1. Cardioprotective Mechanism of Diazoxide Involves the Inhibition of Succinate Dehydrogenase 
Melissa M. Anastacio, MD, Evelyn M. Kanter, BS, Carol Makepeace, BS, Angela D. Keith, MS, Haixia Zhang, PhD, Richard B. Schuessler, PhD, Colin G. Nichols, PhD, Jennifer S. Lawton, MD 
The Annals of Thoracic Surgery 
Volume 95, Issue 6, Pages (June 2013)
DOI: /j.athoracsur
Copyright © 2013 The Society of Thoracic Surgeons Terms and Conditions

2. Fig 1
Representation of the adenosine triphosphate-sensitive potassium channel (KATP) and the succinate dehydrogenase (SDH) enzyme complex on the inner mitochondrial membrane. Adenosine triphosphate-sensitive potassium channel opener diazoxide provides myocyte volume homeostasis and preserves contractility during stress via an unknown mechanism. Diazoxide also inhibits SDH. The relationship between the KATP channel activity and SDH during stress is unknown. Glutathione was utilized to determine the role of inhibition of SDH in diazoxide’s cardioprotection. Mitochondria from our laboratory visualized through electron microscopy (mag 3,000×). (KATP channel figure partially reproduced with permission from Sellitto and colleagues [8], and SDH image from en.wikipedia.org.) (C = C terminus; Kir = potassium inward rectifying; N = N terminus; NBF = nucleotide binding fold; SUR = sulfonylurea receptor subunit; TM = transmembrane; TMD = transmembrane domain.)
The Annals of Thoracic Surgery  , DOI: ( /j.athoracsur )
Copyright © 2013 The Society of Thoracic Surgeons Terms and Conditions

3. Fig 2
Diazoxide (DZX) inhibits succinate dehydrogenase (SDH) activity. Isolated mitochondria were exposed to test solutions for 20 minutes. The SDH activity is represented as percent change in absorbance over time. The SDH activity is inversely proportional to absorbance. The 10 μM glutathione did not prevent inhibition of SDH by DZX.
The Annals of Thoracic Surgery  , DOI: ( /j.athoracsur )
Copyright © 2013 The Society of Thoracic Surgeons Terms and Conditions

4. Fig 3
Glutathione (GLU; 25 μM) prevents diazoxide (DZX) inhibition of succinate dehydrogenase (SDH). Isolated mitochondria were exposed to test solutions for 20 minutes. The SDH activity is represented as percent change in absorbance over time. The SDH activity is inversely proportional to absorbance. The addition of 25 μM GLU prevented the inhibition of SDH by DZX.
The Annals of Thoracic Surgery  , DOI: ( /j.athoracsur )
Copyright © 2013 The Society of Thoracic Surgeons Terms and Conditions

5. Fig 4
Glutathione (100 μM) prevents diazoxide’s (DZX) inhibition of succinate dehydrogenase (SDH). Isolated mitochondria were exposed to test solutions for 20 minutes. The SDH activity is represented as percent change in absorbance over time. The SDH activity is inversely proportional to absorbance. The addition of 100 μM glutathione prevented the inhibition of SDH activity by DZX.
The Annals of Thoracic Surgery  , DOI: ( /j.athoracsur )
Copyright © 2013 The Society of Thoracic Surgeons Terms and Conditions

6. Fig 5
Glutathione’s (GLU) ability to prevent the inhibition of succinate dehydrogenase (SDH) by diazoxide (DZX) is dose dependent. Isolated mitochondria were exposed to test solutions for 20 minutes. The SDH activity is represented as percent change in absorbance over time. The SDH activity is inversely proportional to absorbance.
The Annals of Thoracic Surgery  , DOI: ( /j.athoracsur )
Copyright © 2013 The Society of Thoracic Surgeons Terms and Conditions

7. Fig 6
Glutathione (GLU) prevented volume homeostasis provided by diazoxide (DZX) during stress. Isolated myocytes were exposed to Tyrode’s during time 0 to 20 minutes, test solutions during time 20 to 40 minutes, and Tyrode’s during time 40 to 60 minutes. Stress in the form of hyperkalemic cardioplegia (CPG) resulted in significant myocyte swelling that was prevented by DZX. The GLU prevented the beneficial effect noted with DZX during myocyte stress.
The Annals of Thoracic Surgery  , DOI: ( /j.athoracsur )
Copyright © 2013 The Society of Thoracic Surgeons Terms and Conditions

8. Fig 7
Glutathione (GLU) improved myocyte contractility after re-exposure to Tyrode’s. (A) Myocyte contractility at 10 minutes after re-exposure to Tyrode’s. Isolated myocytes were exposed to Tyrode’s during time 0 to 20 minutes, test solutions during time 20 to 40 minutes, and Tyrode’s during time 40 to 60 minutes. The GLU was associated with an improvement in contractility with or without myocyte stress. (B) Myocyte contractility at 20 minutes after re-exposure to Tyrode’s. Isolated myocytes were exposed to Tyrode’s physiologic solution during time 0 to 20 minutes, test solutions during time 20 to 40 minutes, and Tyrode’s during time 40 to 60 minutes. Glutathione was associated with an improvement in contractility with or without myocyte stress. (CPG = cardioplegia; DZX = diazoxide.)
The Annals of Thoracic Surgery  , DOI: ( /j.athoracsur )
Copyright © 2013 The Society of Thoracic Surgeons Terms and Conditions