ATP-sensitive potassium channels:novel potential roles in Parkinson's disease

The ATP-sensitive potassium（KATP）channels which extensively distribute in diverse tissues（e.g.vascular smooth muscle,cardiac cells,and pancreas）are well-established for characteristics like vasodilatation,myocardial protection against ischemia,and insulin secretion.The aim of this review is to get insight into the novel roles of KATPchannels in Parkinson＇s disease（PD）,with consideration of the specificities KATPchannels in the central nervous system（CNS）, such as the control of neuronal excitability,action potential,mitochondrial function and neurotransmitter release.

Effects of Mitochondrial ATP-sensitive K^+ Channel on Protein Kinase C Pathway and Airway Smooth Muscle Cell Proliferation in Asthma

The effects of ATP-sensitive mitochondrial K + channel(mitoK ATP) on mitochondrial membrane potential(Δψm),cell proliferation and protein kinase C alpha(PKCα) expression in airway smooth muscle cells(ASMCs) were investigated.Thirty-six Sprague-Dawley(SD) rats were immunized with saline(controls) or ovalbumin(OVA) with alum(asthma models).ASMCs were cultured from the lung of control and asthma rats.ASMCs were treated with diazoxide(the potent activator of mitoK ATP) or 5-hydroxydencanote(5-HD,the inhibitor of mitoK ATP).Rhodamine-123(R-123) was used to detect Δψm.The expression of PKCα protein was examined by using Western blotting,while PKCα mRNA expression was detected by using real-time PCR.The proliferation of ASMCs was measured by MTT assay and cell cycle analysis.In diazoxide-treated normal ASMCs,the R-123 fluorescence intensity,protein and mRNA levels of PKCα,MTT A values and percentage of cells in S phase were markedly increased as compared with untreated controls.The ratio of G 0 /G 1 cells was decreased(P<0.05) in diazoxide-treated ASMCs from normal rats.However,there were no significant differences between the ASMCs from healthy rats treated with 5-HD and the normal control group.In untreated and diazoxide-treated ASMCs of asthmatic rats,the R-123 fluorescence intensity,protein and mRNA levels of PKCα,MTT A values and the percentage of cells in S phase were increased in comparison to the normal control group.Furthermore,in comparison to ASMCs from asthmatic rats,these values were considerably increased in asthmatic group treated with diazoxide(P<0.05).After exposure to 5-HD for 24 h,these values were decreased as compared with asthma control group(P<0.05).In ASMCs of asthma,the signal transduction pathway of PKCα may be involved in cell proliferation,which is induced by the opening of mitoK ATP and the depolarization of Δψm.

Localization of ATP-sensitive K^+ channel subunits in rat liver

BACKGROUND ATP-sensitive K^+(KATP)channels were originally found in cardiac myocytes by Noma in 1983.KATP channels were formed by potassium ion-passing poreforming subunits(Kir6.1,Kir6.2)and regulatory subunits SUR1,SU2A and SUR2B.A number of cells and tissues have been revealed to contain these channels including hepatocytes,but detailed localization of these subunits in different types of liver cells was still uncertain.AIM To investigate the expression of KATP channel subunits in rat liver and their localization in different cells of the liver.METHODS Rabbit anti-rat SUR1 peptide antibody was raised and purified by antigen immunoaffinity column chromatography.Four of Sprague-Dawley rats were used for liver protein extraction for immunoblot analysis,seven of them were used for immunohistochemistry both for the ABC method and immunofluorescence staining.Four of Wistar rats were used for the isolation of hepatic stellate cells(HSCs)and Kupffer cells for both primary culture and immunocytochemistry.RESULTS Immunoblot analysis showed that the five kinds of KATP channel subunits,i.e.Kir6.1,Kir6.2,SUR1,SUR2A,and SUR2B,were detected in liver.Immunohistochemical staining showed that Kir6.1 and Kir6.2 were weakly to moderately expressed in parenchymal cells and sinusoidal lining cells,while SUR1,SUR2A,and SUR2B were mainly localized to sinusoidal lining cells,such as HSCs,Kupffer cells,and sinusoidal endothelial cells.Immunoreactivity for SUR2A and SUR2B was expressed in the hepatocyte membrane.Double immunofluorescence staining further showed that the pore-forming subunits Kir6.1 and/or Kir6.2 colocalized with GFAP in rat liver sections and primary cultured HSCs.These KATP channel subunits also colocalized with CD68 in liver sections and primary cultured Kupffer cells.The SUR subunits colocalized with GFAP in liver sections and colocalized with CD68 both in liver sections and primary cultured Kupffer cells.In addition,five KATP channel subunits colocalized with SE-1 in sinusoidal endothelial cells.CONCLUSION Observations from the present study indicated that KATP channel subunits expressed in rat liver and the diversity of KATP channel subunit composition might form different types of KATP channels.This is applicable to hepatocytes,HSCs,various types of Kupffer cells and sinusoidal endothelial cells.

Effect of G_(αq/11) Protein and ATP-sensitive Potassium Channels on Ischemic Preconditioning in Rat Hearts

Objectives To investigate the effect of Gαq/11 signaling pathway and ATP-sensitive potassium channel ( KATP channel ) on ischemic preconditioning (IPC) protection in rat hearts. Methods Two series of experiments were performed in Wistar rat hearts. In the first series of experiment, ischemic preconditioning was induced by left anterior descending occlusion (three, 5 min episodes separated by 5 min of reperfusion), ischemia-reperfusion injury was induced by 30 min coronary artery occlusion followed by 90 min reperfusion. Hemodynamics, infarct size and scores of ventricular arrhythmias were measured. The expression of Gαq/11 protein in the heart was measured by Western blot analysis in the second series. Results Ischemic preconditioning rats showed decreased infarct size and scores of ventricular arrhythmia vs non-IP control rats. The effect of IPC was significantly attenuated by glibenclamide (1 mg/kg, ip), a nonselective KATP channel inhibitor. IPC caused a significant increase in the expression of Gαq/11 protein. Conclusions Activations of Gαq/11 signal pathway and KATP channel played significant roles in the classical cardioprotection of ischemic precon-ditioning rat heart and might be an important mechanism of signal transduction pathway during the ischemic preconditioning.

Expression levels of K_(ATP)channel subunits and morphological changes in the mouse liver after exposure to radiation

BACKGROUND ATP sensitive K+(K_(ATP))channels are ubiquitously distributed in various of cells and tissues,including the liver.They play a role in the pathogenesis of myocardial and liver ischemia.AIM To evaluate the radiation-induced changes in the expression of K_(ATP)channel subunits in the mouse liver to understand the potential role of K_(ATP)channels in radiation injury.METHODS Adult C57BL/6 mice were randomly exposed toγ-rays at 0 Gy(control,n=2),0.2 Gy(n=6),1 Gy(n=6),or 5 Gy(n=6).The livers were removed 3 and 24 h after radiation exposure.Hematoxylin and eosin staining was used for morphological observation;immunohistochemical staining was applied to determine the expression of K_(ATP)channel subunits in the liver tissue.RESULTS Compared with the control group,the livers exposed to 0.2 Gyγ-ray showed an initial increase in the expression of Kir6.1 at 3 h,followed by recovery at 24 h after exposure.Exposure to a high dose of 5.0 Gy resulted in decreased expression of Kir6.1 and increased expression of SUR2B at 24 h.However,the expression of Kir6.2,SUR1,or SUR2A had no remarkable changes at 3 and 24 h after exposure to any of these doses.CONCLUSION The expression levels of Kir6.1 and SUR2B in mouse liver changed differently in response to different radiation doses,suggesting a potential role for them in radiation-induced liver injury.

Beneficial effects of adenosine triphosphate-sensitive K^+ channel opener on liver ischemia/reperfusion injury

AIM: To investigate the effect of diazoxide administration on liver ischemia/reperfusion injury.

Adenosine triphosphate-sensitive potassium channel opener protects PC12 cells against hypoxia-induced apoptosis through PI3K/Akt and Bcl-2 signaling pathways

Although previous studies have shown the neuroprotective effects of the adenosine triphosphate （ATP）-sensitive potassium （KATP） channel opener against ischemic neuronal damage, little is known about the mechanisms involved. Phosphatidylinositol-3 kinase （PI3K）/v-akt murine thy-moma viral oncogene homolog （Akt） and Bcl-2 are thought to be important factors that mediate neuroprotection. The present study investigated the effects of KATP openers on hypoxia-induced PC12 cell apoptosis, as well as mRNA and protein expression of Akt and Bcl-2. Results demon-strated that pretreatment of PC12 cells with pinacidil, a KATP opener, resulted in decreased PC12 cell apoptosis following hypoxia, as detected by Annexin-V fluorescein isothiocyanate/ propidium iodide double staining flow cytometry. In addition, mRNA and protein expression of phosphorylated Akt （p-Akt） and Bcl-2 increased, as detected by immunofluorescence, Western blot analysis, and reverse-transcription polymerase chain reaction. The protective effect of this preconditioning was attenuated by glipizide, a selective KATP blocker. These results demonstrate for the first time that the protective mechanisms of KATP openers on PC12 cell apoptosis following hypoxia could result from activation of the PI3K/Akt signaling pathway, which further activates expression of the downstream Bcl-2 gene.

Iptakalim,an ATP-sensitive potassium channel opener,confers neuroprotection against cerebral ischemia/reperfusion injury in rats by protecting neurovascular unit cells

Objective:To investigate the role of iptakalim,an ATP-sensitive potassium channel opener,in transient cerebral ischemia/reperfusion (I/R) injury and its involved mechanisms.Methods:Intraluminal occlusion of middle cerebral artery (MCAO) in a rat model was used to investigate the effect of iptakalim at different time points.Infarct volume was measured by staining with 2,3,5-triphenyltetrazolium chloride,and immunohistochemistry was used to evaluate the expressions of Bcl-2 and Bax.In vitro,neurovascular unit (NVU) cells,including rat primary cortical neurons,astrocytes,and cerebral microvascular endothelial cells,were cultured and underwent oxygen-glucose deprivation (OGD).The protective effect of iptakalim on NVU cells was investigated by cell viability and injury assessments,which were measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and release of lactate dehydrogenase.Caspase-3,Bcl-2 and Bax mRNA expressions were evaluated by real-time polymerase chain reaction (PCR).Results:Administration of iptakalim 0 or 1 h after reperfusion significantly reduced infarct volumes,improved neurological scores,and attenuated brain edema after cerebral I/R injury.Iptakalim treatment (0 h after reperfusion) also reduced caspase-3 expression and increased the ratio of Bcl-2 to Bax by immunohistochemistry.Iptakalim inhibited OGD-induced cell death in cultured neurons and astrocytes,and lactate dehydrogenase release from cerebral microvascular endothelial cells.Iptakalim reduced mRNA expression of caspase-3 and increased the ratio of Bcl-2 to Bax in NVU cells.Conclusions:Iptakalim confers neuroprotection against cerebral I/R injury by protecting NVU cells via inhibiting of apoptosis.

Structure of an ATP-sensitive potassium channel(K_(ATP))

Subject Code:C05 With the support by the National Natural Science Foundation of China,the collaborative research team led by Prof.Chen Lei(陈雷)at the State Key Laboratory of Membrane Biology,Institute of Molecular Medicine,Peking-Tsinghua Center for Life Sciences,Beijing Key Laboratory of Cardiometabolic

Urocortin, the neuropeptide, inhibits the viability of ECV304 cells and rat vascular smooth muscle cells

Objective: This study aims to investigate the effects of urocortin (Ucn) on the viability of endothelial cells (ECV304) and rat vascular muscle cells (VSMC). Methods: Rat aortic VSMC were isolated from the rats' thoracic aorta. We studied the effect of Ucn on the viability of ECV304 cells and VSMC by using a tetrazolium (MTT) assay.Results: Ucn (10 -7 mol/L) inhibited the viability of ECV304 cells and VSMC. Inhibition rates are 13% and 15%, respectively(P<0.05, compared with Control). This inhibition was not dependent on the affecting time and was not affected by the addition of ATP-sensitive potassium channel (KATP channel) blocker, glybenclamide (Gly, 10 mol/L). Conclusion: Ucn inhibits the viability of ECV304 and VSMC. Our results suggest that Ucn may be a new vasoactive agent and may have a beneficial effect in the process of vascular remodeling (VR).

Opiate-induced constipation related to activation of small intestine opioid μ2-receptors

AIM： To investigate the role of opioid p-receptor subtype in opiate-induced constipation （OIC）.METHODS： The effect of Ioperamide on intestinal transit was investigated in mice. Ileum strips were isolated from 12-wk-old male BALB/c mice for identification of isometric tension. The ileum strips were precontracted with 1 μmol/L acetylcholine （ACh）. Then, decrease in muscle tone （relaxation） was characterized after cumu- lative administration of 0.1-10μ~mol/L Ioperamide into the organ bath, for a concentration-dependent study. Specific blockers or antagonists were used for pretreat- ment to compare the changes in Ioperamide-induced relaxation.RESULTS： In addition to the delay in intestinal transit, Ioperamide produced a marked relaxation in isolated ileum precontracted with ACh, in a dose-dependent manner. This relaxation was abolished by cyprodime,a selective opioid p-receptor antagonist, but not modified by naloxonazine at a dose sufficient to block opioid μ-1 receptors. Also, treatment with opioid μ-1 receptor agonist failed to modify the muscle tone. Moreover, the relaxation by Ioperamide was attenuated by glibenclamide at a dose sufficient to block ATP-sensitive K^＋ （KATP） channels, and by protein kinase A （PKA） inhibitor, but was enhanced by an inhibitor of phosphodiesterase for cyclic adenosine monophosphate （cAMP）.CONCLUSION： Loperamide induces intestinal relaxa- tion by activation of opioid μ-2 receptors via the cAMP- PKA pathway to open KATp channels, relates to OIC.

Regulatory role of mitochondria in oxidative stress and atherosclerosis

Mitochondrial physiology and biogenesis play a crucial role in the initiation and progression of cardiovascular disease following oxidative stress-induced damage such as atherosclerosis(AST).Dysfunctional mitochondria caused by an increase in mitochondrial reactive oxygen species(ROS)production,accumulation of mitochondrial DNA damage,and respiratory chain deficiency induces death of endothelial/smooth muscle cells and favors plaque formation/rupture via the regulation of mitochondrial biogenesis-related genes such as peroxisome proliferator-activated receptorγcoactivator(PGC-1),although more detailed mechanisms still need further study.Based on the effect of healthy mitochondria produced by mitochondrial biogenesis on decreasing ROS-mediated cell death and the recent finding that the regulation of PGC-1 involves mitochon- drial fusion-related protein(mitofusin),we thus infer the regulatory role of mitochondrial fusion/fission balance in AST pathophysiology.In this review,the first section discusses the possible association between AST-inducing factors and the molecular regulatory mechanisms of mitochondrial biogenesis and dynamics,and explains the role of mitochondria-dependent regulation in cell apoptosis during AST development. Furthermore,nitric oxide has the Janus-faced effect by protecting vascular damage caused by AST while being a reactive nitrogen species(RNS)which act together with ROS to damage cells.Therefore,in the second section we discuss mitochondrial ATP-sensitive K+ channels,which regulate mitochondrial ion transport to maintain mitochondrial physiology,involved in the regulation of ROS/RNS production and their influence on AST/cardiovascular diseases(CVD).Through this review,we can further appreciate the multi-regulatory functions of the mitochondria involved in AST development.The understanding of these related mechanisms will benefit drug development in treating AST/CVD through targeted biofunctions of mitochondria.

Diazoxide preconditioning antagonizes cytotoxicity induced by epileptic seizures

Diazoxide, an activator of mitochondrial ATP-sensitive potassium channels, can protect neurons and astrocytes against oxidative stress and apoptosis. In this study, we established a cellular mode of epilepsy by culturing hippocampal neurons in magnesium-free medium, and used this to investigate effects of diazoxide preconditioning on the expression of inwardly rectifying potassium channel （Kir） subunits of the ATP-sensitive potassium. We found that neuronal viability was significantly reduced in the epileptic cells, whereas it was enhanced by diazoxide preconditioning. Double immunofluorescence and western blot showed a significant increase in the expression of Kir6.1 and Kir6.2 in epileptic cells, especially at 72 hours after seizures. Diazoxide pretreatment completely reversed this effect at 24 hours after seizures. In addition, Kir6.1 expression was significantly upregulated compared with Kir6.2 in hippocampal neurons after seizures. These findings indicate that diazoxide pretreatment may counteract epileptiform discharge-induced cytotoxicity by suppressing the expression of Kir subunits.

ATP敏感性钾通道的靶向治疗研究进展

ATP敏感性钾通道(ATP-sensitive K+channel,KATP通道)存在于心血管、神经、胰腺、胃肠道、生殖系统等多种组织中,在生理、病理过程中发挥重要作用,是许多疾病的治疗靶点。KATP通道受多种因素调控,是一种将膜兴奋性与细胞的代谢状态耦合的配体门控钾通道。

Effect of temperature on the activation of myocardial K_(ATP) channel in guinea pig ventricular myocytes: a pilot study by whole cell patch clamp recording

Background The myocardial ATP sensitive potassium channel （KATP channel） has been known for more than two decades, the properties of this channel have been intensively investigated, especially the myocardial protection effect by opening this channel. Numerous studies, including hypothermic, using KATP agonists to achieve a hyperpolarizing cardioplegic arrest, have shown a better myocardial protection than potassium arrest. However, there is no evidence showing that KATP channel could be opened by its agonists under profound hypothermia. We investigated the effect of temperature on activation of myocardial KATP channel by nicorandil.Methods Isolated ventricular myocytes were obtained by collagenase digestion of the hearts of guinea pigs and stored in KB solution at 4℃. With a steady ground current, the myocytes were perfused with 1 mmol/L nicorandil until a steady IKATP occurred. Then the cells were perfused with 1 mmol/L nicorandil plus 1 μmol/L glybenclamide. Currents signals were recorded on whole cells using patch clamp technique at several temperatures. The temperature of the bath solution around myocytes was monitored and was controlled at 4℃, 10℃, 20℃, 25℃ and 35℃ respectively. About 10 cells were tested at each temperature, the cells were considered useful only when the outward current could be induced by nicorandil and blocked by glybenclamide. All data were analyzed using Graphpad PRISM 3.0 （Graphpad, San Diego, CA, USA）. Nonlinear curve fitting was done in Clampfit （Axon） or Sigmaplot （SPSS）.Results At 4℃, 10℃, 20℃, 25℃ and 35℃, the time needed to open the myocardial KATP channel was （81.0±0） minutes, （50.54±11.7） minutes, （28.84±2.3） minutes, （9.4± 10.2） minutes and （2.3± 1.0） minutes respectively （P=0.003）. The linear relationship between temperature and time needed to open the channel was y （min） = （4348.790±124.277x）/60, where y （min） is time needed to open KATP channel, x is temperature, correlation coefficient r =-0.942 （P=0.00）, regression coefficient b =-124.277 （P=0.00）. The current densities among different temperatures were statistically different （P=0.022）, the current density was greater after the activation of KATP channel at higher temperatures. The lower the temperature, the fewer cells in which KATP channels could be opened. At 4℃, only one cell in which the KATP channel could be opened, took a quite long time （81 minutes）and the Ⅰ-Ⅴ curve was quite untypical.Conclusions KATP channel activated by nicorandil is temperature dependent and the temperature linearly related to time needed to open KATP channel; the lower the temperature, the longer the time needed to open channel and the smaller the current density. At profound hypothermia, it is difficult to activate KATP channels.

otassium channels in airway smooth muscle and airway hyperreactivity in asthma

Our knowledge of the physiology of ion channels has increased tremendously during the past 20 years because of the advances of the single-channel recording and molecular cloning techniques. More than 50 different identified potassium channels have already been found.1,2 They are distributed ubiquitously in wide variety of cells including airway smooth muscle （ASM） cells and inflammatory cells in airway such as eosinophils, basophils, macrophages and so on.3 Several types of K+ channels have been identified in ASM cells, e.g., a large-conductance, voltgage-dependent Ca2+-activated K+ channel(BKCa), a voltage-dependent delayed-rectifier K+ channel（Kv）, and an ATP-sensitve K+ channel(KATP).1 In such excitable cells,

Double-gating mechanism and diversity of an adenosine triphosphate (ATP)-sensitive K^+ channel in neurons acutely dissociated from rat neocortex

Classically, ion channels are classified into 2 groups: chemical-sensitive (ligand-gated) and voltage-sensitive channels. Single ATP-sensitive K+ (K-ATP) channel currents were recorded in acutely dissociated rat neo-cortical neurons using patch clamp technique. A type of K-ATP channel has been found to be gated not only by intra-cellular ATP, but also by membrane potential ( Vm) , and proved to be a novel mechanism underlying the gating of ion channels, namely bi-gating mechanism. The results also show that the K-ATP channels possess heterogeneity and di-versity. These types of K-ATP channels have been identified in 40.12% of all patches, which are different in activa-tion-threshold and voltage-sensitivity. The present experiment studied the type-3 K-ATP channel with a unitary con-ductance of about 80 pS in detail ( n = 15). Taking account of all the available data, a variety of K-ATP channels are suggested to exist in body, and one type of them is bi-gated by both chemical substances and membrane potentials. This property of the K-ATP channels may be related to their pathophysiblogical function.

Effects of gliclazide on myocardial protection of isolated type 2 diabetic rat heart afforded by ischemic preconditioning

The myocardial protection afforded by ischernic preconditioning （IPC） can alleviate ischemi- a-repel-fusion injury in normal rat heart. However, this myocardial protection is seldom studied in the type 2 diabetic rat with myocardial ischemia disease. In this study, we aimed to evaluate the effects of ATP-sensitive potassium channels （KATP channels） on IPC in the isolated type 2 diabetic rat heart and the role of the sul- fonylurea gliclazide. Methods Streptozotocin（STZ）-induced type 2 diabetic male Wistar rats with or without gliclazide （64 mg/kg body weight, orally） and age-matched non-diabetic control rats were used for all studies. The isolated hearts were perfused with Langendorff＇s system under the constant flow, pressure and tempera- ture conditions with Kreb＇s-Henseleit solution （K-H）. After 5 minutes of balance peffusion, these rats were randomly divided into six groups： non-diabetic control rats without IPC （CIR） ; non-diabetic control rats with IPC （CIP）; diabetic rats without 1PC （DIR）; diabetic rats with IPC （DIP）; gliclazide-treated diabetic rats without IPC （GIR）; and gliclazide-treated diabetic rats with IPC （GIP）. Groups CIR, DIR, and GIR were subjected to 30-rain global ischemia and 60-rain reperfusion for induction of ischemia/reperfusion injury. Groups CIP, DIP, and GIP were given three cycles of 5-min ischemia and 5-rain reperfusion as IPC, and then ischemia/reperfusion injury program was implemented. Extent of ischemia/reperfusion injury was measured in terms of the release of lactate dehydrogenase （LDH）, creatine kinase （CK）, and creatin kinase-MB （CK- MB） in coronary effluent. After perfusion, Kir6.2 and SUR2A mRNA expressions in the myocardial tissue were characterized by fluorescent quantitative real-time PCR method, and Kir6.2 and SUR2A protein expres- sions were assessed by immunohistochemistry. Result In non-diabetic control rats, the release of LDH, CK, and CK-MB in coronary effluent markedly decreased with IPC compared with No-IPC （P 〈 0.05）, but not in diabetic rats. However, in gliclazide-treated diabetic rats, IPC-induced decrease in the release of LDH, CK, and CK-MB was restored compared with No-IPC （P 〈 0.05）. The expressions of Kir6.2 both at mRNA and protein levels in CIP were significantly higher than those in CIR. There was no significant difference in theexpression of Kir6.2 and SUR2A both at mRNA and protein levels between DIP and DIR. However, the expression of Kir6.2 both at mRNA and protein levels was significantly higher in GIP than in GIR. No significant difference was detected in the mRNA expression level of SUR2A between the six groups. The expression of SUR2A at protein level was significantly higher in CIP than in CIR and in GIP than in GIR. Conclusions The cardioprotective effect of IPC is abolished in the isolated type 2 diabetic rats compared with non-diabetic control rats. However, to some extent, gliclazide can improve the myocardial protection of IPC against ischemia/reperfusion injury, thus suggesting that it is mediated mainly by KATP channels at mRNA or protein level, which provides a basis for further investigating the effects of KATP channels on IPC.