Cardiac ATP-sensitive K+ channels: regulation by intracellular nucleotides and K+ channel-opening drugs

1995 ◽  
Vol 269 (3) ◽  
pp. C525-C545 ◽  
Author(s):  
A. Terzic ◽  
A. Jahangir ◽  
Y. Kurachi
Keyword(s):  
Katp Channel ◽  
Molecular Mechanisms ◽  
Enzymatic Reaction ◽  
Katp Channels ◽  
Cardiac Cells ◽  
K Channel ◽  
Channel Activity ◽  
Pharmacological Agents ◽  
Channel Opening ◽  
Main Regulator

ATP-sensitive K+ (KATP) channels are present at high density in membranes of cardiac cells where they regulate cardiac function during cellular metabolic impairment. KATP channels have been implicated in the shortening of the action potential duration and the cellular loss of K+ that occurs during metabolic inhibition. KATP channels have been associated with the cardioprotective mechanism of ischemia-related preconditioning. Intracellular ATP (ATPi) is the main regulator of KATP channels. ATPi has two functions: 1) to close the channel (ligand function) and 2) in the presence of Mg2+, to maintain the activity of KATP channels (presumably through an enzymatic reaction). KATP channel activity is modulated by intracellular nucleoside diphosphates that antagonize the ATPi-induced inhibition of channel opening or induce KATP channels to open. How nucleotides will affect KATP channels depends on the state of the channel. K+ channel-opening drugs are pharmacological agents that enhance KATP channel activity through different mechanisms and have great potential in the management of cardiovascular conditions. KATP channel activity is also modulated by neurohormones. Adenosine, through the activation of a GTP-binding protein, antagonizes the ATPi-induced channel closure. Understanding the molecular mechanisms that underlie KATP channel regulation should prove essential to further define the function of KATP channels and to elucidate the pharmacological regulation of this channel protein. Since the molecular structure of the KATP channel has now become available, it is anticipated that major progress in the KATP channel field will be achieved.

Regulation of ATP-sensitive K+ channels by ATP and nucleotide diphosphate in rabbit portal vein

1994 ◽  
Vol 266 (5) ◽  
pp. H1687-H1698 ◽  
Author(s):  
M. Kamouchi ◽  
K. Kitamura
Keyword(s):  
Portal Vein ◽  
Katp Channel ◽  
Single Channel ◽  
Katp Channels ◽  
K Channel ◽  
Channel Activity ◽  
Rabbit Portal Vein ◽  
Internal Side ◽  
The Right ◽  
Single Channel Currents

The modulation of ATP-sensitive K+ (KATP)-channel activity was investigated by recording single-channel currents in isolated smooth muscle cells from rabbit portal vein. K(+)-channel openers (KCOs; pinacidil, lemakalim, and nicorandil) induced burstlike openings of single KATP channels in the cell-attached configuration. After patch excision, KATP channels showed "run-down" phenomenon in the presence of KCOs, but subsequent application of Mg-ATP (1 mM) restored KATP-channel activity. Removal of Mg-ATP resulted in transient augmentation of KATP currents, which eventually decayed out. Nucleotide diphosphates (NDPs; GDP, ADP, UDP, IDP, and CDP) also induced channel reopening in the presence of KCOs, which was markedly enhanced by addition of Mg2+ in millimolar concentrations at the internal side of the membrane. The dose-response relation between ATP and the UDP-induced KATP-channel activity was shifted to the right in the presence of Mg2+ (2 mM). These results suggest that intracellular ATP, NDPs, and Mg2+ regulate the channel state of KATP channels (operative and inoperative states) and that KCOs open KATP channels only in the operative state.

scholarly journals Mechanism of action of K channel openers on skeletal muscle KATP channels. Interactions with nucleotides and protons.

1996 ◽  
Vol 107 (4) ◽  
pp. 489-502 ◽  
Author(s):  
C Forestier ◽  
J Pierrard ◽  
M Vivaudou
Keyword(s):  
Skeletal Muscle ◽  
Molecular Mechanisms ◽  
Structural Diversity ◽  
Katp Channels ◽  
Quantitative Agreement ◽  
Dissociation Rate ◽  
K Channel ◽  
Channel Activity ◽  
Patch Clamp Technique ◽  
Free Nucleotides

The molecular mechanisms underlying the actions of K channel openers (KCOs) on KATP channels were studied with the patch clamp technique in excised inside-out patches from frog skeletal muscle fibers. Benzopyran KCOs (levcromakalim and SR 47063) opened channels partially blocked by ATP, ADP, or ATP gamma s, with and without Mg2+, but they had no effects in the absence of internal nucleotides, even after channel activity had significantly declined because of rundown. The effects of KCOs could therefore be attributed solely to a competitive interaction between KCOs and nucleotides, as confirmed by observations that ATP decreased the apparent affinity for KCOs and that, conversely, KCOs decreased ATP or ADP sensitivity. Protons antagonized the action of the non-benzopyran KCOs, pinacidil and aprikalim, by enhancing their dissociation rate. This effect resembled the effect of acidification on benzopyran KCOs (Forestier, C., Y. Depresle, and M. Vivaudou. FEBS Lett. 325:276-280, 1993), suggesting that, in spite of their structural diversity, KCOs could act through the same binding sites. Detailed analysis of the inhibitory effects of protons on channel activity induced by levcromakalim or SR 47063 revealed that, in the presence of 100 microM ATP, this effect developed steeply between pH 7 and 6 and was half maximal at pH 6.6. These results are in quantitative agreement with an allosteric model of the KATP channel possessing four protonation sites, two nucleotidic sites accessible preferentially to Mg(2+)-free nucleotides, and one benzopyran KCO site. The structural implications of this model are discussed.

Effects of thiol-modifying agents on KATP channels in guinea pig ventricular cells

1995 ◽  
Vol 269 (5) ◽  
pp. H1625-H1633 ◽  
Author(s):  
W. A. Coetzee ◽  
T. Y. Nakamura ◽  
J. F. Faivre
Keyword(s):  
Katp Channel ◽  
Single Channel ◽  
Katp Channels ◽  
Channel Activity ◽  
Nitrobenzoic Acid ◽  
Ventricular Cells ◽  
Channel Opening ◽  
Sh Group ◽  
Constant Potential ◽  
High Degree

ATP-sensitive K+ (KATP) channels are thought only to open during conditions of metabolic impairment (e.g., myocardial ischemia). However, the regulation of KATP channel opening during ischemia remains poorly understood. We tested whether thiol (SH) group oxidation, which is known to occur during ischemia, may be involved in KATP channel regulation. Inside-out membrane patches were voltage clamped at a constant potential (O mV) in asymmetrical K+ solutions. The effects of compounds that specifically modify SH groups [p-chloromercuri-phenylsulfonic acid (pCMPS), 5-5'-dithio-bis(2-nitrobenzoic acid) [DTNB], and thimerosal] were tested. The membrane-impermeable compound, pCMPS (> or = 5 microM), caused a quick and irreversible inhibition of KATP channel activity. The reducing agent, dl-dithiothreitol (DTT) (3 mM) was able to reverse this inhibition. DTNB (500 microM) caused a rapid, but spontaneously reversible, block of KATP channel activity. After DTNB, no change was observed in single channel conductance. Oxidized glutathione (GSSG, 3 mM) did not block KATP channel activity. Thimerosal (100-500 microM) induced a DTT-reversible block of partially rundown KATP channels, or channels that underwent complete rundown; these channels were reactivated with trypsin (1 mg/ml). Thimerosal did not block KATP channels that had a high degree of activity. However, the ATP sensitivity was decreased; the concentration of ATP needed to half-maximally inhibit the channel (Ki) was increased from 47 +/- 12 to 221 +/- 35 microM (n = 6, P < 0.05). This was not due to a spontaneous change with time.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Ligand-insensitive State of Cardiac ATP-sensitive K+ Channels

1998 ◽  
Vol 111 (2) ◽  
pp. 381-394 ◽  
Author(s):  
Alexey E. Alekseev ◽  
Peter A. Brady ◽  
Andre Terzic
Keyword(s):  
Kinetic Model ◽  
Katp Channel ◽  
Katp Channels ◽  
Cardiac Cell ◽  
Channel Activity ◽  
K Channels ◽  
Channel Interaction ◽  
Channel Opening ◽  
State Kinetic ◽  
Allosteric Model

The mechanism by which ATP-sensitive K+ (KATP) channels open in the presence of inhibitory concentrations of ATP remains unknown. Herein, using a four-state kinetic model, we found that the nucleotide diphosphate UDP directed cardiac KATP channels to operate within intraburst transitions. These transitions are not targeted by ATP, nor the structurally unrelated sulfonylurea glyburide, which inhibit channel opening by acting on interburst transitions. Therefore, the channel remained insensitive to ATP and glyburide in the presence of UDP. “Rundown” of channel activity decreased the efficacy with which UDP could direct and maintain the channel to operate within intraburst transitions. Under this condition, the channel was sensitive to inhibition by ATP and glyburide despite the presence of UDP. This behavior of the KATP channel could be accounted for by an allosteric model of ligand-channel interaction. Thus, the response of cardiac KATP channels towards inhibitory ligands is determined by the relative lifetime the channel spends in a ligand-sensitive versus -insensitive state. Interconversion between these two conformational states represents a novel basis for KATP channel opening in the presence of inhibitory concentrations of ATP in a cardiac cell.

scholarly journals Cantu syndrome-associated SUR2 (ABCC9) mutations in distinct structural domains result in KATP channel gain-of-function by differential mechanisms

2017 ◽  
Author(s):  
Conor McClenaghan ◽  
Alex Hanson ◽  
Monica Sala-Rabanal ◽  
Helen I. Roessler ◽  
Dragana Josifova ◽  
...  
Keyword(s):  
Katp Channel ◽  
Molecular Mechanisms ◽  
Cardiovascular Disorder ◽  
Major Effect ◽  
Channel Activity ◽  
Gain Of Function ◽  
Structural Domains ◽  
Equivalent Position ◽  
Genes Encoding ◽  
Patch Clamp Electrophysiology

AbstractThe complex cardiovascular disorder Cantu Syndrome arises from gain-of-function mutations in either KCNJ8 or ABCC9, the genes encoding the Kir6.1 and SUR2 subunits of ATP-sensitive potassium (KATP) channels. Recent reports indicate that such mutations can increase channel activity by multiple molecular mechanisms. In this study, we determine the mechanism by which KATP function is altered by several mutations in distinct structural domains of SUR2: D207E in the intracellular L0-linker and Y985S, G989E, M1060I, and R1154Q/W in TMD2. Mutations were engineered at their equivalent position in rat SUR2A (D207E, Y981S, G985E, M1056I and R1150Q/W) and functional effects were investigated using macroscopic rubidium (86Rb+) efflux assays and patch clamp electrophysiology. The results show that D207E increases KATP activity by increasing intrinsic stability of the open state, whilst the cluster of Y981S/G985E/M1056I mutations, as well as R1150Q/W, augment Mg-nucleotide activation. The response of mutant channels to inhibition by the sulfonylurea drug glibenclamide, a potential pharmacotherapy for CS, was also tested. There was no major effect on glibenclamide sensitivity for the D207E, Y981S, G985E or M1056I mutations, but glutamine and tryptophan substitution at R1150 resulted in significant decreases in potency.

scholarly journals Recent Advances in Pharmacological and Non-Pharmacological Strategies of Cardioprotection

2019 ◽  
Vol 20 (16) ◽  
pp. 4002 ◽  
Author(s):  
Afonso Caricati-Neto ◽  
Paolo Ruggero Errante ◽  
Francisco Sandro Menezes-Rodrigues
Keyword(s):  
Intracellular Signaling ◽  
Molecular Mechanisms ◽  
Heart Diseases ◽  
Cardiac Cells ◽  
Ischemia And Reperfusion ◽  
Protective Response ◽  
Pharmacological Agents ◽  
Ischemic Heart Diseases ◽  
Intracellular Signaling Pathways ◽  
Recent Advances

Ischemic heart diseases (IHD) are the leading cause of death worldwide. Although the principal form of treatment of IHD is myocardial reperfusion, the recovery of coronary blood flow after ischemia can cause severe and fatal cardiac dysfunctions, mainly due to the abrupt entry of oxygen and ionic deregulation in cardiac cells. The ability of these cells to protect themselves against injury including ischemia and reperfusion (I/R), has been termed “cardioprotection”. This protective response can be stimulated by pharmacological agents (adenosine, catecholamines and others) and non-pharmacological procedures (conditioning, hypoxia and others). Several intracellular signaling pathways mediated by chemical messengers (enzymes, protein kinases, transcription factors and others) and cytoplasmic organelles (mitochondria, sarcoplasmic reticulum, nucleus and sarcolemma) are involved in cardioprotective responses. Therefore, advancement in understanding the cellular and molecular mechanisms involved in the cardioprotective response can lead to the development of new pharmacological and non-pharmacological strategies for cardioprotection, thus contributing to increasing the efficacy of IHD treatment. In this work, we analyze the recent advances in pharmacological and non-pharmacological strategies of cardioprotection.

ATP-sensitive K channel modulation by products of PLA2 action in the insulin-secreting HIT cell line

1995 ◽  
Vol 268 (1) ◽  
pp. C181-C190 ◽  
Author(s):  
G. T. Eddlestone
Keyword(s):  
Arachidonic Acid ◽  
Cell Line ◽  
Katp Channel ◽  
Tumor Cell Line ◽  
Cyclooxygenase Inhibitors ◽  
K Channel ◽  
Channel Activity ◽  
Membrane Phospholipids ◽  
Venom Component ◽  
Inside Out

Insulin secretion from the islets of Langerhans may be initiated or potentiated by increased phospholipase A2 (PLA2) activity. This patch-clamp study of the insulin-secreting HIT tumor cell line assessed whether inhibition of the ATP-sensitive potassium (KATP) channel, which modulates the secretion-associated beta-cell electrical activity, contributes to the secretory response to PLA2. Exogenous PLA2 (100-1,000 mU/ml) reversibly suppressed KATP channel activity in excised inside-out patches. Similarly, mellitin (0.5-5 micrograms/ml), a bee venom component that increases phospholipid susceptibility to metabolism by PLA2, suppressed KATP channel activity, suggesting that PLA2 is present in excised patches. Adding low concentrations of particular lysophospholipids or arachidonic acid also reduced KATP channel activity in excised inside-out patches. In cell-attached patches, the lysophospholipids had a similar effect, whereas arachidonic acid caused channel stimulation; this latter effect was reversed by cyclooxygenase inhibitors. A recently identified ATP-stimulated PLA2 in beta-cells has been proposed as an important mediator of stimulus-secretion coupling in response to nutrients. The present data illustrating that initial products of PLA2 action on membrane phospholipids reduce KATP channel activity indicate a mechanism that may contribute an early stimulatory signal in this pathway. The observation that metabolism of arachidonate via the cyclooxygenase pathway causes KATP channel stimulation demonstrates a potential counterregulatory mechanism.

scholarly journals Regulation of Cloned Atp-Sensitive K Channels by Adenine Nucleotides and Sulfonylureas

2001 ◽  
Vol 118 (4) ◽  
pp. 391-406 ◽  
Author(s):  
Scott A. John ◽  
James N. Weiss ◽  
Bernard Ribalet
Keyword(s):  
Katp Channel ◽  
Adenine Nucleotides ◽  
Katp Channels ◽  
Functional Coupling ◽  
Sulfonylurea Receptor ◽  
K Channels ◽  
Channel Regulation ◽  
Channel Opening ◽  
Insight Into ◽  
Positively Charged

KATP channels, comprised of the pore-forming protein Kir6.x and the sulfonylurea receptor SURx, are regulated in an interdependent manner by adenine nucleotides, PIP2, and sulfonylureas. To gain insight into these interactions, we investigated the effects of mutating positively charged residues in Kir6.2, previously implicated in the response to PIP2, on channel regulation by adenine nucleotides and the sulfonylurea glyburide. Our data show that the Kir6.2 “PIP2-insensitive” mutants R176C and R177C are not reactivated by MgADP after ATP-induced inhibition and are also insensitive to glyburide. These results suggest that R176 and R177 are required for functional coupling to SUR1, which confers MgADP and sulfonylurea sensitivity to the KATP channel. In contrast, the R301C and R314C mutants, which are also “PIP2-insensitive,” remained sensitive to stimulation by MgADP in the absence of ATP and were inhibited by glyburide. Based on these findings, as well as previous data, we propose a model of the KATP channel whereby in the presence of ATP, the R176 and R177 residues on Kir6.2 form a specific site that interacts with NBF1 bound to ATP on SUR1, promoting channel opening by counteracting the inhibition by ATP. This interaction is facilitated by binding of MgADP to NBF2 and blocked by binding of sulfonylureas to SUR1. In the absence of ATP, since KATP channels are not blocked by ATP, they do not require the counteracting effect of NBF1 interacting with R176 and R177 to open. Nevertheless, channels in this state remain activated by MgADP. This effect may be explained by a direct stimulatory interaction of NBF2/MgADP moiety with another region of Kir6.2 (perhaps the NH2 terminus), or by NBF2/MgADP still promoting a weak interaction between NBF1 and Kir6.2 in the absence of ATP. The region delimited by R301 and R314 is not involved in the interaction with NBF1 or NBF2, but confers additional PIP2 sensitivity.

scholarly journals The Opening of ATP-Sensitive K+ Channels Protects H9c2 Cardiac Cells Against the High Glucose-Induced Injury and Inflammation by Inhibiting the ROS-TLR4-Necroptosis Pathway

2017 ◽  
Vol 41 (3) ◽  
pp. 1020-1034 ◽  
Author(s):  
Weijie Liang ◽  
Meiji Chen ◽  
Dongdan Zheng ◽  
Jianhao Li ◽  
Mingcai Song ◽  
...  
Keyword(s):  
Cell Viability ◽  
Inflammatory Cytokines ◽  
High Glucose ◽  
Katp Channel ◽  
Channel Blocker ◽  
Cardiac Injury ◽  
Cardiac Cells ◽  
Mitochondrial Katp Channel ◽  
Channel Opening ◽  
Pre Treatment

Background/Aims: Hyperglycemia activates multiple signaling molecules, including reactive oxygen species (ROS), toll-like receptor 4 (TLR4), receptor-interacting protein 3 (RIP3, a kinase promoting necroptosis), which mediate hyperglycemia-induced cardiac injury. This study explored whether inhibition of ROS-TLR4-necroptosis pathway contributed to the protection of ATP-sensitive K+ (KATP) channel opening against high glucose-induced cardiac injury and inflammation. Methods: H9c2 cardiac cells were treated with 35 mM glucose (HG) to establish a model of HG-induced insults. The expression of RIP3 and TLR4 were tested by western blot. Generation of ROS, cell viability, mitochondrial membrane potential (MMP) and secretion of inflammatory cytokines were measured as injury indexes. Results: HG increased the expression of TLR4 and RIP3. Necrostatin-1 (Nec-1, an inhibitor of necroptosis) or TAK-242 (an inhibitor of TLR4) co-treatment attenuated HG-induced up-regulation of RIP3. Diazoxide (DZ, a mitochondrial KATP channel opener) or pinacidil (Pin, a non-selective KATP channel opener) or N-acetyl-L-cysteine (NAC, a ROS scavenger) pre-treatment blocked the up-regulation of TLR4 and RIP3. Furthermore, pre-treatment with DZ or Pin or NAC, or co-treatment with TAK-242 or Nec-1 attenuated HG-induced a decrease in cell viability, and increases in ROS generation, MMP loss and inflammatory cytokines secretion. However, 5-hydroxy decanoic acid (5-HD, a mitochondrial KATP channel blocker) or glibenclamide (Gli, a non-selective KATP channel blocker) pre-treatment did not aggravate HG-induced injury and inflammation. Conclusion: KATP channel opening protects H9c2 cells against HG-induced injury and inflammation by inhibiting ROS-TLR4-necroptosis pathway.

scholarly journals Anti-diabetic drug binding site in a mammalian KATP channel revealed by Cryo-EM

eLife ◽  
2017 ◽  
Vol 6 ◽  
Author(s):  
Gregory M Martin ◽  
Balamurugan Kandasamy ◽  
Frank DiMaio ◽  
Craig Yoshioka ◽  
Show-Ling Shyng
Keyword(s):  
Binding Sites ◽  
Katp Channel ◽  
Katp Channels ◽  
Binding Pocket ◽  
Drug Binding ◽  
Channel Activity ◽  
Nucleotide Binding Domain ◽  
High Affinity ◽  
Drug Binding Site ◽  
First Time

Sulfonylureas are anti-diabetic medications that act by inhibiting pancreatic KATP channels composed of SUR1 and Kir6.2. The mechanism by which these drugs interact with and inhibit the channel has been extensively investigated, yet it remains unclear where the drug binding pocket resides. Here, we present a cryo-EM structure of a hamster SUR1/rat Kir6.2 channel bound to a high-affinity sulfonylurea drug glibenclamide and ATP at 3.63 Å resolution, which reveals unprecedented details of the ATP and glibenclamide binding sites. Importantly, the structure shows for the first time that glibenclamide is lodged in the transmembrane bundle of the SUR1-ABC core connected to the first nucleotide binding domain near the inner leaflet of the lipid bilayer. Mutation of residues predicted to interact with glibenclamide in our model led to reduced sensitivity to glibenclamide. Our structure provides novel mechanistic insights of how sulfonylureas and ATP interact with the KATP channel complex to inhibit channel activity.

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