AJP - Heart Fuel your research with LabChart
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

Am J Physiol Heart Circ Physiol 291: H2041-H2043, 2006. First published July 28, 2006; doi:10.1152/ajpheart.00772.2006
0363-6135/06 $8.00
This Article
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
291/5/H2041    most recent
00772.2006v1
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via ISI Web of Science (2)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Kukreja, R. C.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Kukreja, R. C.

EDITORIAL FOCUS

Mechanism of reactive oxygen species generation after opening of mitochondrial KATP channels

Rakesh C. Kukreja

Department of Internal Medicine, Division of Cardiology, Virginia Commonwealth University Medical Center, Richmond, Virginia

OPENING of the ATP-sensitive K+ (KATP) channel mediates the cardioprotective effect induced by pathophysiological stressors such as ischemic preconditioning (IPC) (15, 29), heat shock (19), and pharmacological agents, including adenosine (5), ACh (26), opioids (12), monophosphoryl lipid A (31), phosphodiesterase 5A (PDE5A) inhibitors (24, 27), and mTOR inhibitor, rapamycin (20). In addition, direct opening of the mitochondrial KATP (mitoKATP) channels with diazoxide induces early and delayed preconditioning effects that are abolished by the channel inhibitor 5-hydroxydecanoate (5-HD) (23). The mitoKATP channels are activated when intracellular ATP levels drop. Within 1–3 min of ischemia, there is a pronounced shortening of the action potential duration (APD) secondary to activation of the KATP channels (6). Activation of KATP channels has been reported to be partially responsible for the increase in outward K+ currents, shortening of APD, and the increase in extracellular K+ concentration during anoxic or globally ischemic conditions (4). Because there was a lack of correlation between the APD shortening and cardioprotection with the pharmacological openers of KATP channels (17), Garlid et al. (14) first proposed that mitoKATP channels were involved in the cardioprotective effect. By using reconstituted mitochondrial vesicles or isolated mitochondria and measuring potassium flux, these investigators demonstrated that heart and liver mitoKATP channels shared pharmacological properties with the channels found in sarcolemma while possessing a distinct profile. Furthermore, it was shown that opening of mitoKATP channels leads to the generation of reactive oxygen species (ROS) by the mitochondria and represents an important mechanism that is required for the cardioprotective effect of IPC (25, 30). Opening of these channels allowed potassium to enter the mitochondrial inner matrix, which causes generation and release of ROS from the respiratory chain (21). ROS then act as second messengers to activate a downstream pathway of protective kinases, including protein kinase C (PKC), that finally converge on the cardioprotective end effector as shown in Fig. 1. One of the principal downstream effectors of ROS is PKC{epsilon} (2), which is translocated to the mitochondria (3). Cardioprotection conferred by IPC and pharmacological agents is blocked by ROS scavengers before the index ischemia (11, 25). In most earlier studies, mitoKATP channels were proposed to be end effectors, and the channels were assumed to open during the index ischemia (13, 15). Recent studies, however, suggest that opening of mitoKATP channels is also the initial trigger of the cardioprotective effect, promoting the generation of ROS and inducing the activation of PKC{epsilon} (11, 25). Other studies have suggested that mitoKATP channels act both as a trigger as well as an end effector of IPC (16). In contrast to these studies, Hanley and coworkers (10) recently challenged that diazoxide does not evoke superoxide (which dismutates to H2O2) from the respiratory chain by a direct mechanism. They reported that the stimulatory effects of this compound on mitochondrial respiration and oxidation of dichlorodihydrofluorescein (fluorescent probe for ROS) is not due to the opening of mitoKATP channels. Moreover, these authors suggested that inhibitory effect of decanoate on diazoxide-induced flavoprotein oxidation supports the notion that 5-HD acts as a metabolic substrate rather than a mitoKATP channel inhibitor. Clearly, there are controversial issues that need to be resolved in the future.


Figure 1
View larger version (13K):
[in this window]
[in a new window]
  		Fig. 1. Flow diagram showing the signal transduction steps that lead to cardioprotection after ischemic and pharmacological preconditioning. See text for a detailed explanation. PED5A, phosphodiesterase 5A; PKG, protein kinase G; ROS, reactive oxygen species.

 
There has also been considerable interest in the role of the nitric oxide (NO)-cGMP-protein kinase G (PKG)-pathway in protection of the heart against ischemia-reperfusion injury (18). PKG is a serine/threonine protein kinase and is one of the major intracellular receptors for cGMP. Inhibition of cGMP-specific PDE5A with selective potent inhibitors, sildenafil citrate (Viagra) and vardenafil (Levitra), induced protective effects against ischemia-reperfusion injury in the intact heart (24, 28) and adult cardiomyocytes (9). Conceptually, these drugs inhibit the enzymatic hydrolysis of cGMP, which in turn maintains the tissue accumulation of cGMP, leading to downstream protective mechanisms involving activation of PKG and opening of mitoKATP channels. Our studies showed that sildenafil induces IPC through NO generated from endothelial and/or inducible nitric oxide synthase, activation of PKC, and opening of the mitoKATP channels (reviewed in Ref. 22). Similarly, bradykinin mimics IPC by generating ROS, and it does so via cGMP activation of PKG (8). Furthermore, Costa et al. showed that PKG + cGMP induce mitoKATP channel opening via an endogenous PKC-{epsilon} in isolated mitochondria (7).

It is quite obvious from the above review that there is overwhelming evidence for the involvement of ROS in cardioprotection. However, there is no direct demonstration that mitoKATP channel opening actually leads to ROS production in the mitochondria. Moreover, the mechanism and the site of ROS generation are unknown. What Garlid and associates (1) have proposed in this issue of the American Journal of Physiology-Heart and Circulatory Physiology is a novel mechanism of ROS generation with the opening of mitoKATP channel. By using a series of fluorescent probes that are sensitive to hydrogen peroxide and pH, they measured their changes in suspensions of isolated rat heart and liver mitochondria. The data suggest that the K+-specific ionophore valinomycin quantitatively reproduced the ROS production similar to that observed by the mitoKATP openers diazoxide and chromakalim. They further show that alkaline pH but not increasing the matrix volume by itself enhanced ROS production. These results are supported by carefully and systematically presented data. Neutralization of the matrix pH with acetic acid led to the blockade of the stimulatory effect of valinomycin on ROS production. Furthermore, ROS production exhibited a biphasic dependence on valinomycin concentration, with peak production occurring at valinomycin concentrations that catalyze about the same K+ influx as mitoKATP channel openers. The ROS production decreased with higher concentrations of valinomycin and with all concentrations of a classical protonophoretic uncoupler. These data suggest that the increase in ROS is due specifically to K+ influx into the matrix and is mediated by the attendant matrix alkalinization. The authors went on to demonstrate the applicability of this mechanism with PKG + cGMP and the PKC activator PMA in the isolated mitochondria. Using isoform specific blockers, they show that PKG + cGMP and PMA stimulate mitochondrial ROS production in a PKC{epsilon}-dependent and mitoKATP-dependent manner. The authors propose that electrons are passed to ubiquinone from complex I (NADH:ubiquinone oxidoreductase) of the electron transport chain. The increase of matrix pH causes retardation of the electron flow at the FMNH2 or FMN semiquinone sites. This results in the increase in reduction at the flavin site and consequent increase in steady-state superoxide production.

Overall, this study offers a provocative mechanism by which ROS are generated with the opening of the mitoKATP either directly with the use of pharmacological openers or signaling pathway(s) involving activation of PKG and PKC. Obviously, one of the limitations of this study is that it was performed in vitro in the isolated heart and liver mitochondrial preparations. Therefore, it is far too soon to make predictions of the relevance of these findings in explaining the mechanism of ROS generation in vivo with the cardioprotective modalities, including ischemic and pharmacological preconditioning. Clearly, future investigations are needed to address this important issue.

GRANTS

The study was supported in part by National Heart, Lung, and Blood Institute Grants HL-51045, HL-59469, and HL-79424.

FOOTNOTES


Address for reprint requests and other correspondence: R. C. Kukreja, Dept. of Medicine, Physiology, Biochemistry, and Emergency Medicine, Eric Lipman Chair of Cardiology, Virginia Commonwealth Univ. Medical Center, Richmond, VA 23298 (e-mail: rakesh{at}hsc.vcu.edu)

REFERENCES

  1. Andrukhiv A, Costa AD, West IC, and Garlid KD. Opening mitoKATP increases superoxide generation from complex I of the electron transport chain. Am J Physiol Heart Circ Physiol 291: H2067–H2074, 2006.[Abstract/Free Full Text]
  2. Baines CP, Zhang J, Wang GW, Zheng Y-T, Xiu JX, Cardwell EM, Bolli R, and Ping P. Mitochondrial PKC{epsilon} and MAPK form signaling modules in the murine heart: enhanced mitochondrial PKC{epsilon}-MAPK interactions and differential MAPK activation in PKC{epsilon}-induced cardioprotection Circ Res 90, 390–397, 2002.[Abstract/Free Full Text]
  3. Baines CP, Song CX, Zheng YT, Wang GW, Zhang J, Wang OL, Guo Y, Bolli R, Cardwell EM, and Ping P. Protein kinase C{epsilon} interacts with and inhibits the permeability transition pore in cardiac mitochondria. Circ Res 92: 873–880, 2003.[Abstract/Free Full Text]
  4. Bekheit SS, Restivo M, Boutjdir M, Henkin R, Gooyandeh K, Assadi M, Khatib S, Gough WB, and el-Sherif N. Effects of glyburide on ischemia-induced changes in extracellular potassium and local myocardial activation: a potential new approach to the management of ischemia-induced malignant ventricular arrhythmias. Am Heart J 119: 1025–1033, 1990.[CrossRef][ISI][Medline]
  5. Bernardo NL, Okubo S, Maaieh M, Wood MA, and Kukreja RC. Delayed preconditioning with adenosine is mediated by opening of ATP-sensitive K+ channels in rabbit heart. Am J Physiol Heart Circ Physiol 277: H128–H135, 1999.[Abstract/Free Full Text]
  6. Cole WC, McPherson CD, and Sontag D. ATP-regulated K+ channels protect the myocardium against ischemia/reperfusion damage. Circ Res 69: 571–581, 1991.[Abstract/Free Full Text]
  7. Costa AD, Garlid KD, West IC, Lincoln TM, Downey JM, Cohen MV, and Critz SD. Protein kinase G transmits the cardioprotective signal from cytosol to mitochondria. Circ Res 97: 329–336, 2005.[Abstract/Free Full Text]
  8. Critz SD, Cohen MV, and Downey JM. Mechanisms of acetylcholine- and bradykinin-induced preconditioning. Vascul Pharmacol 42: 201–209, 2005.[CrossRef][ISI][Medline]
  9. Das A, Xi L, and Kukreja RC. Phosphodiesterase-5 inhibitor sildenafil preconditions adult cardiac myocytes against necrosis and apoptosis. Essential role of nitric oxide signaling. J Biol Chem 280: 12944–12955, 2005.[Abstract/Free Full Text]
  10. Drose S, Brandt U, and Hanley PJ. K+-independent actions of diazoxide question the role of inner membrane KATP channels in mitochondrial cytoprotective signaling. J Biol Chem 281: 23733–23739, 2006.[Abstract/Free Full Text]
  11. Forbes RA, Steenbergen C, and Murphy E. Diazoxide-induced cardioprotection requires signaling through a redox-sensitive mechanism. Circ Res 88: 802–809, 2001.[Abstract/Free Full Text]
  12. Fryer RM, Hsu AK, Eells JT, Nagase H, and Gross GJ. Opioid-induced second window of cardioprotection: potential role of mitochondrial KATP channels. Circ Res 84: 846–851, 1999.[Abstract/Free Full Text]
  13. Fryer RM, Hsu AK, and Gross GJ. Mitochondrial KATP channel opening is important during index ischemia and following myocardial reperfusion in ischemic preconditioned rat hearts. J Mol Cell Cardiol 33: 831–834, 2001.[CrossRef][ISI][Medline]
  14. Garlid KD, Paucek P, Yarov-Yarovoy V, Murray HN, Darbenzio RB, D'Alonzo AJ, Lodge NJ, Smith MA, and Grover GJ. Cardioprotective effect of diazoxide and its interaction with mitochondrial ATP-sensitive K+ channels. Possible mechanism of cardioprotection. Circ Res 81: 1072–1082, 1997.[Abstract/Free Full Text]
  15. Gross GJ and Auchampach JA. Blockade of ATP-sensitive potassium channels prevents myocardial preconditioning in dogs. Circ Res 70: 223–233, 1992.[Abstract/Free Full Text]
  16. Gross GJ and Peart JN. KATP channels and myocardial preconditioning: an update. Am J Physiol Heart Circ Physiol 285: H921–H930, 2003.[Abstract/Free Full Text]
  17. Grover GJ, Dalonzo AJ, Parham CS, and Darbenzio RB. Cardioprotection with the KATP opener is not correlated with ischemic myocardial action potential duration. J Cardiovasc Pharmacol 26: 145–152, 1995.[ISI][Medline]
  18. Han J, Kim N, Kim E, Ho WE, and Earm YE. Modulation of ATP-sensitive potassium channels by cGMP-dependent protein kinase in rabbit ventricular myocytes. J Biol Chem 276: 22140–22147, 2001.[Abstract/Free Full Text]
  19. Hoag JB, Qian YZ, Nayeem MA, D'Angelo M, and Kukreja RC. ATP-sensitive potassium channel mediates delayed ischemic protection by heat stress in rabbit heart. Am J Physiol Heart Circ Physiol 273: H861–H868, 1997.[Abstract/Free Full Text]
  20. Khan SA, Salloum F, Das A, Xi L, Vetrovec GW, and Kukreja RC. Rapamycin confers preconditioning-like protection against ischemia-reperfusion injury in isolated mouse heart and cardiomyocytes. J Mol Cell Cardiol. In Press.
  21. Krenz M, Oldenburg O, Wimpee H, Cohen MV, Garlid KD, Critz SD, Downey JM, and Benoit JN. Opening of ATP-sensitive potassium channels causes generation of free radicals in vascular smooth muscle cells. Basic Res Cardiol 97: 365–373, 2002.[CrossRef][ISI][Medline]
  22. Kukreja RC, Ockaili R, Salloum F, Yin C, Hawkins, J, Das A, and Xi L. Cardioprotection with phosphodiesterase-5 inhibition—a novel preconditioning strategy. J Mol Cell Cardiol 36: 165–173, 2004.[CrossRef][ISI][Medline]
  23. Ockaili R, Emani VR, Okubo S, Brown M, Krottapalli K, and Kukreja RC. Opening of mitochondrial KATP channel induces early and delayed cardioprotective effect: role of nitric oxide. Am J Physiol Heart Circ Physiol 277: H2425–H2434, 1999.[Abstract/Free Full Text]
  24. Ockaili R, Salloum F, Hawkins J, and Kukreja RC. Sildenafil (Viagra) induces powerful cardioprotective effect via opening of mitochondrial KATP channels in rabbits. Am J Physiol Heart Circ Physiol 283: H1263–H1269, 2002.[Abstract/Free Full Text]
  25. Pain T, Yang XM, Critz SD, Yue Y, Nakano A, Liu GS, Heusch G, Cohen MV, and Downey JM. Opening of mitochondrial KATP channels triggers the preconditioned state by generating free radicals. Circ Res 87: 460–466, 2000.[Abstract/Free Full Text]
  26. Qian YZ, Levasseur JE, Yoshida KI, and Kukreja RC. KATP channels in rat heart: blockade of ischemic and acetylcholine-mediated preconditioning by glibenclamide. Am J Physiol Heart Circ Physiol 271: H23–H28, 1996.[Abstract/Free Full Text]
  27. Salloum FN, Ockaili RA, Wittkamp M, Marwaha VR, and Kukreja RC. Vardenafil: a novel type 5 phosphodiesterase inhibitor reduces myocardial infarct size following ischemia/reperfusion injury via opening of mitochondrial KATP channels in rabbits. J Mol Cell Cardiol 40: 405–411, 2006.[CrossRef][ISI][Medline]
  28. Salloum F, Yin C, Xi L, and Kukreja RC. Sildenafil induces delayed preconditioning through inducible nitric oxide synthase-dependent pathway in mouse heart. Circ Res 92: 595–597, 2003.[Abstract/Free Full Text]
  29. Schultz JEJ, Qian YZ, Gross GJ, and Kukreja RC. Specific ATP-sensitive potassium channel antagonist 5-hydroxydecanoate blocks ischemic preconditioning in the rat heart. J Mol Cell Cardiol 29: 1055–1060, 1997.[CrossRef][ISI][Medline]
  30. Vanden Hoek TL, Becker LB, Shao Z, Li C, and Schumacker PT. Reactive oxygen species released from mitochondria during brief hypoxia induce preconditioning in cardiomyocytes. J Biol Chem 273: 18092–18098, 1998.[Abstract/Free Full Text]
  31. Yoshida KI, Maaieh MM, Shipley JB, Doloresco M, Bernardo NL, Qian YZ, Elliott GT, and Kukreja RC. Monophosphoryl lipid A induces pharmacologic "preconditioning" in rabbit hearts without concomitant expression of 70-kDa heat shock protein. Mol Cell Biochem 159: 73–80, 1996.[ISI][Medline]



This article has been cited by other articles:


Home page
 J. Appl. Physiol.Home page
A. Jahangir, S. Sagar, and A. Terzic
Aging and cardioprotection
J Appl Physiol, December 1, 2007; 103(6): 2120 - 2128.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
291/5/H2041    most recent
00772.2006v1
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via ISI Web of Science (2)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Kukreja, R. C.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Kukreja, R. C.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
Visit Other APS Journals Online
Copyright © 2006 by the American Physiological Society.