of the Kv channel, and the recovery time constant from inactivation was increased in the presence of fenofibrate, which suggested that the inhibitory effect of fenofibrate is use‐dependent. Another PPAR&agr; activator, bezafibrate and PPAR&agr; inhibitor, GW 6471, did not affect the Kv current and also did not change the inhibitory effect of fenofibrate on the Kv current. From these results, we suggest that fenofibrate inhibited Kv current in a state‐, time‐, and use‐dependent manner, completely independent of PPAR&agr; activation.