Download - Pravdić D. 1,3 , Aggarwal N. 2 , Mcnally M. E. 4 , Bošnjak Ž. 3 , Nian-Qing Shi 2 , Makielski J. 2
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Disruption of sulfonylurea receptor-2 protects against ischemia and
reperfusion injury via modulation of mitochondrial bioenergetic phenotype
Pravdić D.1,3, Aggarwal N.2, Mcnally M. E.4, Bošnjak Ž.3, Nian-Qing Shi2, Makielski J.2
Mostar School of Medicine, Mostar, BIH 1
University of Wisconsin, Madison, Madison, WI, USA 2
Medical College of Wisconsin, Milwaukee, WI, USA 3
University of Chicago, Chicago, IL, USA 4
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• First discovered in the heart by Noma (Nature 1983; 305: 147-8).
• “An outward current of unknown nature increases significantly when cardiac cells are treated with cyanide or subjected to hypoxia, and decreases on intracellular injection of ATP.”
• ATP-regulated K+ channels
KATP Channels
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• Following studies identified KATP channels in
other tissues:
• Pancreatic β-cells
• Vascular smooth muscle
• Skeletal muscle
• Brain
• Kidney
• etc.
KATP Channels
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Cardiac sarcKATP Channels
• Under normal metabolic conditions closed.
• During metabolic stress they open - cellular metabolic sensors.
SUR2A Kir6.2
COO-
NH2
ATP ADPH+
-+
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Cardiac KATP Channels
Mitochondrial KATP channel
K+
K+
K+
K+
Sarcolemmal KATP
channel
K+ K+K+ K+
K+
K+
K+
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The Mechanism of Protection
Ca2+
Extracellular
K+
SarcKATP Channel
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MitoKATP channels and cellular protection
• MitoKATP channel activator
diazoxide reduced the
severity of ischemia/
reperfusion damage in rat
hearts (Garlid et al., Circ Res
1997;81:1072-82)Fig. 4
Vehicle Diazo Diazo+5-HD
• Diazoxide protected rabbit
cardiomyocytes from ischemia
in a 5-HD dependent manner (Liu et al., Circulation 1998;97:2463-9)
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• Suppression of mitochondrial Ca2+ overload
Proposed mechanisms of protection
ΔΨm -200 mV ΔΨm depolarized
Ca2+ Ca2+
Mitochondrial K+ channels openCa2+ Ca2+
K+
• Mitochondrial swelling and improved oxidative phosphorylation
ATPMitochondrial K+ channels open
H+ A-
Pi-
K+
K+
OH-
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• Freshly isolated cardiac myocytes
– Effect on mitochondrial membrane potential (ΔΨm)
• Isolated cardiac mitochondria
– Mitochondrial bioenergetics
– Ca2+ loading
– Resistance to stress
Experimental Design
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Animals
• A transgenic mouse was created previously (SUR2 mutant) where the gene encoding SUR2 was disrupted by removing exons 14 to 18 encoding the first nucleotide binding domain.
• These SUR2 mutant mice lack pinacidil, diazoxide and glybenclamide sensitive sarcKATP currents in the cardiac, smooth and skeletal muscle and they are hypertensive, arrhythmic, and exhibit coronary vasospasm and sudden cardiac death
• SUR2 mutant mice have increased protection against both acute adrenergic stress and ischemia compared to control
Stoller D, Kakkar R, Smelley M, Chalupsky K, Earley JU, Shi NQ, Makielski JC, McNally EM.
Mice lacking sulfonylurea receptor 2 (SUR2) ATP-sensitive potassium channels
are resistant to acute cardiovascular stress. J Mol Cell Cardiol. 2007;43:445-454.
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Mitochondrial membrane potential
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Mitochondrial swelling
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Resistance to Ca2+ loading
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Effect of hypoxia-reoxygenation on mitochondrial respiration
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Myocite Resistance to metabolic inhibition
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Conclusions
• SUR2 mutant mitochondria had more depolarized ΔΨm compared to wild type
• Tolerance to Ca2+ loading was increased in SUR2 mutant mitochondria
• Mitochondria swelling, an indicator of K+ influx, was greater in SUR2 mutants
• SUR2 mutant mitochondria recovered better from hypoxia-reoxygenation injury than Wild type
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Acknowledgements
Zeljko J. Bosnjak, PhD
Nitin Aggarwal, PhD
Martin Bienengraeber, PhD
Jonatan Makielski, MD
Elizabeth McNally, MD
Chiaki Kwok