Pathophysiology of voltage-gated K+ channels in vascular smooth muscle cells: Modulation by protein kinases

Vasorelaxant mechanisms of the antidiabetic anagliptin in rabbit aorta: roles of Kv channels and SERCA pump

AIMS

The present study investigated the vasorelaxant mechanisms of an oral antidiabetic drug, anagliptin, using phenylephrine (Phe)-induced pre-contracted rabbit aortic rings.

METHODS

Arterial tone measurement was performed in rabbit thoracic aortic rings.

RESULTS

Anagliptin induced vasorelaxation in a dose-dependent manner. Pre-treatment with the classical voltagedependent K+ (Kv) channel inhibitors 4-aminopyridine and tetraethylammonium significantly decreased the vasorelaxant effect of anagliptin, whereas pre-treatment with the inwardly rectifying K+ (Kir) channel inhibitor Ba2+, the ATP-sensitive K+ (KATP) channel inhibitor glibenclamide, and the large-conductance Ca2+-activated K+ (BKCa) channel inhibitor paxilline did not attenuate the vasorelaxant effect. Furthermore, the vasorelaxant response of anagliptin was effectively inhibited by pre-treatment with the sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) pump inhibitors thapsigargin and cyclopiazonic acid. Neither cAMP/protein kinase A (PKA)-related signaling pathway inhibitors (adenylyl cyclase inhibitor SQ 22536 and PKA inhibitor KT 5720) nor cGMP/protein kinase G (PKG)-related signaling pathway inhibitors (guanylyl cyclase inhibitor ODQ and PKG inhibitor KT 5823) reduced the vasorelaxant effect of anagliptin. Similarly, the anagliptin-induced vasorelaxation was independent of the endothelium.

CONCLUSIONS

Based on these results, we suggest that anagliptin-induced vasorelaxation in rabbit aortic smooth muscle occurs by activating Kv channels and the SERCA pump, independent of other vascular K+ channels, cAMP/PKA- or cGMP/PKG-related signaling pathways, and the endothelium.

Proteome landscape and interactome of voltage-gated potassium channel 1.6 (Kv1.6) of the murine ophthalmic artery and neuroretina

The voltage-gated potassium channel 1.6 (Kv1.6) plays a vital role in ocular neurovascular beds and exerts its modulatory functions via interaction with other proteins. However, the interactome and their potential roles remain unknown. Here, the global proteome landscape of the ophthalmic artery (OA) and neuroretina was mapped, followed by the determination of Kv1.6 interactome and validation of its functionality and cellular localization. Microfluorimetric analysis of intracellular [K+] and Western blot validated the native functionality and cellular expression of the recombinant Kv1.6 channel protein. A total of 54, 9 and 28 Kv1.6-interacting proteins were identified in the mouse OA and, retina of mouse and rat, respectively. The Kv1.6-protein partners in the OA, namely actin cytoplasmic 2, alpha-2-macroglobulin and apolipoprotein A-I, were implicated in the maintenance of blood vessel integrity by regulating integrin-mediated adhesion to extracellular matrix and Ca2+ flux. Many retinal protein interactors, particularly the ADP/ATP translocase 2 and cytoskeleton protein tubulin, were involved in endoplasmic reticulum stress response and cell viability. Three common interactors were found in all samples comprising heat shock cognate 71 kDa protein, Ig heavy constant gamma 1 and Kv1.6 channel. This foremost in-depth investigation enriched and identified the elusive Kv1.6 channel and, elucidated its complex interactome.

Insights into SGLT2 inhibitor treatment of diabetic cardiomyopathy: focus on the mechanisms

Among the complications of diabetes, cardiovascular events and cardiac insufficiency are considered two of the most important causes of death. Experimental and clinical evidence supports the effectiveness of SGLT2i for improving cardiac dysfunction. SGLT2i treatment benefits metabolism, microcirculation, mitochondrial function, fibrosis, oxidative stress, endoplasmic reticulum stress, programmed cell death, autophagy, and the intestinal flora, which are involved in diabetic cardiomyopathy. This review summarizes the current knowledge of the mechanisms of SGLT2i for the treatment of diabetic cardiomyopathy.

Inhibition of voltage-dependent K+ channels by antimuscarinic drug fesoterodine in coronary arterial smooth muscle cells

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.

Ion channel molecular complexes in vascular smooth muscle

Ion channels that influence membrane potential and intracellular calcium concentration control vascular smooth muscle excitability. Voltage-gated calcium channels (VGCC), transient receptor potential (TRP) channels, voltage (K_V), and Ca²⁺-activated K⁺ (BK) channels are key regulators of vascular smooth muscle excitability and contractility. These channels are regulated by various signaling cues, including protein kinases and phosphatases. The effects of these ubiquitous signaling molecules often depend on the formation of macromolecular complexes that provide a platform for targeting and compartmentalizing signaling events to specific substrates. This manuscript summarizes our current understanding of specific molecular complexes involving VGCC, TRP, and K_V and BK channels and their contribution to regulating vascular physiology.

Carbon monoxide activation of delayed rectifier potassium currents of human cardiac fibroblasts through diverse pathways

To identify the effect and mechanism of carbon monoxide (CO) on delayed rectifier K⁺ currents (I_K) of human cardiac fibroblasts (HCFs), we used the wholecell mode patch-clamp technique. Application of CO delivered by carbon monoxidereleasing molecule-3 (CORM3) increased the amplitude of outward K⁺ currents, and diphenyl phosphine oxide-1 (a specific I_K blocker) inhibited the currents. CORM3- induced augmentation was blocked by pretreatment with nitric oxide synthase blockers (L-NG-monomethyl arginine citrate and L-NG-nitro arginine methyl ester). Pretreatment with KT5823 (a protein kinas G blocker), 1H-[1,-2,-4] oxadiazolo-[4,-3-a] quinoxalin-1-on (ODQ, a soluble guanylate cyclase blocker), KT5720 (a protein kinase A blocker), and SQ22536 (an adenylate cyclase blocker) blocked the CORM3 stimulating effect on I_K. In addition, pretreatment with SB239063 (a p38 mitogen-activated protein kinase [MAPK] blocker) and PD98059 (a p44/42 MAPK blocker) also blocked the CORM3's effect on the currents. When testing the involvement of S-nitrosylation, pretreatment of N-ethylmaleimide (a thiol-alkylating reagent) blocked CO-induced I_K activation and DL-dithiothreitol (a reducing agent) reversed this effect. Pretreatment with 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)-21H,23H porphyrin manganese (III) pentachloride and manganese (III) tetrakis (4-benzoic acid) porphyrin chloride (superoxide dismutase mimetics), diphenyleneiodonium chloride (an NADPH oxidase blocker), or allopurinol (a xanthine oxidase blocker) also inhibited CO-induced I_K activation. These results suggest that CO enhances I_K in HCFs through the nitric oxide, phosphorylation by protein kinase G, protein kinase A, and MAPK, S-nitrosylation and reduction/oxidation (redox) signaling pathways.

Mechanisms underlying the vasodilatory effects of canagliflozin in the rabbit thoracic aorta: Involvement of the SERCA pump and Kv channels

AIMS

Canagliflozin is an anti-diabetic agent and sodium glucose co-transporter-2 inhibitor. Despite numerous clinical trials demonstrating its beneficial effects on blood pressure, the cellular mechanisms underlying the effects of canagliflozin on vascular reactivity have yet to be clarified. We investigated the vasodilatory effect of canagliflozin on aortic rings isolated from rabbits.

MAIN METHODS

We used rabbit thoracic aortic rings and its arterial tone was tested by using wire myography system.

KEY FINDINGS

Canagliflozin caused concentration-dependent vasodilation in aortic rings pre-constricted with phenylephrine or high K⁺. However, the degree of canagliflozin-induced vasodilation of the aortic rings pre-constricted with high K⁺ was less than that of rings pre-constricted with phenylephrine. Application of 4-aminopyridine, a voltage-dependent K⁺ (Kv) channel inhibitor, reduced canagliflozin-induced vasodilation. However, pre-incubation of an inwardly rectifying K⁺ channel inhibitor, a large-conductance Ca²⁺-activated K⁺ channel inhibitor, and an ATP-sensitive K⁺ inhibitor did not modulate the vasodilatory effects of canagliflozin. Indeed, canagliflozin increased Kv currents in aortic smooth muscle cells. Pre-treatment with thapsigargin or cyclopiazonic acid, a sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA) pump inhibitors, reduced the vasodilatory effects of canagliflozin. Conversely, pre-treatment with a Ca²⁺ channel inhibitor, adenylyl cyclase/PKA inhibitors, and guanylyl cyclase/PKG inhibitors did not modulate the vasodilatory effects of canagliflozin. Endothelium removal, and pre-treatment with the nitric oxide synthase inhibitor L-NAME, and small- and intermediate-conductance Ca²⁺-activated K⁺ channel inhibitor apamin and TRAM-34, did not diminish the vasodilatory effects of canagliflozin.

SIGNIFICANCE

Our results indicate that canagliflozin induces vasodilation, which is dependent on the robust SERCA activity and Kv channel activation.

Inhibitory effect of the selective serotonin reuptake inhibitor paroxetine on human Kv1.3 channels

Paroxetine is one of the most effective selective serotonin reuptake inhibitors used to treat depressive and panic disorders that reduce the viability of human T lymphocytes, in which Kv1.3 channels are highly expressed. We examined whether paroxetine could modulate human Kv1.3 channels acutely and directly with the aim of understanding the biophysical effects and the underlying mechanisms of the drug. Kv1.3 channel proteins were expressed in Xenopus oocytes. Paroxetine rapidly inhibited the steady-state current and peak current of these channels within 6 min in a concentration-dependent manner; IC₅₀s were 26.3 μM and 53.9 μM, respectively, and these effects were partially reversed by washout, which excluded the possibility of genomic regulation. At the same test voltage, paroxetine blockade of the steady-state currents was higher than that of the peak currents, and the inhibition of the steady-state current increased relative to the degree of depolarization. Paroxetine decreased the inactivation time constant in a concentration-dependent manner, but it did not affect the activation time constant, which resulted in the acceleration of intrinsic inactivation without changing ultrarapid activation. Blockade of Kv1.3 channels by paroxetine exhibited more rapid inhibition at higher activation frequencies showing the use-dependency of the blockade. Overall, these results show that paroxetine directly suppresses human Kv1.3 channels in an open state and accelerates the process of steady-state inactivation; thus, we have revealed a biophysical mechanism for possible acute immunosuppressive effects of paroxetine.

The anti-diabetic drug trelagliptin induces vasodilation via activation of Kv channels and SERCA pumps

AIMS

In this study, we investigated the vasodilatory effects of trelagliptin (a dipeptidyl peptidase-4 inhibitor) and its related mechanisms using rabbit aortic rings.

MAIN METHODS

Arterial tone measurement was performed in rabbit thoracic aortic rings.

KEY FINDINGS

Trelagliptin induced vasodilation in a dose-dependent manner. Pretreatment with the ATP-sensitive K⁺ channel inhibitor glibenclamide, large-conductance Ca²⁺-activated K⁺ channel inhibitor paxilline, and inwardly rectifying K⁺ channel inhibitor Ba²⁺ did not affect the vasodilatory effect of trelagliptin. However, pretreatment with the voltage-dependent K⁺ (Kv) channel inhibitors 4-aminopyridine and tetraethylammonium significantly attenuated the vasodilatory effect of trelagliptin, suggesting that the vasodilatory effect of trelagliptin is associated with Kv channel activation. Although pretreatment with Kv1.5 and Kv2.1 subtype inhibitors did not affect the response to trelagliptin, pretreatment with a Kv7.X subtype inhibitor effectively reduced the vasodilatory effect of trelagliptin. Furthermore, sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA) pump inhibitors also significantly attenuated the vasodilatory effect of trelagliptin. These effects, however, were not affected by pretreatment with Ca²⁺ channel inhibitors, adenylyl cyclase/PKA inhibitors, guanylyl cyclase/PKG inhibitors, or removal of the endothelium.

SIGNIFICANCE

From these results, we concluded that the vasodilatory effect of trelagliptin was associated with the activation of Kv channels (primary the Kv7.X subtype) and SERCA pump regardless of other K⁺ channels, Ca²⁺ channels, cAMP/PKA-related or cGMP/PKG-related signaling pathways, and the endothelium. Therefore, caution is required when prescribing trelagliptin to the patients with hypotension and diabetes.

Atypical antipsychotic olanzapine inhibits voltage-dependent K+ channels in coronary arterial smooth muscle cells

BACKGROUND

Olanzapine, an FDA-approved atypical antipsychotic, is widely used to treat schizophrenia and bipolar disorder. In this study, the inhibitory effect of olanzapine on voltage-dependent K⁺ (Kv) channels in rabbit coronary arterial smooth muscle cells was investigated.

METHODS

Electrophysiological recordings were performed in freshly isolated coronary arterial smooth muscle cells.

RESULTS

Olanzapine inhibited the Kv channels in a concentration-dependent manner with an IC₅₀ value of 7.76 ± 1.80 µM and a Hill coefficient of 0.82 ± 0.09. Although olanzapine did not change the steady-state activation curve, it shifted the inactivation curve to a more negative potential, suggesting that it inhibited Kv currents by affecting the voltage sensor of the Kv channel. Application of 1 or 2 Hz train pulses did not affect the olanzapine-induced inhibition of Kv channels, suggesting that its effect on Kv channels occurs in a use (state)-independent manner. Pretreatment with DPO-1 (Kv1.5 subtype inhibitor) reduced the olanzapine-induced inhibition of Kv currents. In addition, pretreatment with guangxitoxin (Kv2.1 subtype inhibitor) and linopirdine (Kv7 subtype inhibitor) partially decreased the degree of Kv current inhibition. Olanzapine induced membrane depolarization.

CONCLUSION

From these results, we suggest that olanzapine inhibits the Kv channels in a concentration-dependent, but state-independent, manner by affecting the gating properties of Kv channels. The primary Kv channel target of olanzapine is the Kv1.5 subtype.

Inhibition of voltage-dependent K+ channels in rabbit coronary arterial smooth muscle cells by the class Ic antiarrhythmic agent lorcainide

Voltage-dependent K⁺ (Kv) channels play the role of returning the membrane potential to the resting state, thereby maintaining the vascular tone. Here, we used native smooth-muscle cells from rabbit coronary arteries to investigate the inhibitory effect of lorcainide, a class Ic antiarrhythmic agent, on Kv channels. Lorcainide inhibited Kv channels in a concentration-dependent manner with an IC₅₀ of 4.46 ± 0.15 μM and a Hill coefficient of 0.95 ± 0.01. Although application of lorcainide did not change the activation curve, it shifted the inactivation curve toward a more negative potential, implying that lorcainide inhibits Kv channels by changing the channels' voltage sensors. The recovery time constant from channel inactivation increased in the presence of lorcainide. Furthermore, application of train steps (of 1 or 2 Hz) in the presence of lorcainide progressively augmented the inhibition of Kv currents, implying that lorcainide-induced inhibition of Kv channels is use (state)-dependent. Pretreatment with Kv1.5 or Kv2.1/2.2 inhibitors effectively reduced the amplitude of the Kv current but did not affect the inhibitory effect of lorcainide. Based on these results, we conclude that lorcainide inhibits vascular Kv channels in a concentration and use (state)-dependent manner by changing their inactivation gating properties. Considering the clinical efficacy of lorcainide, and the pathophysiological significance of vascular Kv channels, our findings should be considered when prescribing lorcainide to patients with arrhythmia and vascular disease.

The effects of tegaserod, a gastrokinetic agent, on voltage-gated K+ channels in rabbit coronary arterial smooth muscle cells

Tegaserod, a gastroprokinetic agent, is used to treat irritable bowel syndrome. Despite its extensive clinical use, little is known about the effects of tegaserod on vascular ion channels, especially K+ channels. Therefore, we examined the effects of tegaserod on voltage-gated K+ (Kv) channels in rabbit coronary arterial smooth muscle cells using the whole-cell patch-clamp technique. Tegaserod inhibited Kv channels in a concentration-dependent manner with an IC50 value of 1.26 ± 0.31 µmol/L and Hill coefficient of 0.81 ± 0.10. Although tegaserod had no effect on the steady-state activation curves of the Kv channels, the steady-state inactivation curve was shifted toward a more negative potential. These results suggest that tegaserod inhibits Kv channels by influencing their voltage sensors. The recovery time constant of channel inactivation was extended in the presence of tegaserod. Furthermore, application of train steps (1 and 2 Hz) in the presence of tegaserod progressively increased the inhibition of Kv currents suggesting that tegaserod-induced Kv channel inhibition is use (state)-dependent. Pretreatment with a Kv1.5 subtype inhibitor suppressed the Kv current. However, additional application of tegaserod did not induce further inhibition. Pretreatment with a Kv2.1 or Kv7 inhibitor did not affect the inhibitory effect of tegaserod on Kv channels. Based on these results, we conclude that tegaserod inhibits vascular Kv channels in a concentration- and use (state)-dependent manner independent of its own functions. Furthermore, the major Kv channel target of tegaserod is the Kv1.5 subtype.

Braylin induces a potent vasorelaxation, involving distinct mechanisms in superior mesenteric and iliac arteries of rats

Arterial hypertension is a risk factor for various cardiovascular and renal diseases, representing a major public health challenge. Although a wide range of treatment options are available for blood pressure control, many hypertensive individuals remain with uncontrolled hypertension. Thus, the search for new substances with antihypertensive potential becomes necessary. Coumarins, a group of polyphenolic compounds derived from plants, have attracted intense interest due to their diverse pharmacological properties, like potent antihypertensive activities. Braylin (6-methoxyseselin) is a coumarin identified in the Zanthoxylum tingoassuiba species, described as a phosphodiesterase-4 (PDE4) inhibitor. Although different coumarin compounds have been described as potent antihypertensive agents, the activity of braylin on the cardiovascular system has yet to be investigated. To investigate the vasorelaxation properties of braylin and its possible mechanisms of action, we performed in vitro studies using superior mesenteric arteries and the iliac arteries isolated from rats. In this study, we demonstrated, for the first time, that braylin induces potent vasorelaxation, involving distinct mechanisms from two different arteries, isolated from rats. A possible inhibition of phosphodiesterase, altering the cyclic adenosine monophosphate (cAMP)/cAMP-dependent protein kinase (PKA) pathway, may be correlated with the biological action of braylin in the mesenteric vessel, while in the iliac artery, the biological action of braylin may be correlated with increase of cyclic guanosine monophosphate (cGMP), followed by BKCa, Kir, and Kv channel activation. Together, these results provide evidence that braylin can represent a potential therapeutic use in preventing and treating cardiovascular diseases.

Potassium Channels as a Potential Target Spot for Drugs

Aberrant function or expression of potassium channels can be underlying in pathologies such as cardiac arrhythmia, diabetes mellitus, hypertension, preterm birth, and various types of cancer. The expression of potassium channels is altered in many types of diseases. Also, we have previously shown that natural polyphenols, such as resveratrol, and selective synthetic modulators of potassium channels, like pinacidil, can alter their function and lead to the desired outcome. Therefore, targeting potassium channels with substance, which has an influence on their function, is promising access to cancer, diabetes mellitus, preterm birth, or hypertension therapy. In this chapter, we could discuss strategies for targeting different types of potassium channels as potential targets for synthetic and natural molecules therapy.

Inhibition by Imipramine of the Voltage-Dependent K+ Channel in Rabbit Coronary Arterial Smooth Muscle Cells

Imipramine, a tricyclic antidepressant, is used in the treatment of depressive disorders. However, the effect of imipramine on vascular ion channels is unclear. Therefore, using a patch-clamp technique we examined the effect of imipramine on voltage-dependent K+ (Kv) channels in freshly isolated rabbit coronary arterial smooth muscle cells. Kv channels were inhibited by imipramine in a concentration-dependent manner, with an IC50 value of 5.55 ± 1.24 µM and a Hill coefficient of 0.73 ± 0.1. Application of imipramine shifted the steady-state activation curve in the positive direction, indicating that imipramine-induced inhibition of Kv channels was mediated by influencing the voltage sensors of the channels. The recovery time constants from Kv-channel inactivation were increased in the presence of imipramine. Furthermore, the application of train pulses (of 1 or 2 Hz) progressively augmented the imipramine-induced inhibition of Kv channels, suggesting that the inhibitory effect of imipramine is use (state) dependent. The magnitude of Kv current inhibition by imipramine was similar during the first, second, and third depolarizing pulses. These results indicate that imipramine-induced inhibition of Kv channels mainly occurs in the closed state. The imipramine-mediated inhibition of Kv channels was associated with the Kv1.5 channel, not the Kv2.1 or Kv7 channel. Inhibition of Kv channels by imipramine caused vasoconstriction. From these results, we conclude that imipramine inhibits vascular Kv channels in a concentration- and use (closed-state)-dependent manner by changing their gating properties regardless of its own function.

PKCζ-NADPH Oxidase-PKCα Dependent Kv1.5 Phosphorylation by Endothelin-1 Modulates Nav1.5-NCX1-Cav1.2 Axis in Stimulating Ca2+ Level in Caveolae of Pulmonary Artery Smooth Muscle Cells

Endothelin-1 (ET-1) is a potent endogenously derived vasoconstrictor, which increases pulmonary hypertension via stimulation of [Ca²⁺]_i level in pulmonary artery smooth muscle cells (PASMCs). In this communication, we sought to investigate the mechanism by which ET-1 causes stimulation of Ca²⁺ concentration in caveolae vesicles of bovine PASMCs (BPASMCs). ET-1 activates PKC-α in the caveolae vesicles by O₂^.- derived from PKCζ-NADPH oxidase dependent pathway. PKC-α phosphorylates Kv1.5 channels leading to a marked stimulation of Na⁺ and Ca²⁺ concentration in the caveolae vesicles. The stimulation of Ca²⁺ concentration in the caveolae vesicles by ET-1 occurs predominantly via Cav1.2 channels. Additionally, an increase in Na⁺ concentration by ET-1 due to stimulation of Nav1.5 channels marginally increases Ca²⁺ level in the caveolae vesicles via reverse-mode Na⁺/Ca²⁺ exchanger (NCX-1) and also through "slip-mode conductance" Nav1.5 channels. 4-AP, a well-known inhibitor of Kv channels, also increases Ca²⁺ concentration in the caveolae vesicles via Cav1.2 channels, reverse-mode NCX-1 and Nav1.5 channels by phosphorylation independent modulation of Kv1.5 channels without the involvement of PKCζ-NADPH oxidase-PKCα signaling axis. Overall, PKCζ-NADPH oxidase-PKCα dependent phosphorylation of Kv1.5 by ET-1 modulates Nav1.5-NCX1-Cav1.2 axis for stimulation of Ca²⁺ concentration in caveolae vesicles of BPASMCs, which provides a crucial mechanism for better understanding of ET-1-mediated modulation of pulmonary vascular tone.

Clinical Importance of the Human Umbilical Artery Potassium Channels

Potassium (K⁺) channels are usually predominant in the membranes of vascular smooth muscle cells (SMCs). These channels play an important role in regulating the membrane potential and vessel contractility-a role that depends on the vascular bed. Thus, the activity of K⁺ channels represents one of the main mechanisms regulating the vascular tone in physiological and pathophysiological conditions. Briefly, the activation of K⁺ channels in SMC leads to hyperpolarization and vasorelaxation, while its inhibition induces depolarization and consequent vascular contraction. Currently, there are four different types of K⁺ channels described in SMCs: voltage-dependent K⁺ (K_V) channels, calcium-activated K⁺ (K_Ca) channels, inward rectifier K⁺ (Kir) channels, and 2-pore domain K⁺ (K_2P) channels. Due to the fundamental role of K⁺ channels in excitable cells, these channels are promising therapeutic targets in clinical practice. Therefore, this review discusses the basic properties of the various types of K⁺ channels, including structure, cellular mechanisms that regulate their activity, and new advances in the development of activators and blockers of these channels. The vascular functions of these channels will be discussed with a focus on vascular SMCs of the human umbilical artery. Then, the clinical importance of K⁺ channels in the treatment and prevention of cardiovascular diseases during pregnancy, such as gestational hypertension and preeclampsia, will be explored.

Pregnancy-induced hypertension decreases Kv1.3 potassium channel expression and function in human umbilical vein smooth muscle

Voltage-gated potassium (K_v) channels are the largest superfamily of potassium (K) channels. A variety of K_v channels are expressed in the vascular smooth muscle cells (SMC). Studies have shown that gestational diabetes mellitus (GDM) and pregnancy-induced hypertension (PIH) cause various changes in the human umbilical vein (HUV). Recently, we have shown that 4-AP, a nonspecific K_v1-4 channel inhibitor, significantly decreases vasorelaxation induced by K channel opener pinacidil in vascular SMCs of the HUVs from normal pregnancies, but not in GDM and PIH. The goal of this study was to provide more detailed insight in the K_v channel subtypes involved in pinacidil-induced vasodilation of HUVs, as well as to investigate potential alterations of their function and expression during GDM and PIH. Margatoxin, a specific blocker of K_v1.2 and K_v1.3 channels, significantly antagonized pinacidil-induced vasorelaxation in normal pregnancy, while in HUVs from GDM and PIH that was not the case, indicating damage of K_v1.2 and K_v1.3 channel function. Immunohistochemistry and Western blot revealed similar expression of K_v1.2 channels in all groups. The expression of K_v1.3 subunit was significantly decreased in PIH, while it remained unchanged in GDM compared to normal pregnancy. Phrixotoxin, specific blocker of K_v4.2 and K_v4.3 channels, did not antagonize response to pinacidil in any of the groups. The major novel findings show that margatoxin antagonized pinacidil-induced relaxation in normal pregnancy, but not in GDM and PIH. Decreased expression of K_v1.3 channels in HUV during PIH may be important pathophysiological mechanism contributing to an increased risk of adverse pregnancy outcomes.

The vasodilatory effect of gemigliptin via activation of voltage-dependent K+ channels and SERCA pumps in aortic smooth muscle

This study investigated the vasodilatory effects and acting mechanism of gemigliptin, a dipeptidyl peptidase-4 (DPP-4) inhibitor. Tests were conducted in aortic rings pre-contracted with phenylephrine. Gemigliptin induced dose-dependent vasodilation of the aortic smooth muscle. Several pre-treatment groups were used to investigate the mechanism of action. While pre-treatment with paxilline, a large-conductance Ca²⁺-activated K⁺ channel inhibitor, glibenclamide, an ATP-sensitive K⁺ channel inhibitor, and Ba²⁺, an inwardly rectifying K⁺ channel inhibitor, had no impact on the vasodilatory effect of gemigliptin, pre-treatment with 4-aminopyridine, a voltage-dependent K⁺ (Kv) channel inhibitor, effectively attenuated the vasodilatory action of gemigliptin. In addition, pre-treatment with sarcoplasmic/endoplasmic reticulum Ca²⁺-ATPase (SERCA) pump inhibitors thapsigargin and cyclopiazonic acid significantly reduced the vasodilatory effect of gemigliptin. cAMP/PKA-related or cGMP/PKG-related signaling pathway inhibitors, including adenylyl cyclase inhibitor SQ 22536, PKA inhibitor KT 5720, guanylyl cyclase inhibitor ODQ, and PKG inhibitor KT 5823 did not alter the vasodilatory effect of gemigliptin. Similarly, elimination of the endothelium and pre-treatment with a nitric oxide (NO) synthase inhibitor (L-NAME) or small- and intermediate-conductance Ca²⁺-activated K⁺ channels (apamin and TRAM-34, respectively) did not change the gemigliptin effect. These findings suggested that gemigliptin induces vasodilation through the activation of Kv channels and SERCA pumps independent of cAMP/PKA-related or cGMP/PKG-related signaling pathways and the endothelium. Therefore, caution is required when prescribing gemigliptin to the patients with hypotension and diabetes.

Inhibition of voltage-dependent K+ channels by iloperidone in coronary arterial smooth muscle cells

Iloperidone, a second-generation atypical antipsychotic drug, is widely used in the treatment of schizophrenia. However, the side-effects of iloperidone on vascular K⁺ channels remain to be determined. Therefore, we explored the effect of iloperidone on voltage-dependent K⁺ (Kv) channels in rabbit coronary arterial smooth muscle cells using the whole-cell patch-clamp technique. Iloperidone inhibited vascular Kv channels in a concentration-dependent manner with a half-maximal inhibitory concentration (IC₅₀ ) of 2.11 ± 0.5 μM and a Hill coefficient of 0.68 ± 0.03. Iloperidone had no effect on the steady-state inactivation kinetics. However, it shifted the steady-state activation curve to the right, indicating that iloperidone inhibited Kv channels by influencing the voltage sensors. Application of 20 repetitive depolarizing pulses (1 and 2 Hz) progressively increased the inhibition of the Kv current in the presence of iloperidone. Furthermore, iloperidone increased the recovery time constant from Kv channel inactivation, suggesting that iloperidone-induced inhibition of Kv channels is use (state)-dependent. Pretreatment with a Kv1.5 inhibitor (diphenyl phosphine oxide 1 [DPO-1]) inhibited the Kv current to a level similar to that with iloperidone alone. However, pretreatment with a Kv2.1 or Kv7.X inhibitor (guangxitoxin or linopirdine) did not affect the inhibitory effect of iloperidone on Kv channels. Therefore, iloperidone directly inhibits Kv channels in a concentration- and use (state)-dependent manner independently of its antagonism of serotonin and dopamine receptors. Furthermore, the primary target of iloperidone is the Kv1.5 subtype.

Cardiorenal protection with SGLT2: Lessons from the cardiovascular outcome trials

Sodium glucose cotransporter 2 (SGLT2) inhibitors are a class of drugs that were primarily developed for the treatment of type 2 diabetes mellitus. However, these agents have shown to provide additional beneficial effects. We will discuss three main topics regarding the use of SGLT2 inhibitors: noncardiovascular effects, cardiovascular benefits, and novel clinical indications. Multiple clinical trials and preliminary studies across varying disciplines have shown that these agents exhibit cardiorenal-protective benefits, retinoprotective benefits, and may aid in weight loss without causing marked hypoglycemia. Therefore, these agents represent an avenue in clinical practice to manage comorbid conditions in the hyperglycemic patient. Because of their multifaceted effects and robust action, SGLT2 inhibitors represent therapy options for providers that not only provide beneficial clinical results but also reduce total patient drug burden.

Protriptyline, a tricyclic antidepressant, inhibits voltage-dependent K+ channels in rabbit coronary arterial smooth muscle cells

In this study, we explore the inhibitory effects of protriptyline, a tricyclic antidepressant drug, on voltage-dependent K+ (Kv) channels of rabbit coronary arterial smooth muscle cells using a whole-cell patch clamp technique. Protriptyline inhibited the vascular Kv current in a concentration-dependent manner, with an IC50 value of 5.05 ± 0.97 μM and a Hill coefficient of 0.73 ± 0.04. Protriptyline did not affect the steady-state activation kinetics. However, the drug shifted the steady-state inactivation curve to the left, suggesting that protriptyline inhibited the Kv channels by changing their voltage sensitivity. Application of 20 repetitive train pulses (1 or 2 Hz) progressively increased the protriptyline-induced inhibition of the Kv current, suggesting that protriptyline inhibited Kv channels in a use (state)-dependent manner. The extent of Kv current inhibition by protriptyline was similar during the first, second, and third step pulses. These results suggest that protriptyline-induced inhibition of the Kv current mainly occurs principally in the closed state. The increase in the inactivation recovery time constant in the presence of protriptyline also supported use (state)-dependent inhibition of Kv channels by the drug. In the presence of the Kv1.5 inhibitor, protriptyline did not induce further inhibition of the Kv channels. However, pretreatment with a Kv2.1 or Kv7 inhibitor induced further inhibition of Kv current to a similar extent to that observed with protriptyline alone. Thus, we conclude that protriptyline inhibits the vascular Kv channels in a concentration- and use-dependent manner by changing their gating properties. Furthermore, protriptyline-induced inhibition of Kv channels mainly involves the Kv1.5.

Vildagliptin, an Anti-diabetic Drug of the DPP-4 Inhibitor, Induces Vasodilation via Kv Channel and SERCA Pump Activation in Aortic Smooth Muscle

This study investigated vildagliptin-induced vasodilation and its related mechanisms using phenylephrine induced precontracted rabbit aortic rings. Vildagliptin induced vasodilation in a concentration-dependent manner. Pretreatment with the large-conductance Ca²⁺-activated K⁺ channel blocker paxilline, ATP-sensitive K⁺ channel blocker glibenclamide, and inwardly rectifying K⁺ channel blocker Ba²⁺ did not affect the vasodilatory effects of vildagliptin. However, application of the voltage-dependent K⁺ (Kv) channel inhibitor 4-aminopyridine significantly reduced the vasodilatory effects of vildagliptin. In addition, application of either of two sarcoplasmic/endoplasmic reticulum Ca²⁺-ATPase (SERCA) inhibitors, thapsigargin or cyclopiazonic acid, effectively inhibited the vasodilatory effects of vildagliptin. These vasodilatory effects were not affected by pretreatment with adenylyl cyclase, protein kinase A (PKA), guanylyl cyclase, or protein kinase G (PKG) inhibitors, or by removal of the endothelium. From these results, we concluded that vildagliptin induced vasodilation via activation of Kv channels and the SERCA pump. However, other K⁺ channels, PKA/PKG-related signaling cascades associated with vascular dilation, and the endothelium were not involved in vildagliptin-induced vasodilation.

Dipeptidyl peptidase-4 inhibitor sitagliptin induces vasorelaxation via the activation of Kv channels and PKA

The present study investigated the vasorelaxant effects of sitagliptin, which is a dipeptidyl peptidase-4 (DPP-4) inhibitor in aortic rings pre-contracted with phenylephrine (Phe). Sitagliptin induced vasorelaxation in a concentration-dependent manner but the inhibition of voltage-dependent K⁺ (Kv) channels by pretreatment with 4-aminopyridine (4-AP) effectively reduced this effect. By contrast, the inhibition of inward rectifier K⁺ (Kir) channels by pretreatment with barium (Ba²⁺), large-conductance calcium (Ca²⁺)-activated K⁺ (BK_Ca) channels with paxilline, and adenosine triphosphate (ATP)-sensitive K⁺ (K_ATP) channels with glibenclamide did not change this effect. Although the application of SQ 22536, which is an adenylyl cyclase inhibitor, also did not change this effect, treatment with KT 5720, a protein kinase A (PKA) inhibitor, effectively reduced the vasorelaxant effects of sitagliptin. ODQ, which is a guanylyl cyclase inhibitor, and KT 5823, a protein kinase G (PKG) inhibitor, did not impact the effect. Furthermore, neither the inhibition of Ca²⁺ channels by pretreatment with nifedipine nor the inhibition of sarcoplasmic/endoplasmic reticulum Ca²⁺-ATPase (SERCA) pumps by pretreatment with thapsigargin changed the effect. Similarly, the effects of sitagliptin were not altered by eliminating the endothelium, by pretreatment with a nitric oxide (NO) synthase inhibitor (L-NAME), or by inhibition of small- and intermediate-conductance Ca²⁺-activated K⁺ channels (SK_Ca and IK_Ca) using apamin and TRAM-34. Taken together, these results suggest that sitagliptin induces vasorelaxation by inhibiting both membrane potential (Em)-dependent and -independent vasoconstriction and activating PKA and Kv channels independently of PKG signaling pathways, other K⁺ channels, SERCA pumps, and the endothelium.

Hypoxic pulmonary vasoconstriction is lacking in rats with type 1 diabetes

Hypoxic pulmonary vasoconstriction (HPV) is the most important feature of intact lung circulation that matches local blood perfusion to ventilation. The main goal of this work was to study the effects of diabetes on the development of HPV in rats. The experimental design comprised diabetes mellitus induction by streptozotocin, video-morphometric measurements of the lumen area of intrapulmonary arteries (iPAs) using perfused lung tissue slices and patch-clamp techniques. It was shown that iPA lumen size was significantly reduced under physical and chemical hypoxia (7-10 mm Hg) in normal iPA, but, on the contrary, it clearly increased in diabetic lung slices. The amplitude of the outward K⁺ current in diabetic iPAs smooth muscle cells (SMCs) was two-fold greater than that seen in healthy cells. Chemical hypoxia led to significant decrease in the amplitude of the K⁺ outward current in healthy iPA SMCs while it was without effect in diabetic cells. The data obtained clearly indicate a significant dysregulation of vascular tone in pulmonary circulation under diabetes, ie diabetes damages the adaptive mechanism for regulating blood flow from poorly ventilated to better ventilated regions of the lung under hypoxia. This effect could be clinically important for patients with diabetes who have acute or chronic lung diseases associated with the lack of blood oxygenation.

Potassium channels in vascular smooth muscle: a pathophysiological and pharmacological perspective

Potassium (K⁺ ) ion channel activity is an important determinant of vascular tone by regulating cell membrane potential (MP). Activation of K⁺ channels leads to membrane hyperpolarization and subsequently vasodilatation, while inhibition of the channels causes membrane depolarization and then vasoconstriction. So far five distinct types of K⁺ channels have been identified in vascular smooth muscle cells (VSMCs): Ca⁺² -activated K⁺ channels (BK_{C a} ), voltage-dependent K⁺ channels (K_V ), ATP-sensitive K⁺ channels (K_ATP ), inward rectifier K⁺ channels (K_ir ), and tandem two-pore K⁺ channels (K₂ P). The activity and expression of vascular K⁺ channels are changed during major vascular diseases such as hypertension, pulmonary hypertension, hypercholesterolemia, atherosclerosis, and diabetes mellitus. The defective function of K⁺ channels is commonly associated with impaired vascular responses and is likely to become as a result of changes in K⁺ channels during vascular diseases. Increased K⁺ channel function and expression may also help to compensate for increased abnormal vascular tone. There are many pharmacological and genotypic studies which were carried out on the subtypes of K⁺ channels expressed in variable amounts in different vascular beds. Modulation of K⁺ channel activity by molecular approaches and selective drug development may be a novel treatment modality for vascular dysfunction in the future. This review presents the basic properties, physiological functions, pathophysiological, and pharmacological roles of the five major classes of K⁺ channels that have been determined in VSMCs.

Shaker-related voltage-gated K+ channel expression and vasomotor function in human coronary resistance arteries

OBJECTIVES

K_V channels are important regulators of vascular tone, but the identity of specific K_V channels involved and their regulation in disease remain less well understood. We determined the expression of K_V 1 channel subunits and their role in cAMP-mediated dilation in coronary resistance arteries from subjects with and without CAD.

METHODS

HCAs from patients with and without CAD were assessed for mRNA and protein expression of K_V 1 channel subunits with molecular techniques and for vasodilator response with isolated arterial myography.

RESULTS

Assays of mRNA transcripts, membrane protein expression, and vascular cell-specific localization revealed abundant expression of K_V 1.5 in vascular smooth muscle cells of non-CAD HCAs. Isoproterenol and forskolin, two distinct cAMP-mediated vasodilators, induced potent dilation of non-CAD arterioles, which was inhibited by both the general K_V blocker 4-AP and the selective K_V 1.5 blocker DPO-1. The cAMP-mediated dilation was reduced in CAD and was accompanied by a loss of or reduced contribution of 4-AP-sensitive K_V channels.

CONCLUSIONS

K_V 1.5, as a major 4-AP-sensitive K_V 1 channel expressed in coronary VSMCs, mediates cAMP-mediated dilation in non-CAD arterioles. The cAMP-mediated dilation is reduced in CAD coronary arterioles, which is associated with impaired 4-AP-sensitive K_V channel function.

KV channels and the regulation of vascular smooth muscle tone

VSMCs in resistance arteries and arterioles express a diverse array of K_V channels with members of the K_V 1, K_V 2 and K_V 7 families being particularly important. Members of the K_V channel family: (i) are highly expressed in VSMCs; (ii) are active at the resting membrane potential of VSMCs in vivo (-45 to -30 mV); (iii) contribute to the negative feedback regulation of VSMC membrane potential and myogenic tone; (iv) are activated by cAMP-related vasodilators, hydrogen sulfide and hydrogen peroxide; (v) are inhibited by increases in intracellular Ca²⁺ and vasoconstrictors that signal through G_q -coupled receptors; (vi) are involved in the proliferative phenotype of VSMCs; and (vii) are modulated by diseases such as hypertension, obesity, the metabolic syndrome and diabetes. Thus, K_V channels participate in every aspect of the regulation of VSMC function in both health and disease.

The Kv7 channel activator, retigabine, induces vasorelaxation via an endothelial-independent pathway in male mouse aorta

PURPOSE

Previous studies have indicated that Kv7 channels have an important role in the regulation of blood vessel reactivity, including in the coronary, renal, and cerebral arteries. The present studies examined whether Kv7 channels regulated vascular reactivity in the mouse aorta and investigated the mechanisms involved in the reactivity.

METHODS

Wild-type (WT) male C57BL/6 mice, between 10 and 15 weeks old, were used in this study. The vascular function of the aorta in WT male mice was assessed by using a pin myography system (Model 620; DMT, Denmark).

RESULTS

Vasorelaxation by an endothelial-dependent vasodilator, acetylcholine (ACh, 1 nM - 10 μM) and an endothelial-independent vasodilator, sodium nitroprusside (SNP, 1 nM - 10 μM) was induced in the aorta in a dose-dependent manner. Pre-incubation with the nitric oxide synthase inhibitor, L-NAME (100 μM, 20 min), completely abolished ACh-induced vasorelaxation, but did not block retigabine-induced vasorelaxation, which suggested that retigabine caused vasorelaxation in the aorta via smooth muscle activation rather than via endothelial cells. Pre-application of the Kv7 channel blocker, linopirdine (10 μM), resulted in a greater contractile response compared with that induced by vehicle in the aorta. In addition, pre-incubation with linopirdine (10 μM, 20 min) reduced retigabine-induced vasorelaxation (1-50 μM).

CONCLUSION

This study has provided evidence that Kv7 channels may play a role in the regulation of aortic blood flow via smooth muscle activation.

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.

Blockade of voltage-dependent K+ current in rabbit coronary arterial smooth muscle cells by the tricyclic antidepressant clomipramine

We investigated the effect of the tricyclic antidepressant clomipramine on voltage-dependent K⁺ (Kv) channels in native rabbit coronary arterial smooth muscle cells. Our results showed that clomipramine inhibited vascular Kv channels in a concentration-dependent manner, with an IC₅₀ value of 8.61 ± 4.86 μM and a Hill coefficient (n) of 0.58 ± 0.07. The application of 10 μM clomipramine did not affect the activation curves of the Kv channels; however, the inactivation curves of the Kv channels were shifted toward a more negative potential. The clomipramine-induced inhibition of Kv currents was not changed by the application of train pulses (1 or 2 Hz), which demonstrated that clomipramine inhibited Kv current in a state (use)-independent manner. Pretreatment with the Kv1.5 and Kv2.1 inhibitors, DPO-1 and guangxitoxin, respectively, partially reduced the clomipramine-induced inhibition of Kv currents. Therefore, we concluded that clomipramine inhibited vascular Kv channels in a concentration-dependent, but state (use)-independent manner, regardless of its own function.

Salvia miltiorrhiza: A Potential Red Light to the Development of Cardiovascular Diseases

Salvia miltiorrhiza Bunge, also known as Danshen in Chinese, has been widely used to treat cardiovascular diseases (CVD) in China and other Asia countries. Here, we summarize literatures of the historical traditional Chinese medicine (TCM) interpretation of the action of Salvia miltiorrhiza, its use in current clinical trials, its main phytochemical constituents and its pharmacological findings by consulting Pubmed, China Knowledge Resource Integrated, China Science and Technology Journal, and the Web of Science Databases. Since 2000, 39 clinical trials have been identified that used S. miltiorrhiza in TCM prescriptions alone or with other herbs for the treatment of patients with CVD. More than 200 individual compounds have been isolated and characterized from S. miltiorrhiza, which exhibited various pharmacological activities targeting different pathways for the treatment of CVD in various animal and cell models. The isolated compounds may provide new perspectives in alternative treatment regimes and reveal novel chemical scaffolds for the development of anti-CVD drugs. Meanwhile, there are also some rising concerns of the potential side effects and drug-drug interactions of this plant. The insights gained from this study will help us to better understanding of the actions of this herb for management of cardiovascular disorders. As an herb of red root, S. miltiorrhiza will act as a potential red light to prevent the development of CVD.

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 BK_Ca channel inhibitor paxilline, the K_ATP 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.

Role of renal vascular potassium channels in physiology and pathophysiology

The control of renal vascular tone is important for the regulation of salt and water balance, blood pressure and the protection against damaging elevated glomerular pressure. The K⁺ conductance is a major factor in the regulation of the membrane potential (V_m ) in vascular smooth muscle (VSMC) and endothelial cells (EC). The vascular tone is controlled by V_m via its effect on the opening probability of voltage-operated Ca²⁺ channels (VOCC) in VSMC. When K⁺ conductance increases V_m becomes more negative and vasodilation follows, while deactivation of K⁺ channels leads to depolarization and vasoconstriction. K⁺ channels in EC indirectly participate in the control of vascular tone by endothelium-derived vasodilation. Therefore, by regulating the tone of renal resistance vessels, K⁺ channels have a potential role in the control of fluid homoeostasis and blood pressure as well as in the protection of the renal parenchyma. The main classes of K⁺ channels (calcium activated (K_Ca ), inward rectifier (K_ir ), voltage activated (K_v ) and ATP sensitive (K_ATP )) have been found in the renal vessels. In this review, we summarize results available in the literature and our own studies in the field. We compare the ambiguous in vitro and in vivo results. We discuss the role of single types of K⁺ channels and the integrated function of several classes. We also deal with the possible role of renal vascular K⁺ channels in the pathophysiology of hypertension, diabetes mellitus and sepsis.

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⁺ (BK_Ca) channel blocker paxilline, inwardly rectifying K⁺ (Kir) channel blocker Ba²⁺, and ATP-sensitive K⁺ (K_ATP) 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 vasorelaxant effect of antidiabetic 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⁺ (BK_Ca ) channel inhibitor paxilline, the inwardly rectifying K⁺ (Kir) channel inhibitor Ba²⁺ , and ATP-sensitive K⁺ (K_ATP ) 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⁺ (SK_Ca ) 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.

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

We examined the effects of the PPARα 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 ± 0.53μM 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± 0.05μM^-1s^-1 and 4.70 ± 0.47s^-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 2Hz) 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 PPARα activator, bezafibrate and PPARα 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 PPARα activation.

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.

Neuronal Voltage Gated Potassium Channels May Modulate Nitric Oxide Synthesis in Corpus Cavernosum

Potassium channels (K⁺Ch) in corpus cavernosum play an important role in the regulation of erection. Nitric oxide (NO) acts through opening of K⁺Ch leading to hyperpolarization and relaxation.

Aim : This study aims to update knowledge about the role of voltage-gated K⁺Ch (K_V) channels in erectile machinery and investigate their role in the control of NO action &/or synthesis in the corpus cavernosum.

Methods : Tension studies using isolated rabbit corpus cavernosum (CC) strips and rat anococcygeus muscle were conducted. Results are expressed as mean ± SEM.

Results : Electric field stimulation (EFS, 2–16 Hz) evoked frequency-dependent relaxations of the PE (phenylephrine)-precontracted CC strips. At 2 Hz, EFS-induced relaxation amounted to 73.17 ± 2.55% in presence 4-AP (10⁻³ M) compared to 41.98 ± 1.45% as control. None of the other selective K⁺Ch blockers tested inhibited EFS-induced relaxation. 4-AP (10⁻³M) significantly attenuated ACh-induced relaxation of rabbit CC where dose-response curve was clearly shifted upward, and attenuated SNP- induced relaxation, for example, to 49.28 ± 4.52% compared to 65.53 ± 3.01% as control at 10⁻⁶ M SNP. The potentiatory effect of 4-AP on EFS was abolished or reversed in presence of N^G-nitro-L-arginine (L-NNA, non-selective nitric oxide synthase inhibitor, 10⁻⁵M, and 2 × 10⁻⁴M). Same results were observed in rat anococcygeus muscle which is a part of the erectile machinery in rats.

Conclusion : This study provides evidence for the presence of prejunctional voltage-gated K⁺Ch in CC, the blockade of which may increase the neuronal synthesis of NO.

Smooth Muscle Ion Channels and Regulation of Vascular Tone in Resistance Arteries and Arterioles

Vascular tone of resistance arteries and arterioles determines peripheral vascular resistance, contributing to the regulation of blood pressure and blood flow to, and within the body's tissues and organs. Ion channels in the plasma membrane and endoplasmic reticulum of vascular smooth muscle cells (SMCs) in these blood vessels importantly contribute to the regulation of intracellular Ca2+ concentration, the primary determinant of SMC contractile activity and vascular tone. Ion channels provide the main source of activator Ca2+ that determines vascular tone, and strongly contribute to setting and regulating membrane potential, which, in turn, regulates the open-state-probability of voltage gated Ca2+ channels (VGCCs), the primary source of Ca2+ in resistance artery and arteriolar SMCs. Ion channel function is also modulated by vasoconstrictors and vasodilators, contributing to all aspects of the regulation of vascular tone. This review will focus on the physiology of VGCCs, voltage-gated K+ (KV) channels, large-conductance Ca2+-activated K+ (BKCa) channels, strong-inward-rectifier K+ (KIR) channels, ATP-sensitive K+ (KATP) channels, ryanodine receptors (RyRs), inositol 1,4,5-trisphosphate receptors (IP3Rs), and a variety of transient receptor potential (TRP) channels that contribute to pressure-induced myogenic tone in resistance arteries and arterioles, the modulation of the function of these ion channels by vasoconstrictors and vasodilators, their role in the functional regulation of tissue blood flow and their dysfunction in diseases such as hypertension, obesity, and diabetes. © 2017 American Physiological Society. Compr Physiol 7:485-581, 2017.

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 mu M and a slope value (Hill coefficient) of 0.61. Although the application of 1 mu M 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.

Nortriptyline, a tricyclic antidepressant, inhibits voltage-dependent K+ channels in coronary arterial smooth muscle cells

We demonstrated the effect of nortriptyline, a tricyclic antidepressant drug and serotonin reuptake inhibitor, on voltage-dependent K⁺ (Kv) channels in freshly isolated rabbit coronary arterial smooth muscle cells using a whole-cell patch clamp technique. Nortriptyline inhibited Kv currents in a concentration-dependent manner, with an apparent IC₅₀ value of 2.86±0.52 µM and a Hill coefficient of 0.77±0.1. Although application of nortriptyline did not change the activation curve, nortriptyline shifted the inactivation current toward a more negative potential. Application of train pulses (1 or 2 Hz) did not change the nortriptyline-induced Kv channel inhibition, suggesting that the effects of nortiprtyline were not use-dependent. Preincubation with the Kv1.5 and Kv2.1/2.2 inhibitors, DPO-1 and guangxitoxin did not affect nortriptyline inhibition of Kv channels. From these results, we concluded that nortriptyline inhibited Kv channels in a concentration-dependent and state-independent manner independently of serotonin reuptake.

Comparison of Voltage Gated K+ Currents in Arterial Myocytes with Heterologously Expressed K v Subunits

We have shown that three components contribute to functional voltage gated K⁺ (K _v) currents in rat small mesenteric artery myocytes: (1) Kv1.2 plus Kv1.5 with Kvβ1.2 subunits, (2) Kv2.1 probably associated with Kv9.3 subunits, and (3) Kv7.4 subunits. To confirm and address subunit stoichiometry of the first two, we have compared the biophysical properties of K _v currents in small mesenteric artery myocytes with those of K_v subunits heterologously expressed in HEK293 cells using whole cell voltage clamp methods. Selective inhibitors of Kv1 (correolide, COR) and Kv2 (stromatoxin, ScTx) channels were used to separate these K _v current components. Conductance-voltage and steady state inactivation data along with time constants of activation, inactivation, and deactivation of native K _v components were generally well represented by those of Kv1.2-1.5-β1.2 and Kv2.1-9.3 channels. The slope of the steady state inactivation-voltage curve (availability slope) proved to be the most sensitive measure of accessory subunit presence. The availability slope curves exhibited a single peak for both native K _v components. Availability slope curves for Kv1.2-1.5-β1.2 and Kv2.1-9.3 channels expressed in human embryonic kidney cells also exhibited a single peak that shifted to more depolarized voltages with increasing accessory to α subunit transfection ratio. Availability slope curves for SxTc-insensitive currents were similar to those of Kv1.2-1.5 expressed with Kvβ1.2 at a 1:5 molar ratio while curves for COR-insensitive currents closely resembled those of Kv2.1 expressed with Kv9.3 at a 1:1 molar ratio. These results support the suggested K_v subunit combinations in small mesenteric artery, and further suggest that Kv1 α and Kvβ1.2 but not Kv2.1 and Kv9.3 subunits are present in a saturated (4:4) stoichiometry.

Cisapride, a selective serotonin 5-HT4-receptor agonist, inhibits voltage-dependent K(+) channels in rabbit coronary arterial smooth muscle cells

We investigated the effect of cisapride, a selective serotonin 5-HT4-receptor agonist, on voltage-dependent K(+) (Kv) channels using freshly isolated smooth muscle cells from the coronary arteries of rabbits. The amplitude of Kv currents was reduced by cisapride in a concentration-dependent manner, with an IC50 value of 6.77 ± 6.01 μM and a Hill coefficient of 0.51 ± 0.18. The application of cisapride shifted the steady-state inactivation curve toward a more negative potential, but had no significant effect on the steady-state activation curve. This suggested that cisapride inhibited the Kv channel in a closed state by changing the voltage sensitivity of Kv channels. The application of another selective serotonin 5-HT4-receptor agonist, prucalopride, did not affect the basal Kv current and did not alter the inhibitory effect of cisapride on Kv channels. From these results, we concluded that cisapride inhibited vascular Kv current in a concentration-dependent manner by shifting the steady-state inactivation curve, independent of its own function as a selective serotonin 5-HT4-receptor agonist.