scholarly journals Muscle KATP Channels: Recent Insights to Energy Sensing and Myoprotection

2010 ◽  
Vol 90 (3) ◽  
pp. 799-829 ◽  
Author(s):  
Thomas P. Flagg ◽  
Decha Enkvetchakul ◽  
Joseph C. Koster ◽  
Colin G. Nichols
Keyword(s):  
Cell Metabolism ◽  
Katp Channels ◽  
Sulfonylurea Receptor ◽  
Channel Activity ◽  
Tissue Specific ◽  
Fiber Damage ◽  
Cellular Energetics ◽  
Muscle Types ◽  
Energy Sensing ◽  
The Cost

ATP-sensitive potassium (KATP) channels are present in the surface and internal membranes of cardiac, skeletal, and smooth muscle cells and provide a unique feedback between muscle cell metabolism and electrical activity. In so doing, they can play an important role in the control of contractility, particularly when cellular energetics are compromised, protecting the tissue against calcium overload and fiber damage, but the cost of this protection may be enhanced arrhythmic activity. Generated as complexes of Kir6.1 or Kir6.2 pore-forming subunits with regulatory sulfonylurea receptor subunits, SUR1 or SUR2, the differential assembly of KATP channels in different tissues gives rise to tissue-specific physiological and pharmacological regulation, and hence to the tissue-specific pharmacological control of contractility. The last 10 years have provided insights into the regulation and role of muscle KATP channels, in large part driven by studies of mice in which the protein determinants of channel activity have been deleted or modified. As yet, few human diseases have been correlated with altered muscle KATP activity, but genetically modified animals give important insights to likely pathological roles of aberrant channel activity in different muscle types.

scholarly journals Differential mechanisms of Cantú syndrome–associated gain of function mutations in the ABCC9 (SUR2) subunit of the KATP channel

2015 ◽  
Vol 146 (6) ◽  
pp. 527-540 ◽  
Author(s):  
Paige E. Cooper ◽  
Monica Sala-Rabanal ◽  
Sun Joo Lee ◽  
Colin G. Nichols
Keyword(s):  
Cell Metabolism ◽  
Katp Channels ◽  
Sulfonylurea Receptor ◽  
Membrane Excitability ◽  
Gain Of Function ◽  
Equivalent Position ◽  
Functional Consequences ◽  
Atp Inhibition ◽  
Patch Clamp Electrophysiology ◽  
Inwardly Rectifying

Cantú syndrome (CS) is a rare disease characterized by congenital hypertrichosis, distinct facial features, osteochondrodysplasia, and cardiac defects. Recent genetic analysis has revealed that the majority of CS patients carry a missense mutation in ABCC9, which codes for the sulfonylurea receptor SUR2. SUR2 subunits couple with Kir6.x, inwardly rectifying potassium pore-forming subunits, to form adenosine triphosphate (ATP)-sensitive potassium (KATP) channels, which link cell metabolism to membrane excitability in a variety of tissues including vascular smooth muscle, skeletal muscle, and the heart. The functional consequences of multiple uncharacterized CS mutations remain unclear. Here, we have focused on determining the functional consequences of three documented human CS-associated ABCC9 mutations: human P432L, A478V, and C1043Y. The mutations were engineered in the equivalent position in rat SUR2A (P429L, A475V, and C1039Y), and each was coexpressed with mouse Kir6.2. Using macroscopic rubidium (86Rb+) efflux assays, we show that KATP channels formed with P429L, A475V, or C1039Y mutants enhance KATP activity compared with wild-type (WT) channels. We used inside-out patch-clamp electrophysiology to measure channel sensitivity to ATP inhibition and to MgADP activation. For P429L and A475V mutants, sensitivity to ATP inhibition was comparable to WT channels, but activation by MgADP was significantly greater. C1039Y-dependent channels were significantly less sensitive to inhibition by ATP or by glibenclamide, but MgADP activation was comparable to WT. The results indicate that these three CS mutations all lead to overactive KATP channels, but at least two mechanisms underlie the observed gain of function: decreased ATP inhibition and enhanced MgADP activation.

scholarly journals Engineered interaction between SUR1 and Kir6.2 that enhances ATP sensitivity in KATP channels

2012 ◽  
Vol 140 (2) ◽  
pp. 175-187 ◽  
Author(s):  
Emily B. Pratt ◽  
Qing Zhou ◽  
Joel W. Gay ◽  
Show-Ling Shyng
Keyword(s):  
Cell Metabolism ◽  
Katp Channels ◽  
Dynamic Parameter ◽  
Sulfonylurea Receptor ◽  
Wild Type ◽  
Membrane Excitability ◽  
Close Proximity ◽  
Secretion Inhibition ◽  
Sulfonylurea Receptor 1 ◽  
Hallmark Feature

The ATP-sensitive potassium (KATP) channel consisting of the inward rectifier Kir6.2 and SUR1 (sulfonylurea receptor 1) couples cell metabolism to membrane excitability and regulates insulin secretion. Inhibition by intracellular ATP is a hallmark feature of the channel. ATP sensitivity is conferred by Kir6.2 but enhanced by SUR1. The mechanism by which SUR1 increases channel ATP sensitivity is not understood. In this study, we report molecular interactions between SUR1 and Kir6.2 that markedly alter channel ATP sensitivity. Channels bearing an E203K mutation in SUR1 and a Q52E in Kir6.2 exhibit ATP sensitivity ∼100-fold higher than wild-type channels. Cross-linking of E203C in SUR1 and Q52C in Kir6.2 locks the channel in a closed state and is reversible by reducing agents, demonstrating close proximity of the two residues. Our results reveal that ATP sensitivity in KATP channels is a dynamic parameter dictated by interactions between SUR1 and Kir6.2.

scholarly journals Regulation of KATP Channel Activity by Diazoxide and MgADP

1997 ◽  
Vol 110 (6) ◽  
pp. 643-654 ◽  
Author(s):  
S.-L. Shyng ◽  
T. Ferrigni ◽  
C.G. Nichols
Keyword(s):  
Katp Channel ◽  
Katp Channels ◽  
Nucleotide Binding ◽  
Sulfonylurea Receptor ◽  
Channel Activity ◽  
Nucleotide Hydrolysis ◽  
Inward Rectifier Potassium Channel ◽  
Hydrolysis Rates ◽  
Atp Inhibition

KATP channels were reconstituted in COSm6 cells by coexpression of the sulfonylurea receptor SUR1 and the inward rectifier potassium channel Kir6.2. The role of the two nucleotide binding folds of SUR1 in regulation of KATP channel activity by nucleotides and diazoxide was investigated. Mutations in the linker region and the Walker B motif (Walker, J.E., M.J. Saraste, M.J. Runswick, and N.J. Gay. 1982. EMBO [Eur. Mol. Biol. Organ.] J. 1:945–951) of the second nucleotide binding fold, including G1479D, G1479R, G1485D, G1485R, Q1486H, and D1506A, all abolished stimulation by MgADP and diazoxide, with the exception of G1479R, which showed a small stimulatory response to diazoxide. Analogous mutations in the first nucleotide binding fold, including G827D, G827R, and Q834H, were still stimulated by diazoxide and MgADP, but with altered kinetics compared with the wild-type channel. None of the mutations altered the sensitivity of the channel to inhibition by ATP4−. We propose a model in which SUR1 sensitizes the KATP channel to ATP inhibition, and nucleotide hydrolysis at the nucleotide binding folds blocks this effect. MgADP and diazoxide are proposed to stabilize this desensitized state of the channel, and mutations at the nucleotide binding folds alter the response of channels to MgADP and diazoxide by altering nucleotide hydrolysis rates or the coupling of hydrolysis to channel activation.

Pharmacology and modulation of KATP channels by protein kinase C and phosphatases in gallbladder smooth muscle

2000 ◽  
Vol 278 (5) ◽  
pp. C1031-C1037 ◽  
Author(s):  
T. A. Firth ◽  
G. M. Mawe ◽  
M. T. Nelson
Keyword(s):  
Smooth Muscle ◽  
Protein Kinase C ◽  
Protein Kinase ◽  
Mesenteric Artery ◽  
Kinase Activity ◽  
Katp Channels ◽  
Therapeutic Agents ◽  
Channel Activity ◽  
Kinase C ◽  
Muscle Types

ATP-sensitive K+ (KATP) channels exhibit pharmacological diversity, which is critical for the development of novel therapeutic agents. We have characterized KATP channels in gallbladder smooth muscle to determine how their pharmacological properties compare to KATP channels in other types of smooth muscle. KATP currents were measured in myocytes isolated from gallbladder and mesenteric artery. The potencies of pinacidil, diazoxide, and glibenclamide were similar in gallbladder and vascular smooth muscle, suggesting that the regions of the channel conferring sensitivity to these agents are conserved among smooth muscle types. Activators of protein kinase C (PKC), however, were less effective at inhibiting KATP currents in myocytes from gallbladder than mesenteric artery. The phosphatase inhibitor okadaic acid increased the efficacy of PKC activators and revealed ongoing basal activation of KATP channels by protein kinase A in gallbladder. These results suggest that phosphatases and basal kinase activity play an important role in controlling KATP channel activity.

scholarly journals Cryo-electron microscopy structures and progress toward a dynamic understanding of KATP channels

2018 ◽  
Vol 150 (5) ◽  
pp. 653-669 ◽  
Author(s):  
Michael C. Puljung
Keyword(s):  
Electron Microscopy ◽  
Ligand Binding ◽  
Adenine Nucleotide ◽  
Adenine Nucleotides ◽  
Cell Metabolism ◽  
Katp Channels ◽  
K Channel ◽  
Sulfonylurea Receptor ◽  
Binding Domains ◽  
Cryo Electron Microscopy

Adenosine triphosphate (ATP)–sensitive K+ (KATP) channels are molecular sensors of cell metabolism. These hetero-octameric channels, comprising four inward rectifier K+ channel subunits (Kir6.1 or Kir6.2) and four sulfonylurea receptor (SUR1 or SUR2A/B) subunits, detect metabolic changes via three classes of intracellular adenine nucleotide (ATP/ADP) binding site. One site, located on the Kir subunit, causes inhibition of the channel when ATP or ADP is bound. The other two sites, located on the SUR subunit, excite the channel when bound to Mg nucleotides. In pancreatic β cells, an increase in extracellular glucose causes a change in oxidative metabolism and thus turnover of adenine nucleotides in the cytoplasm. This leads to the closure of KATP channels, which depolarizes the plasma membrane and permits Ca2+ influx and insulin secretion. Many of the molecular details regarding the assembly of the KATP complex, and how changes in nucleotide concentrations affect gating, have recently been uncovered by several single-particle cryo-electron microscopy structures of the pancreatic KATP channel (Kir6.2/SUR1) at near-atomic resolution. Here, the author discusses the detailed picture of excitatory and inhibitory ligand binding to KATP that these structures present and suggests a possible mechanism by which channel activation may proceed from the ligand-binding domains of SUR to the channel pore.

Mechanism of Cardiac Sarcolemmal Adenosine Triphosphate–sensitive Potassium Channel Activation by Isoflurane in a Heterologous Expression System

2006 ◽  
Vol 105 (3) ◽  
pp. 534-540 ◽  
Author(s):  
Martin Bienengraeber ◽  
David C. Warltier ◽  
Zeljko J. Bosnjak ◽  
Anna Stadnicka
Keyword(s):  
Heterologous Expression ◽  
Adenosine Triphosphate ◽  
Katp Channel ◽  
Expression System ◽  
Katp Channels ◽  
Sulfonylurea Receptor ◽  
Channel Activity ◽  
Heterologous Expression System ◽  
Open Probability ◽  
Channel Activation

Background Activation of the cardiac sarcolemmal adenosine triphosphate-sensitive potassium (KATP) channel during metabolic stress initiates cellular events that preserve cardiac performance. Previous studies showed that halogenated anesthetics prime KATP channels under whole cell voltage clamp and act in intracellular pH (pHi)-dependent manner on KATP channels in excised membrane patches. However, it is not known how halogenated anesthetics interact with these channels. Methods The authors evaluated the effect of pHi and isoflurane on the KATP channel subunits, the pore-forming inward rectifier Kir6.2, and the regulatory sulfonylurea receptor SUR2A, using HEK293 cells as a heterologous expression system. Single channel activity was recorded in the inside-out patch configuration. Results At pHi 7.4, isoflurane had negligible effect on activity of wild-type Kir6.2/SUR2A, but at pHi 6.8, the channel open probability was increased by isoflurane (0.177 +/- 0.077 to 0.364 +/- 0.164). By contrast, the open probability of truncated Kir6.2DeltaC26, which forms a functional channel without SUR2A, was attenuated by isoflurane at both pHi 7.4 and pHi 6.8. Coexpression of Kir6.2DeltaC26 with SUR2A restored pHi sensitivity of channel activation by isoflurane. Site-directed mutagenesis within the Walker motifs of SUR2A abolished isoflurane activation of KATP channel at pHi 6.8. In addition, the pancreatic-type channels expressing sulfonylurea receptor SUR1 could not be activated by isoflurane. Conclusions The nucleotide binding domains of SUR2A play a crucial role in isoflurane facilitation of the KATP channel activity at moderately acidic pHi as would occur during early ischemia. These findings support direct and differential interaction of isoflurane with the subunits of the cardiac sarcolemmal KATP channel.

Differential Effects of Etomidate and Midazolam on Vascular Adenosine Triphosphate–sensitive Potassium Channels

2007 ◽  
Vol 106 (3) ◽  
pp. 515-522 ◽  
Author(s):  
Akiyo Nakamura ◽  
Shinji Kawahito ◽  
Takashi Kawano ◽  
Hossein Nazari ◽  
Akira Takahashi ◽  
...  
Keyword(s):  
Adenosine Triphosphate ◽  
Katp Channel ◽  
Amino Acid Level ◽  
Katp Channels ◽  
Rat Aorta ◽  
Isometric Tension ◽  
Sulfonylurea Receptor ◽  
Channel Activity ◽  
Inwardly Rectifying Potassium Channel ◽  
Ic50 Values

Background The aim of this study was to investigate the effects of two imidazoline-derived intravenous anesthetics, etomidate and midazolam, on vascular adenosine triphosphate-sensitive potassium (KATP) channel activity. Methods In isolated rat aorta, isometric tension was recorded to examine the anesthetic effects on vasodilator response to levcromakalim, a selective KATP channel opener. Using the patch clamp method, the anesthetic effects were also examined on the currents through (1) native vascular KATP channels, (2) recombinant KATP channels with different combinations of various types of inwardly rectifying potassium channel (Kir6.0 family: Kir6.1, 6.2) and sulfonylurea receptor (SUR1, 2A, 2B) subunits, (3) SUR-deficient channels derived from a truncated isoform of Kir6.2 subunit (Kir6.2DeltaC36 channels), and (4) mutant Kir6.2DeltaC36 channels with reduced sensitivity to adenosine triphosphate (Kir6.2DeltaC36-K185Q channels). Results Etomidate (> or = 10 m), but not midazolam (up to 10 m), inhibited the levcromakalim-induced vasodilation, which was sensitive to glibenclamide (IC50: 7.21 x 10 m; maximum inhibitory concentration: 1.22 x 10 m). Etomidate (> or = 3 x 10 m), but not midazolam (up to 10 m), inhibited the native KATP channel activity in both cell-attached and inside-out configurations with IC50 values of 1.68 x 10 m and 1.52 x 10 m, respectively. Etomidate (10 m) also inhibited the activity of various types of recombinant SUR/Kir6.0KATP channels, Kir6.2DeltaC36 channels, and Kir6.2DeltaC36-K185Q channels with equivalent potency. Conclusions Clinical concentrations of etomidate, but not midazolam, inhibit the KATP channel activity in vascular smooth muscle cells. The inhibition is presumably through its effects on the Kir6.0 subunit, but not on the SUR subunit, with the binding site different from adenosine triphosphate at the amino acid level.

Molecular Mechanisms of the Inhibitory Effects of Bupivacaine, Levobupivacaine, and Ropivacaine on Sarcolemmal Adenosine Triphosphate–sensitive Potassium Channels in the Cardiovascular System

2004 ◽  
Vol 101 (2) ◽  
pp. 390-398 ◽  
Author(s):  
Takashi Kawano ◽  
Shuzo Oshita ◽  
Akira Takahashi ◽  
Yasuo Tsutsumi ◽  
Yoshinobu Tomiyama ◽  
...  
Keyword(s):  
Cardiovascular System ◽  
Adenosine Triphosphate ◽  
Local Anesthetics ◽  
Molecular Mechanisms ◽  
Transmembrane Domain ◽  
Katp Channels ◽  
Inhibitory Effect ◽  
Amino Acid Residues ◽  
Sulfonylurea Receptor ◽  
Inhibitory Effects

Background Sarcolemmal adenosine triphosphate-sensitive potassium (KATP) channels in the cardiovascular system may be involved in bupivacaine-induced cardiovascular toxicity. The authors investigated the effects of local anesthetics on the activity of reconstituted KATP channels encoded by inwardly rectifying potassium channel (Kir6.0) and sulfonylurea receptor (SUR) subunits. Methods The authors used an inside-out patch clamp configuration to investigate the effects of bupivacaine, levobupivacaine, and ropivacaine on the activity of reconstituted KATP channels expressed in COS-7 cells and containing wild-type, mutant, or chimeric SURs. Results Bupivacaine inhibited the activities of cardiac KATP channels (IC50 = 52 microm) stereoselectively (levobupivacaine, IC50 = 168 microm; ropivacaine, IC50 = 249 microm). Local anesthetics also inhibited the activities of channels formed by the truncated isoform of Kir6.2 (Kir6.2 delta C36) stereoselectively. Mutations in the cytosolic end of the second transmembrane domain of Kir6.2 markedly decreased both the local anesthetics' affinity and stereoselectivity. The local anesthetics blocked cardiac KATP channels with approximately eightfold higher potency than vascular KATP channels; the potency depended on the SUR subtype. The 42 amino acid residues at the C-terminal tail of SUR2A, but not SUR1 or SUR2B, enhanced the inhibitory effect of bupivacaine on the Kir6.0 subunit. Conclusions Inhibitory effects of local anesthetics on KATP channels in the cardiovascular system are (1) stereoselective: bupivacaine was more potent than levobupivacaine and ropivacaine; and (2) tissue specific: local anesthetics blocked cardiac KATP channels more potently than vascular KATP channels, via the intracellular pore mouth of the Kir6.0 subunit and the 42 amino acids at the C-terminal tail of the SUR2A subunit, respectively.

scholarly journals The Role of PKM2 in Metabolic Reprogramming: Insights into the Regulatory Roles of Non-Coding RNAs

2021 ◽  
Vol 22 (3) ◽  
pp. 1171
Author(s):  
Dexter L. Puckett ◽  
Mohammed Alquraishi ◽  
Winyoo Chowanadisai ◽  
Ahmed Bettaieb
Keyword(s):  
Cancer Cells ◽  
Pyruvate Kinase ◽  
Cancer Metabolism ◽  
Cell Metabolism ◽  
Metabolic Reprogramming ◽  
Circular Rnas ◽  
Tissue Specific ◽  
Cell Progression ◽  
Non Coding Rnas ◽  
Regulatory Effects

Pyruvate kinase is a key regulator in glycolysis through the conversion of phosphoenolpyruvate (PEP) into pyruvate. Pyruvate kinase exists in various isoforms that can exhibit diverse biological functions and outcomes. The pyruvate kinase isoenzyme type M2 (PKM2) controls cell progression and survival through the regulation of key signaling pathways. In cancer cells, the dimer form of PKM2 predominates and plays an integral role in cancer metabolism. This predominance of the inactive dimeric form promotes the accumulation of phosphometabolites, allowing cancer cells to engage in high levels of synthetic processing to enhance their proliferative capacity. PKM2 has been recognized for its role in regulating gene expression and transcription factors critical for health and disease. This role enables PKM2 to exert profound regulatory effects that promote cancer cell metabolism, proliferation, and migration. In addition to its role in cancer, PKM2 regulates aspects essential to cellular homeostasis in non-cancer tissues and, in some cases, promotes tissue-specific pathways in health and diseases. In pursuit of understanding the diverse tissue-specific roles of PKM2, investigations targeting tissues such as the kidney, liver, adipose, and pancreas have been conducted. Findings from these studies enhance our understanding of PKM2 functions in various diseases beyond cancer. Therefore, there is substantial interest in PKM2 modulation as a potential therapeutic target for the treatment of multiple conditions. Indeed, a vast plethora of research has focused on identifying therapeutic strategies for targeting PKM2. Recently, targeting PKM2 through its regulatory microRNAs, long non-coding RNAs (lncRNAs), and circular RNAs (circRNAs) has gathered increasing interest. Thus, the goal of this review is to highlight recent advancements in PKM2 research, with a focus on PKM2 regulatory microRNAs and lncRNAs and their subsequent physiological significance.

Characterization of ATP-sensitive potassium channels in freshly dissociated rabbit aortic endothelial cells

1997 ◽  
Vol 272 (5) ◽  
pp. H2507-H2511 ◽  
Author(s):  
C. Katnik ◽  
D. J. Adams
Keyword(s):  
Endothelial Cells ◽  
Single Channel ◽  
Muscle Tone ◽  
Cell Metabolism ◽  
Katp Channels ◽  
K Channel ◽  
Membrane Hyperpolarization ◽  
Aortic Endothelial Cells ◽  
Intracellular Atp ◽  
Aortic Endothelial

ATP-sensitive potassium (KATP) channels represent a class of K+ channel regulated by intracellular ATP and serve to transduce changes in cell metabolism into changes in membrane potential. The presence of an KATP conductance has recently been demonstrated in freshly dissociated endothelial cells from rabbit arteries. In the present study, the single-channel activity underlying the KATP conductance in rabbit aortic endothelial cells was examined. Unitary currents were evoked in response to lowering intracellular ATP concentration or application of the K(+)-channel activator levcromakalim and were inhibited by the sulfonylurea drug glibenclamide. Exposure of the cytoplasmic face of an inside-out membrane patch to a solution containing 0.1 mM ATP produced single-channel events with unitary conductances of approximately 150 and approximately 25 pS that were inhibited by either 6 mM ATP or 10 microM glibenclamide. A small conductance channel was also activated in cell-attached patches by bath-applied levcromakalim (25 microM). Activation of endothelial cell KATP channels, and subsequent membrane hyperpolarization, may contribute to endothelium-dependent regulation of vascular smooth muscle tone in response to changes in levels of intracellular metabolites.

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