K+ channel modulation in arterial smooth muscle

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.

Oxidative and Nitrous Stress Underlies Vascular Malfunction Induced by Ionizing Radiation and Diabetes

Oxidative stress results from the production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in quantities exceeding the potential activity of the body's antioxidant system and is one of the risk factors for the development of vascular dysfunction in diabetes and exposure to ionizing radiation. Being the secondary products of normal aerobic metabolism in living organisms, ROS and RNS act as signaling molecules that play an important role in the regulation of vital organism functions. Meanwhile, in high concentrations, these compounds are toxic and disrupt various metabolic pathways. The various stress factors (hyperglycemia, gamma-irradiation, etc.) trigger free oxygen and nitrogen radicals accumulation in cells that are capable to damage almost all cellular components including ion channels and transporters such as Na+/K+-ATPase, BKCa, and TRP channels. Vascular dysfunctions are governed by interaction of ROS and RNS. For example, the reaction of ROS with NO produces peroxynitrite (ONOO-), which not only oxidizes DNA, cellular proteins, and lipids, but also disrupts important signaling pathways that regulate the cation channel functions in the vascular endothelium. Further increasing in ROS levels and formation of ONOO- leads to reduced NO bioavailability and causes endothelial dysfunction. Thus, imbalance of ROS and RNS and their affect on membrane ion channels plays an important role in the pathogenesis of vascular dysfunction associated with various disorders.

Bibliometric analysis of research progress on tetramethylpyrazine and its effects on ischemia-reperfusion injury

In recent decades, natural products have attracted worldwide attention and become one of the most important resources for pharmacological industries and medical sciences to identify novel drug candidates for disease treatment. Tetramethylpyrazine (TMP) is an alkaloid extracted from Ligusticum chuanxiong Hort., which has shown great therapeutic potential in cardiovascular and cerebrovascular diseases, liver and renal injury, as well as cancer. In this review, we analyzed 1270 papers published on the Web of Science Core Collection from 2002 to 2022 and found that TMP exerted significant protective effects on ischemia-reperfusion (I/R) injury that is the cause of pathological damages in a variety of conditions, such as ischemic stroke, myocardial infarction, acute kidney injury, and liver transplantation. TMP is limited in clinical applications to some extent due to its rapid metabolism, a short biological half-life and poor bioavailability. Obviously, the structural modification, administration methods and dosage forms of TMP need to be further investigated in order to improve its bioavailability. This review summarizes the clinical applications of TMP, elucidates its potential mechanisms in protecting I/R injury, provides strategies to improve bioavailability, which presents a comprehensive understanding of the important compound. Hopefully, the information and knowledge from this review can help researchers and physicians to better improve the applications of TMP in the clinic.

Dilation of porcine retinal arterioles to nobiletin, a polymethoxyflavonoid: Roles of nitric oxide and voltage-dependent potassium channel

We examined the effects of nobiletin, a polymethoxyflavonoid, on the retinal microvascular diameter to determine if they depend on the endothelium and/or smooth muscle to reveal the signaling mechanisms involved in this vasomotor activity. Porcine retinal arterioles were isolated, cannulated, and pressurized without flow in vitro. Video microscopic techniques recorded diametric responses to nobiletin. The retinal arterioles dilated in a nobiletin concentration-dependent (100 pM-10 μM) manner and decreased by 50% after endothelial removal. The nitric oxide (NO) synthase inhibitor, Nω-nitro-L-arginine methyl ester (L-NAME), reduced nobiletin-induced vasodilation comparable to denudation. Blockade of soluble guanylyl cyclase by 1H-[1,2,4] oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ) produced a similar inhibitory effect as that by L-NAME. Nobiletin-induced vasodilation was also inhibited by the nonselective potassium channel inhibitor, tetraethylammonium (TEA), and the voltage-gated K (Kv) inhibitor, 4-aminopyridine. Co-administration of L-NAME and TEA almost eliminated nobiletin-induced vasodilation. Nobiletin elicits both endothelium-dependent and -independent dilation of retinal arterioles mediated by NO release and Kv channel activation, respectively.

Evaluation of vasodilatory effect and antihypertensive effect of chrysin through in vitro and sub-chronic in vivo study

Chrysin, a bioflavonoid belonging to the flavone, occurs naturally in plants such as the passionflower, honey and propolis. Few studies have demonstrated that chrysin can promote vasorelaxant activities in rats' aorta and mesenteric arteries. To date, no research has explored the signalling system routes that chrysin may utilise to produce its vasorelaxant action. Therefore, this study aimed to investigate the underlying mechanisms involved in chrysin-induced vasorelaxant in rats' aortic rings and assess the antihypertensive effect of chrysin in spontaneously hypertensive rats (SHRs). The findings revealed that chrysin utilised both endothelium-dependent and endothelium-independent mechanisms. The presence of L-NAME (endothelial NO synthase inhibitor), ODQ (sGC inhibitor), methylene blue (cGMP lowering agent), 4-AP (voltage-gated potassium channel inhibitor), atropine (muscarinic receptors inhibitor) and propranolol (β-adrenergic receptors inhibitor) significantly reduced the chrysin's vasorelaxant action. Furthermore, chrysin can reduce intracellular Ca²⁺ levels by limiting the extracellular intake of Ca²⁺ through voltage-operated calcium channels and blocking the intracellular release of Ca²⁺ from the sarcoplasmic reticulum via the IP₃ receptor. These indicate that chrysin-induced vasorelaxants involved NO/sGC/cGMP signalling cascade, muscarinic and β-adrenergic receptors, also the potassium and calcium channels. Although chrysin had vasorelaxant effects in in vitro studies, the in vivo antihypertensive experiment discovered chrysin does not significantly reduce the blood pressure of SHRs following 21 days of oral treatment. This study proved that chrysin utilised multiple signalling pathways to produce its vasorelaxant effect in the thoracic aorta of rats; however, it had no antihypertensive effect on SHRs.

Aging-induced down-regulation of Pka/Bkca pathway in rat cerebral arteries

The incidence of cerebrovascular diseases increases significantly with aging. This study aimed to test the hypothesis that aging may influence the protein kinase A (PKA)-dependent vasodilation via RyR/BKCa pathway in the middle cerebral arteries (MCA). Male Sprague-Dawley rats were randomly divided into control (4-6 month-old) and aged (24-month-old) groups. The functions of MCA and ion channel activities in smooth muscle cells were examined using myograph system and patch-clamp. Aging decreased the isoproterenol/forskolin-induced relaxation in the MCA. Large-conductance Ca2+-activated-K+ (BKCa) channel inhibitor, iberiotoxin, significantly attenuated the forskolin-induced vasodilatation and hyperpolarization in the young group, but not in the aged group. The amplitude and frequency of spontaneous transient outward currents (STOCs) were significantly decreased in the aged group. Single channel recording revealed that the mean open time of BKCa channels were decreased, while an increased mean closed time of BKCa channels were found in the aged group. The Ca2+/voltage sensitivity of the channels was decreased accompanied by reduced BKCa α and β1-subunit, the expression of RyR2, PKA-Cα and PKA-Cβ subunits were also declined in the aged group. Aging induced down-regulation of PKA/BKCa pathway in cerebral artery in rats. The results provides new information on further understanding in cerebrovascular diseases resulted from age-related cerebral vascular dysfunction.

Physiological features of cells and microvasculature under the local hypothermia influence

Hypothermia or cold therapy is the local or systemic application of cold for therapeutic purposes. Local application of cold is used to control inflammation: pain and swelling, hematoma and trismus reduction. Despite the frequent use of cooling in prosthodontic rehabilitation and in physical therapy, as evidenced by many reports in the literature, there is scientific documentation that suggests disadvantages of using this treatment in maxillofacial surgery and oral surgery. Also the clinical studies that have been carried out in maxillofacial surgery and oral surgery have been conducted in an empirical manner, which casts doubt on the results. In view of this, it is relevant to study the mechanisms of microcirculatory preconditioning and hypothermia. This physiological process is so interesting for the development of medical devices of controlled hardware hypothermia to prevent inflammatory symptoms at the stage of rehabilitation by targeting the vascular and cellular component of the inflammatory process in different areas of the human body. To date, the use of local hardware controlled hypothermia in various pathological conditions in humans is a topical trend in medicine. Microcirculatory bloodstream is directly related to temperature factors. Although there are concepts of vascular spasm or dilatation in the microcirculatory bloodstream during systemic hypothermia, there are no reliable data on the cellular and vascular reactions during local hypothermia. In this paper, a search for fundamental and current scientific work on the topic of cellular and vascular changes under the influence of hypothermia was conducted. The search for data revealed that the mechanisms of intracellular hypothermia are of particular interest for the development of therapeutic treatments after surgical interventions in areas with extensive blood supply. With this in mind, it is relevant to investigate several areas: the role of endothelium, glycocalyx and blood cells in microcirculatory-mediated preconditioning and intracellular hypothermia, and in the molecular mechanism that regulates these processes, whether they occur in the same way in all tissues.

Physiological features of cells and microvasculature under the local hypothermia influence

Hypothermia or cold therapy is the local or systemic application of cold for therapeutic purposes. Local application of cold is used to control inflammation: pain and swelling, hematoma and trismus reduction. Despite the frequent use of cooling in prosthodontic rehabilitation and in physical therapy, as evidenced by many reports in the literature, there is scientific documentation that suggests disadvantages of using this treatment in maxillofacial surgery and oral surgery. Also the clinical studies that have been carried out in maxillofacial surgery and oral surgery have been conducted in an empirical manner, which casts doubt on the results. In view of this, it is relevant to study the mechanisms of microcirculatory preconditioning and hypothermia. This physiological process is so interesting for the development of medical devices of controlled hardware hypothermia to prevent inflammatory symptoms at the stage of rehabilitation by targeting the vascular and cellular component of the inflammatory process in different areas of the human body. To date, the use of local hardware controlled hypothermia in various pathological conditions in humans is a topical trend in medicine. Microcirculatory bloodstream is directly related to temperature factors. Although there are concepts of vascular spasm or dilatation in the microcirculatory bloodstream during systemic hypothermia, there are no reliable data on the cellular and vascular reactions during local hypothermia. In this paper, a search for fundamental and current scientific work on the topic of cellular and vascular changes under the influence of hypothermia was conducted. The search for data revealed that the mechanisms of intracellular hypothermia are of particular interest for the development of therapeutic treatments after surgical interventions in areas with extensive blood supply. With this in mind, it is relevant to investigate several areas: the role of endothelium, glycocalyx and blood cells in microcirculatory-mediated preconditioning and intracellular hypothermia, and in the molecular mechanism that regulates these processes, whether they occur in the same way in all tissues.

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.

Ethyl Acetate Fraction from Leandra dasytricha (A. Gray) Cong. Leaves Promotes Vasodilatation and Reduces Blood Pressure in Normotensive and Hypertensive Rats

Leandra dasytricha (A. Gray) Cong. is widely distributed in the south of Brazil and is commonly used for cardiovascular and kidney ailments. For this study, we used male Wistar normotensive rats (NTRs) and spontaneously hypertensive rats (SHRs) to verify the effects of the ethyl acetate fraction (EAF) obtained from L. dasytricha leaves on isolated aorta relaxation and in the arterial blood pressure. The EAF was analyzed by LC-DAD-MS, and several components were annotated, including hydrolysable tannins, triterpenes, and O- and C-glycosylated dihydrochalcones, such as the most intense ion peak relative to C-hexosyl phloretin (nothofagin; compound number 13). The EAF caused a concentration and endothelium-dependent relaxation of the aorta in both NTRs and SHRs. This effect was abolished in the endothelium-denuded aorta. L-NAME, a nonselective nitric oxide synthase inhibitor, and ODQ, a soluble guanylate cyclase inhibitor, entirely blocked the EAF-induced relaxation. The presence of a muscarinic receptor antagonist or a cyclooxygenase inhibitor did not alter the EAF's effectiveness in relaxing the aorta. The preincubation with tetraethylammonium, a Ca²⁺-activated K⁺ channel blocker, and with 4-aminopyridine, a voltage-dependent K⁺ channel blocker, significantly interfered with the EAF's relaxation. However, the incubation with glibenclamide, an ATP-sensitive K⁺ channel blocker, and barium chloride, an inward-rectifier K⁺ channel blocker, did not interfere with the EAF-induced relaxation. The EAF treatment also caused a dose-dependent decrease in the mean arterial pressure, systolic arterial pressure, and diastolic arterial pressure of both NTRs and SHRs, without significantly interfering with heart rate values. In conclusion, this study demonstrated the EAF-induced vasorelaxant and hypotensive actions, primarily dependent on the endothelium function and mainly with the participation of the nitric oxide and Ca²⁺-activated and voltage-dependent K⁺ channels.

Alzheimer's disease and cerebrovascular pathology alter brain endothelial inward rectifier potassium (KIR 2.1) channels

Background and Purpose

Inward rectifier potassium (K_IR) channels are key effectors of vasodilatation in neurovascular coupling (NVC). K_IR channels expressed in cerebral endothelial cells (ECs) have been confirmed as essential modulators of NVC. Alzheimer's disease (AD) and cerebrovascular disease (CVD) impact on EC‐K_IR channel function, but whether oxidative stress or inflammation explains this impairment remains elusive.

Experimental Approach

We evaluated K_IR channel function in intact and EC‐denuded pial arteries of wild‐type (WT) and transgenic mice overexpressing a mutated form of the human amyloid precursor protein (APP mice, recapitulating amyloid β‐induced oxidative stress seen in AD) or a constitutively active form of TGF‐β1 (TGF mice, recapitulating inflammation seen in cerebrovascular pathology). The benefits of antioxidant (catalase) or anti‐inflammatory (indomethacin) drugs also were investigated. Vascular and neuronal components of NVC were assessed in vivo.

Key Results

Our findings show that (i) K_IR channel‐mediated maximal vasodilatation in APP and TGF mice reaches only 37% and 10%, respectively, of the response seen in WT mice; (ii) K_IR channel dysfunction results from K_IR2.1 subunit impairment; (iii) about 50% of K⁺‐induced artery dilatation is mediated by EC‐K_IR channels; (iv) oxidative stress and inflammation impair K_IR channel function, which can be restored by antioxidant and anti‐inflammatory drugs; and (v) inflammation induces K_IR2.1 overexpression and impairs NVC in TGF mice.

Conclusion and Implications

Therapies targeting both oxidative stress and inflammation are necessary for full recovery of K_IR2.1 channel function in cerebrovascular pathology caused by AD and CVD.

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.

Hypoxia and metabolic inhibitors alter the intracellular ATP:ADP ratio and membrane potential in human coronary artery smooth muscle cells

ATP-sensitive potassium (KATP) channels couple cellular metabolism to excitability, making them ideal candidate sensors for hypoxic vasodilation. However, it is still unknown whether cellular nucleotide levels are affected sufficiently to activate vascular KATP channels during hypoxia. To address this fundamental issue, we measured changes in the intracellular ATP:ADP ratio using the biosensors Perceval/PercevalHR, and membrane potential using the fluorescent probe DiBAC4(3) in human coronary artery smooth muscle cells (HCASMCs). ATP:ADP ratio was significantly reduced by exposure to hypoxia. Application of metabolic inhibitors for oxidative phosphorylation also reduced ATP:ADP ratio. Hyperpolarization caused by inhibiting oxidative phosphorylation was blocked by either 10 µM glibenclamide or 60 mM K+. Hyperpolarization caused by hypoxia was abolished by 60 mM K+ but not by individual K+ channel inhibitors. Taken together, these results suggest hypoxia causes hyperpolarization in part by modulating K+ channels in SMCs.

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.

4-Aminopyridine, a Voltage-Gated K+ Channel Inhibitor, Attenuates Nitric Oxide-Mediated Vasodilation of Retinal Arterioles in Rats

Nitric oxide (NO) is an important regulator of the retinal blood flow. The present study aimed to determine the role of voltage-gated K⁺ (K_V) channels and ATP-sensitive K⁺ (K_ATP) channels in NO-mediated vasodilation of retinal arterioles in rats. In vivo, the retinal vasodilator responses were assessed by measuring changes in the diameter of retinal arterioles from ocular fundus images. Intravitreal injection of 4-aminopyridine (a K_V channel inhibitor), but not glibenclamide (a K_ATP channel blocker), significantly attenuated the retinal vasodilator response to the NO donor (±)-(E)-4-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexenamide (NOR3). Intravitreal injection of indomethacin (a non-selective cyclooxygenase inhibitor) also reduced the NOR3-induced retinal vasodilator response. The combination of 4-aminopyridine and indomethacin produced a greater reduction in the NOR3-induced response than either agent alone. 4-Aminopyridine had no significant effect on pinacidil (a K_ATP channel opener)-induced response. These results suggest that the vasodilatory effects of NO are mediated, at least in part, through the activation of 4-aminopyridine-sensitive K_V channels in the retinal arterioles of rats. NO exerts its dilatory effect on the retinal vasculature of rats through at least two mechanisms, activation of the K_V channels and enhancement of prostaglandin production.

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.

Ischemic Heart Disease and Heart Failure: Role of Coronary Ion Channels

Heart failure is a complex syndrome responsible for high rates of death and hospitalization. Ischemic heart disease is one of the most frequent causes of heart failure and it is normally attributed to coronary artery disease, defined by the presence of one or more obstructive plaques, which determine a reduced coronary blood flow, causing myocardial ischemia and consequent heart failure. However, coronary obstruction is only an element of a complex pathophysiological process that leads to myocardial ischemia. In the literature, attention paid to the role of microcirculation, in the pathophysiology of ischemic heart disease and heart failure, is growing. Coronary microvascular dysfunction determines an inability of coronary circulation to satisfy myocardial metabolic demands, due to the imbalance of coronary blood flow regulatory mechanisms, including ion channels, leading to the development of hypoxia, fibrosis and tissue death, which may determine a loss of myocardial function, even beyond the presence of atherosclerotic epicardial plaques. For this reason, ion channels may represent the link among coronary microvascular dysfunction, ischemic heart disease and consequent heart failure.

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.

Endothelium-Dependent Vasorelaxant Effect of Prunus Persica Branch on Isolated Rat Thoracic Aorta

Peach (Prunus persica (L.) Batsch) is a popular fruit consumed by people worldwide, owing to its pleasant flavor and high mineral nutrient content. A few plants from the genus Prunus, such as Prunus yedoensis, Prunus cerasus, and Prunus serotina have shown vasorelaxant and vasodilatory effects, to date, no study has investigated the vasorelaxation effects of the P. persica branch extract (PPE). The vasorelaxant effect of PPE was endothelium-dependent, and it was related to the NO-sGC-cGMP, vascular prostacyclin, and muscarinic receptor transduction pathway. K⁺ channels, such as the BK_Ca, K_V, and K_ATP channels, were partially associated with PPE-induced vasorelaxation. PPE was effective in relaxing serotonin (5-HT)- or angiotensin II-induced contraction; furthermore, PPE attenuated Ca²⁺-induced vasoconstriction by IP₃ receptors in the SR membrane, but its vasorelaxant effect was not associated with the influx of extracellular Ca²⁺ via receptor-operative Ca²⁺ channels or voltage-dependent Ca²⁺ channels. Recognizing the rising use of functional foods for hypertension treatment, our findings imply that PPE may be a natural antihypertensive agent.

Membrane Lipid-K IR 2.x Channel Interactions Enable Hemodynamic Sensing in Cerebral Arteries

Objective—

Inward rectifying K + (K IR ) channels are present in cerebral arterial smooth muscle and endothelial cells, a tandem arrangement suggestive of a dynamic yet undiscovered role for this channel. This study defined whether distinct pools of cerebral arterial K IR channels were uniquely modulated by membrane lipids and hemodynamic stimuli.

Approach and Results—

A Ba 2+ -sensitive K IR current was isolated in smooth muscle and endothelial cells of rat cerebral arteries; molecular analyses subsequently confirmed K IR 2.1/K IR 2.2 mRNA and protein expression in both cells. Patch-clamp electrophysiology next demonstrated that each population of K IR channels was sensitive to key membrane lipids and hemodynamic stimuli. In this regard, endothelial K IR was sensitive to phosphatidylinositol 4,5-bisphosphate content, with depletion impairing the ability of laminar shear stress to activate this channel pool. In contrast, smooth muscle K IR was sensitive to membrane cholesterol content, with sequestration blocking the ability of pressure to inhibit channel activity. The idea that membrane lipids help confer shear stress and pressure sensitivity of K IR channels was confirmed in intact arteries using myography. Virtual models integrating structural/electrical observations reconceptualized K IR as a dynamic regulator of membrane potential working in concert with other currents to set basal tone across a range of shear stresses and intravascular pressures.

Conclusions—

The data show for the first time that specific membrane lipid-K IR interactions enable unique channel populations to sense hemodynamic stimuli and drive vasomotor responses to set basal perfusion in the cerebral circulation.

Myocardial Ischemia and Diabetes Mellitus: Role of Oxidative Stress in the Connection between Cardiac Metabolism and Coronary Blood Flow

Ischemic heart disease (IHD) has several risk factors, among which diabetes mellitus represents one of the most important. In diabetic patients, the pathophysiology of myocardial ischemia remains unclear yet: some have atherosclerotic plaque which obstructs coronary blood flow, others show myocardial ischemia due to coronary microvascular dysfunction in the absence of plaques in epicardial vessels. In the cross-talk between myocardial metabolism and coronary blood flow (CBF), ion channels have a main role, and, in diabetic patients, they are involved in the pathophysiology of IHD. The exposition to the different cardiovascular risk factors and the ischemic condition determine an imbalance of the redox state, defined as oxidative stress, which shows itself with oxidant accumulation and antioxidant deficiency. In particular, several products of myocardial metabolism, belonging to oxidative stress, may influence ion channel function, altering their capacity to modulate CBF, in response to myocardial metabolism, and predisposing to myocardial ischemia. For this reason, considering the role of oxidative and ion channels in the pathophysiology of myocardial ischemia, it is allowed to consider new therapeutic perspectives in the treatment of IHD.

D. russelii Venom Mediates Vasodilatation of Resistance Like Arteries via Activation of Kv and KCa Channels

Russell's viper (Daboia russelii) venom causes a range of clinical effects in humans. Hypotension is an uncommon but severe complication of Russell's viper envenoming. The mechanism(s) responsible for this effect are unclear. In this study, we examined the cardiovascular effects of Sri Lankan D. russelii venom in anaesthetised rats and in isolated mesenteric arteries. D. russelii venom (100 μg/kg, i.v.) caused a 45 ± 8% decrease in blood pressure within 10 min of administration in anaesthetised (100 μg/kg ketamine/xylazine 10:1 ratio, i.p.) rats. Venom (1 ng/mL⁻1 μg/mL) caused concentration-dependent relaxation (EC50 = 145.4 ± 63.6 ng/mL, Rmax = 92 ± 2%) in U46619 pre-contracted rat small mesenteric arteries mounted in a myograph. Vasorelaxant potency of venom was unchanged in the presence of the nitric oxide synthase inhibitor, L-NAME (100 µM), or removal of the endothelium. In the presence of high K⁺ (30 mM), the vasorelaxant response to venom was abolished. Similarly, blocking voltage-dependent (Kv: 4-aminopryidine; 1000 µM) and Ca2+-activated (KCa: tetraethylammonium (TEA; 1000 µM); SKCa: apamin (0.1 µM); IKCa: TRAM-34 (1 µM); BKCa; iberiotoxin (0.1 µM)) K⁺ channels markedly attenuated venom-induced relaxation. Responses were unchanged in the presence of the ATP-sensitive K⁺ channel blocker glibenclamide (10 µM), or H1 receptor antagonist, mepyramine (0.1 µM). Venom-induced vasorelaxtion was also markedly decreased in the presence of the transient receptor potential cation channel subfamily V member 4 (TRPV4) antagonist, RN-1734 (10 µM). In conclusion, D. russelii-venom-induced hypotension in rodents may be due to activation of Kv and KCa channels, leading to vasorelaxation predominantly via an endothelium-independent mechanism. Further investigation is required to identify the toxin(s) responsible for this effect.

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.

Ion Channels in Pulmonary Hypertension: A Therapeutic Interest?

Pulmonary arterial hypertension (PAH) is a multifactorial and severe disease without curative therapies. PAH pathobiology involves altered pulmonary arterial tone, endothelial dysfunction, distal pulmonary vessel remodeling, and inflammation, which could all depend on ion channel activities (K⁺, Ca²⁺, Na⁺ and Cl^-). This review focuses on ion channels in the pulmonary vasculature and discusses their pathophysiological contribution to PAH as well as their therapeutic potential in PAH.

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.

Involvement of the NO/sGC/cGMP/K+ channels pathway in vascular relaxation evoked by two non-quinazoline α1-adrenoceptor antagonists

The aim of this study was to explore the α₁-adrenoceptor-independent mechanisms involved in the vasorelaxant properties of two non-quinazoline α₁-adrenoceptors antagonists (MH-76 and MH-79). Endothelium intact and endothelium denuded rat aorta was contracted with 1 μM phenylephrine to plateau, and the vasodilatory effect of MH-76 and MH-79 was examined in the absence or presence of inhibitors of the different signal transduction pathways. cGMP concetration was measured in rat aorta (enzyme immunoassay kit). In human aortic endothelial cells (HAEC) NO production was examined using a DAF-FM DA fluorescent indicator, whereas in human aortic smooth muscle cells the influence of the title compounds on K⁺ efflux was evaluated. The vasorelaxant effect of MH-76 and MH-79 was attenuated by endothelium removal, N_ω-Nitro-l-arginine methyl ester (L-NAME) and 1H-[1,2,4]Oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) pretreatment to the level characteristic for α₁-adrenoreceptor blocking activity. In addition, the MH-76 and MH-79 induced relaxation was reduced by K⁺ channels blockers. In endothelium intact rat aorta, MH-76 and MH-79 caused an increase in cGMP level, whereas in HAEC they increased NO generation. In contrast, the reference, quinazoline based α₁-antagonist prazosin, did not influence NO production. Our findings suggest that the mechanisms underlying the vasodilatory properties of non-quinazoline based α₁-adrenoceptors antagonists MH-76 and MH-79 involve not only α₁-adrenoceptor blocking activity but also the activation of the endothelial NO-cGMP signalling pathway and the subsequent opening of K⁺ channels. Our studies show that such double mechanism of action is superior to pure α₁-adrenoceptor blockade, and may be considered as a promising alternative for the prevention and treatment of cardiovascular diseases.

The expression and function of KCNQ potassium channels in human chorionic plate arteries from women with normal pregnancies and pre-eclampsia

Pre-eclampsia is associated with altered maternal and placental vascular reactivity. Kv7 channels (encoded by KCNQ 1–5 genes) are a potential contributor to the regulation of vascular tone in CPAs (chorionic plate arteries) during normal pregnancy. The aim of this study is to establish the expression profile of KCNQ subunits in CPAs taken from women with preeclampsia or normotensive women and to examine the functional relevance of the Kv7 channels on an altered expression profile of KCNQ subunits. The effects of Kv7 channel modulators on CPAs were investigated by tension measurement. Quantitative PCR experiments were used to analyze the expression of KCNQ genes. Western blotting and immunofluorescence were both used to analyze the protein expression of Kv7 channels. Finally, in CPAs from normotensive women, the Kv7 channel blocker XE991 increased arterial basal tone and U46619-induced contraction, and pre-contracted CPAs (10⁻⁷ M U46619) exhibited significant relaxation following treatment with Retigabine(Kv7.2–7.5 activator) and BMS-204352(Kv7.2–7.5 activator). However, ICA-27243(selective KCNQ2 and KCNQ3 activator) and ML277(selective KV7.1 activator) had no significant effect on tension in the pre-contracted CPAs. Conversely, compared with CPAs from normotensive women, the effects of XE991 on basal tone and agonist (U46619)-induced contractions in CPAs from women with preeclampsia were markedly attenuated. Moreover, the relaxation effects of Retigabine and BMS-204352 on pre-contracted CPA vessels from women with pre-eclampsia were also markedly down-regulated. Interestingly, the relaxation ability of ICA-27243 in pre-contracted CPA vessels in women with pre-eclampsia was enhanced. The mRNA of KCNQ3 was specifically up-regulated, whereas those for KCNQ4 and KCNQ5 were down-regulated in CPAs from women with pre-eclampsia compared with those in normotensive women. Similar observations were found in a subsequent analysis of protein expression of KCNQ genes 3–5. Thus, down-regulated Kv7 channel function in tension regulation of CPAs in women with pre-eclampsia could be associated with considerably altered expression profiles of Kv7 subunits.

Acidosis potentiates endothelium-dependent vasorelaxation and gap junction communication in the superior mesenteric artery

Extracellular pH is an important physiological determinant of vascular tone that is normally maintained within 7.35-7.45. Any change outside this range leads to severe pathological repercussions. We investigated the unknown effects of extracellular acidosis on relaxation in the superior mesenteric artery (SMA) of goat. SMA rings were employed to maintain isometric contractions at extracellular pH (pH_o) 7.4 and 6.8. We analyzed the effect of acidosis (pH_o 6.8) compared to physiological pH (pH_o 7.4) on three signaling mediators of endothelium-dependent hyperpolarization: nitric oxide (NO), prostaglandin I₂ (PGI₂), and myoendothelial gap junctions (MEGJ). NO and cyclic guanosine monophosphate (cGMP) levels were compared between normal and acidic pH. Quantitative real-time PCR (qPCR) studies determined the change in expression of vascular connexin (Cx), Cx37, Cx40, and Cx43. Under acidosis, acetyl choline-induced relaxation was augmented in an endothelium-dependent manner via eNOS-NO-cGMP signaling. Conversely, at normal pH, acetyl choline-induced vasorelaxation was mediated primarily via COX-PGI₂ pathway. The functional activity of MEGJ was increased under acidosis as evident from increased sensitivity of connexin blockers and upregulated gene and protein expression of connexins. In conclusion, acetyl choline-induced augmented vasorelaxation under acidosis is mediated by NOS-NO-cGMP, with a partial role of MEGJ as EDH mediators in the SMA. Present data suggest a novel role of connexin as therapeutic targets to attenuate the detrimental effect of acidosis on vascular tone.

Regulation, signalling and functions of hormonal peptides in pulmonary vascular remodelling during hypoxia

Hypoxic state affects organism primarily by decreasing the amount of oxygen reaching the cells and tissues. To adjust with changing environment organism undergoes mechanisms which are necessary for acclimatization to hypoxic stress. Pulmonary vascular remodelling is one such mechanism controlled by hormonal peptides present in blood circulation for acclimatization. Activation of peptides regulates constriction and relaxation of blood vessels of pulmonary and systemic circulation. Thus, understanding of vascular tone maintenance and hypoxic pulmonary vasoconstriction like pathophysiological condition during hypoxia is of prime importance. Endothelin-1 (ET-1), atrial natriuretic peptide (ANP), and renin angiotensin system (RAS) function, their receptor functioning and signalling during hypoxia in different body parts point them as disease markers. In vivo and in vitro studies have helped understanding the mechanism of hormonal peptides for better acclimatization to hypoxic stress and interventions for better management of vascular remodelling in different models like cell, rat, and human is discussed in this review.

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.

Maxi-K channel (BKCa) activity veils the myogenic tone of mesenteric artery in rats

Arterioles and small arteries change their tone in response to transmural pressure changes, called myogenic tone (MT). In comparison to the branches of cerebral arteries (CA) showing prominent MT, the third branches of mesenteric arteries (MA) with similar diameters show weaker MT. Here, we aimed to analyze the electrophysiological differences responsible for the weaker MT in MA (MT_MA) than MT in CA (MT_CA). We measured ionic current using patch clamp in isolated MA smooth muscle cells (MASMCs) and CA smooth muscle cells (CASMCs) of rats. MT was analyzed using video analysis of pressurized small arteries. Quantitative‐PCR (q‐PCR) and immunofluorescence confocal microscopy were used to compare the mRNA and protein expression level of big‐conductance Ca²⁺‐activated K⁺ channel (BK_Ca) subunits (Slo1α and Sloβ1). Whole‐cell patch clamp study revealed higher density of voltage‐operated Ca²⁺ channel current (I_CaV) in the MASMCs than in CASMCs. Although voltage‐gated K⁺ channel current (I_Kv) was also higher in MASMCs, treatment with Kv inhibitor (4‐aminopyridine) did not affect MT_MA. Interestingly, BK_Ca current density and the frequency of spontaneous transient outward currents (STOCs) were consistently higher in MASMCs than in CASMCs. Inside‐out patch clamp showed that the Ca²⁺‐sensitivity of BK_Ca is higher in MASMCs than in CASMCs. Iberiotoxin, a selective BK_Ca inhibitor, augmented MT_MA by a larger extent than MT_CA. Although q‐PCR analysis did not reveal a significant difference of mRNAs for Slo1α and Sloβ1, immunofluorescence image suggested higher expression of Slo1α in MASMCs than in CASMCs. Despite the large I_CaV density, the high activities of BK_Ca including the more frequent STOCs in MASMCs veils the potentially strong MT_MA.

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.

Alterations of voltage-dependent K(+) channels in the mesenteric artery during the early and chronic phases of diabetes

This study investigated the alteration of voltage-dependent K(+) (Kv) channels in mesenteric arterial smooth muscle cells from control (Long-Evans Tokushima Otsuka [LETO]) and diabetic (Otsuka Long-Evans Tokushima Fatty [OLETF]) rats during the early and chronic phases of diabetes. We demonstrated alterations in the mesenteric Kv channels during the early and chronic phase of diabetes using the patch-clamp technique, the arterial tone measurement system, and RT-PCR in Long-Evans Tokushima (LETO; for control) and Otsuka Long-Evans Tokushima Fatty (OLETF; for diabetes) type 2 diabetic model rats. In the early phase of diabetes, the amplitude of mesenteric Kv currents induced by depolarizing pulses was greater in OLETF rats than in LETO rats. The contractile response of the mesenteric artery induced by the Kv inhibitor, 4-aminopyridine (4-AP), was also greater in OLETF rats. The expression of most Kv subtypes- including Kv1.1, Kv1.2, Kv1.4, Kv1.5, Kv1.6, Kv2.1, Kv3.2, Kv4.1, Kv4.3, Kv5.1, Kv6.2, Kv8.1, Kv9.3, and Kv10.1-were increased in mesenteric arterial smooth muscle from OLETF rats compared with LETO rats. However, in the chronic phase of diabetes, the Kv current amplitude did not differ between LETO and OLETF rats. In addition, the 4-AP-induced contractile response of the mesenteric artery and the expression of Kv subtypes did not differ between the two groups. The increased Kv current amplitude and Kv channel-related contractile response were attributable to the increase in Kv channel expression during the early phase of diabetes. The increased Kv current amplitude and Kv channel-related contractile response were reversed during the chronic phase of diabetes.

Kv1.3 channels facilitate the connection between metabolism and blood flow in the heart

The connection between metabolism and flow in the heart, metabolic dilation, is essential for cardiac function. We recently found redox-sensitive Kv1.5 channels play a role in coronary metabolic dilation; however, more than one ion channel likely plays a role in this process as animals null for these channels still showed limited coronary metabolic dilation. Accordingly, we examined the role of another Kv1 family channel, the energetically linked Kv1.3 channel, in coronary metabolic dilation. We measured myocardial blood flow (contrast echocardiography) during norepinephrine-induced increases in cardiac work (heart rate x mean arterial pressure) in WT, WT mice given correolide (preferential Kv1.3 antagonist), and Kv1.3-null mice (Kv1.3-/- ). We also measured relaxation of isolated small arteries mounted in a myograph. During increased cardiac work, myocardial blood flow was attenuated in Kv1.3-/- and in correolide-treated mice. In isolated vessels from Kv1.3-/- mice, relaxation to H2 O2 was impaired (vs WT), but responses to adenosine and acetylcholine were equivalent to WT. Correolide reduced dilation to adenosine and acetylcholine in WT and Kv1.3-/- , but had no effect on H2 O2 -dependent dilation in vessels from Kv1.3-/- mice. We conclude that Kv1.3 channels participate in the connection between myocardial blood flow and cardiac metabolism.

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.

Cell-cell communication in the vessel wall

Intercellular communication between cells within the blood vessel wall plays an important role in the control of artery diameter. The endothelial cells lining the lumen of arteries can evoke smooth muscle hyperpolarization both by the release of a factor (EDHF) and by direct cell-cell coupling through gap junctions. Hyperpolarizing current can spread rapidly to cause widespread vasodilatation, and thus increase blood flow to that segment. In addition to the spread of current, small molecules, such as Ca2+, can also pass between cells, but at a much reduced rate. Instead of co-ordinating changes in diameter, intercellular Ca2+ signalling acts to amplify and, in special cases, modulate vascular responses. Together, direct cell-cell communication enables the blood vessel wall to act as a functional syncytium, which is influenced by surrounding tissues and nerves, and blood constituents.

Iptakalim influences the proliferation and apoptosis of human pulmonary artery smooth muscle cells

The aim of the present study was to determine the effect of an ATP-sensitive K+ (KATP) channel opener iptakalim (IPT) on the proliferation and apoptosis of human pulmonary artery smooth muscle cells (HPASMCs), and examine the potential value of IPT to hypoxic pulmonary hyper-tension (HPH) at a cellular level. HPASMCs were divided into the control, ET-1, ET-1+IPT and ET-1+IPT+glibenclamide (GLI) groups. GLI was administered 30 min prior to ET-1 and IPT. The 4 groups were incubated with corresponding reagents for 24 h. Cell viability was evaluated using a CCK-8 assay, cell proliferation by 5-ethynyl-2'-deoxyuridine (EdU) incorporation assay, and cell apoptosis via the expression of apoptosis-related proteins, i.e., Bcl-2-associated X protein (Bax) and B-cell lymphoma 2 (Bcl-2) using western blotting. We incubated HPASMCs with varying concentrations of ET-1 for 24, 48 and 72 h, and found that cell survival rate was increased in a dose-dependent manner (P<0.05) rather than in a time-dependent manner (P>0.05). After co-incubation of HPASMCs with varying concentrations of IPT and ET-1 for 24 h, the cell survival rate was decreased in a dose-dependent manner. The cell survival rate in the IPT+ET-1 group was significantly lower than that in the ET-1 group (P<0.05). The cell viability (P<0.05) and proliferation (P<0.05) in the ET-1 group were higher than those in the control group, and the expression of Bax/Bcl-2 was lower than the control group (P<0.05). The cell viability (P<0.05) and proliferation (P<0.05) in the ET-1+IPT group were lower than those in the ET-1 group, and the expression of Bax/Bcl-2 was higher than that in the ET-1 group (P<0.05). The cell viability (P<0.05) and proliferation (P<0.05) in the ET-1+IPT+GLI group were higher than those in the ET-1+IPT group, and the expression of Bax/Bcl-2 was lower than that in the ET-1+IPT group (P<0.05). In conclusion, IPT inhibited ET-1‑induced HPASMC proliferation and promoted cell apoptosis. Thus, it may play an important role in the treatment of HPH.

Mechanism of vasorelaxation induced by eupatorin in the rats aortic ring

Previous studies demonstrated that eupatorin content in Orthosiphon stamineus fractions correlated with their vasorelaxation activity. Even with previous studies, there is still very little information on the vasorelaxation effect of eupatorin, and not many scientific studies had been carried out. Therefore, the present study was designed to investigate the vasorelaxation activity and mechanism of action of eupatorin. The vasorelaxation activity and the underlying mechanisms of eupatorin was evaluated on thoracic aortic rings isolated from Sprague Dawley rats. Eupatorin caused the relaxation of aortic rings pre-contracted with phenylephrine with and without endothelium (pD2=6.66±0.13, EMAX=99.72±6.39%; pD2=6.10±0.22, EMAX=65.78±8.01%), and also the relaxation of endothelium-intact aortic rings pre-contracted with potassium chloride (pD2=6.20±0.30, EMAX=71.89±12.25%). In the presence of Nω-nitro-l-arginine methyl ester (pD2<4.60, EMAX=24.91±6.39%), methylene blue (pD2=6.05±0.38, EMAX=66.79±9.69%), ODQ (pD25.84±0.32, EMAX=60.47±9.6%), indomethacin (pD2=6.27±0.21, EMAX=76.03±9.45%), tetraethylammonium (pD2=6.09±0.35, EMAX=69.35±11.31%), 4-aminopyridine (pD2=6.34±0.12, EMAX=76±6.1%), barium chloride (pD2=6.47±0.14, EMAX=79.61±10.02%), atropine (pD2=6.36±0.29, EMAX=86.47±12.95%) and propranolol (pD2=6.49±0.26, EMAX=83.2±12.01%), relaxation stimulated by eupatorin was significantly reduced. Eupatorin was also found to be active in reducing Ca(2+) release from sarcoplasmic reticulum and in blocking calcium channels. The present study demonstrates the vasorelaxation effect of eupatorin involving NO/sGC/cGMP and indomethacin pathways, calcium and potassium channels, and muscarinic and beta-adrenergic receptors.

Ca2+ dependent but PKC independent signalling mediates UTP induced contraction of rat mesenteric arteries

Uridine triphosphate (UTP) can be released from damaged cells to cause vasoconstriction. Although UTP is known to act through P2Y receptors and PLC activation in vascular smooth muscle, the role of PKC in generating the response is somewhat unclear. Here we have used Tat-linked membrane permeable peptide inhibitors of PKC to assess the general role of PKC and also of specific isoforms of PKC in the UTP induced contraction of rat mesenteric artery. We examined the effect of PKC inhibition on UTP induced contraction, increased cytoplasmic Ca²⁺ and reduction of K⁺ currents and found that PKC inhibition caused a relatively small attenuation of contraction but had little effect on changes in cytoplasmic Ca²⁺. UTP attenuation of both voltage-gated (K_v) and ATP-dependent (K_ATP) K⁺ currents was abolished when intracellular Ca²⁺ was decreased from 100 to 20 nM. PKC inhibition reduced slightly the ability of UTP to attenuate K_v currents but had no effect on K_ATP current inhibition. In conclusion, both UTP induced contraction of mesenteric artery and the inhibition of K_v and K_ATP currents of mesenteric artery smooth muscle cells by UTP are relatively independent of PKC activation; furthermore, the inhibition of both K_v and K_ATP currents requires intracellular Ca²⁺.

The class III anti-arrhythmic agent, amiodarone, inhibits voltage-dependent K(+) channels in rabbit coronary arterial smooth muscle cells

We examined the inhibitory effect of amiodarone, a class III anti-arrhythmic agent, on voltage-dependent K(+) (Kv) currents in freshly isolated rabbit coronary arterial smooth muscle cells, using a whole-cell patch clamp technique. Amiodarone inhibited Kv currents in a concentration-dependent manner, with a half-maximal inhibitory concentration (IC50) value of 3.9 ± 1.44 μM and a Hill coefficient of 0.45 ± 0.14. Amiodarone did not have a significant effect on the steady-state activation of Kv channels, but shifted the inactivation current toward a more negative potential. Application of consecutive pulses progressively augmented the amiodarone-induced Kv channel inhibition. Another class III anti-arrhythmic agent, dofetilide, did not inhibit the Kv current or change the inhibitory effect of amiodarone on Kv channels. Therefore, these results strongly suggest that amiodarone inhibits Kv currents in a concentration- and state-dependent manner.

Equol increases cerebral blood flow in rats via activation of large-conductance Ca(2+)-activated K(+) channels in vascular smooth muscle cells

The present study was designed to investigate the effect of equol on cerebral blood flow and the underlying molecular mechanisms. The regional cerebral blood flow in parietal lobe of rats was measured by using a laser Doppler flowmetry. Isolated cerebral basilar artery and mesenteric artery rings from rats were used for vascular reactivity measurement with a multi wire myography system. Outward K(+) current in smooth muscle cells of cerebral basilar artery, large-conductance Ca(2+)-activated K(+) (BK) channel current in BK-HEK 293 cells stably expressing both human α (hSlo)- and β1-subunits, and hSlo channel current in hSlo-HEK 293 cells expressing only the α-subunit of BK channels were recorded with whole cell patch-clamp technique. The results showed that equol significantly increased regional cerebral blood flow in rats, and produced a concentration-dependent but endothelium-independent relaxation in rat cerebral basilar arteries. Both paxilline and iberiotoxin, two selective BK channel blockers, significantly inhibited equol-induced vasodilation in cerebral arteries. Outward K(+) currents in smooth muscle cells of cerebral basilar artery were increased by equol and fully reversed by washout or blockade of BK channels with iberiotoxin. Equol remarkably enhanced human BK current in BK-HEK 293 cells, but not hSlo current in hSlo-HEK 293 cells, and the increase was completely abolished by co-application of paxilline. Our findings provide the first information that equol selectively stimulates BK channel current by acting on its β1 subunit, which may in turn contribute to the equol-mediated vasodilation and cerebral blood flow increase.

Effect of 4-chloro-7-trifluoromethyl-10H-benzo[4,5]furo[3,2-b]indole-1-carboxylic acid on the intraurethral pressure in a rat model of benign prostatic hyperplasia

OBJECTIVES

To investigate the effect of 4-chloro-7-trifluoromethyl-10H-benzo[4,5]furo[3,2-b]indole-1-carboxylic acid, a new benzofuroindole derivative, on the intraurethral pressure in a rat model of benign prostatic hyperplasia.

METHODS

Benign prostatic hyperplasia was induced by testosterone and 17β-estradiol, which were administered intramuscularly once a day for 12 weeks. The effects of 4-chloro-7-trifluoromethyl-10H-benzo[4,5]furo[3,2-b]indole-1-carboxylic acid and tamsulosin on the intraurethral pressure induced by the electrostimulation of hypogastric nerves after a single intravenous injection of 4-chloro-7-trifluoromethyl-10H-benzo[4,5]furo[3,2-b]indole-1-carboxylic acid (10 mg/kg) or tamsulosin (10 μg/kg) were evaluated in a benign prostatic hyperplasia model. The electrostimulation-induced intraurethral pressure was measured just before and after the injection of 4-chloro-7-trifluoromethyl-10H-benzo[4,5]furo[3,2-b]indole-1-carboxylic acid. Bodyweight and genitourinary organ weights were recorded, and serums and tissues were subjected to hormone assays and histopathology. In addition, the expression of α1-adrenoceptors in the prostate was measured by western blotting.

RESULTS

The benign prostatic hyperplasia groups showed increased prostatic index, increased concentrations of testosterone, free testosterone and estradiol in serum, and increased epithelial thickness of the prostate. An injection of 4-chloro-7-trifluoromethyl-10H-benzo[4,5]furo[3,2-b]indole-1-carboxylic acid or tamsulosin significantly inhibited the elevation of electrostimulation-induced intraurethral pressure. In addition, 4-chloro-7-trifluoromethyl-10H-benzo[4,5]furo[3,2-b]indole-1-carboxylic acid did not cause a significant change in the blood pressure compared with tamsulosin. While the benign prostatic hyperplasia group showed increased the expression of α1-adrenoceptors, the 4-chloro-7-trifluoromethyl-10H-benzo[4,5]furo[3,2-b]indole-1-carboxylic acid or tamsulosin injection into a rat model of benign prostatic hyperplasia decreased the expression of α1-adrenoceptors.

CONCLUSIONS

These findings show that 4-chloro-7-trifluoromethyl-10H-benzo[4,5]furo[3,2-b]indole-1-carboxylic acid might be beneficial for lowering the intraurethral pressure associated with benign prostatic hyperplasia, and it could represent a therapeutic option for benign prostatic hyperplasia patients.

ABCC9/SUR2 in the brain: Implications for hippocampal sclerosis of aging and a potential therapeutic target

The ABCC9 gene and its polypeptide product, SUR2, are increasingly implicated in human neurologic disease, including prevalent diseases of the aged brain. SUR2 proteins are a component of the ATP-sensitive potassium ("KATP") channel, a metabolic sensor for stress and/or hypoxia that has been shown to change in aging. The KATP channel also helps regulate the neurovascular unit. Most brain cell types express SUR2, including neurons, astrocytes, oligodendrocytes, microglia, vascular smooth muscle, pericytes, and endothelial cells. Thus it is not surprising that ABCC9 gene variants are associated with risk for human brain diseases. For example, Cantu syndrome is a result of ABCC9 mutations; we discuss neurologic manifestations of this genetic syndrome. More common brain disorders linked to ABCC9 gene variants include hippocampal sclerosis of aging (HS-Aging), sleep disorders, and depression. HS-Aging is a prevalent neurological disease with pathologic features of both neurodegenerative (aberrant TDP-43) and cerebrovascular (arteriolosclerosis) disease. As to potential therapeutic intervention, the human pharmacopeia features both SUR2 agonists and antagonists, so ABCC9/SUR2 may provide a "druggable target", relevant perhaps to both HS-Aging and Alzheimer's disease. We conclude that more work is required to better understand the roles of ABCC9/SUR2 in the human brain during health and disease conditions.