title: Adenosine Triphosphate-Sensitive Potassium Channel Kir Subunits Implicated in Cardioprotection by Diazoxide.
abstract: BACKGROUND
  ATP-sensitive potassium (K(ATP)) channel openers provide cardioprotection in multiple models. Ion flux at an unidentified mitochondrial K(ATP) channel has been proposed as the mechanism. The renal outer medullary kidney potassium channel subunit, potassium inward rectifying (Kir)1.1, has been implicated as a mitochondrial channel pore-forming subunit. We hypothesized that subunit Kir1.1 is involved in cardioprotection (maintenance of volume homeostasis and contractility) of the K(ATP) channel opener diazoxide (DZX) during stress (exposure to hyperkalemic cardioplegia [CPG]) at the myocyte and mitochondrial levels.
  
  
  RESULTS
  Kir subunit inhibitor Tertiapin Q (TPN-Q) was utilized to evaluate response to stress. Mouse ventricular mitochondrial volume was measured in the following groups: isolation buffer; 200 μmol/L of ATP; 100 μmol/L of DZX+200 μmol/L of ATP; or 100 μmol/L of DZX+200 μmol/L of ATP+TPN-Q (500 or 100 nmol/L). Myocytes were exposed to Tyrode's solution (5 minutes), test solution (Tyrode's, cardioplegia [CPG], CPG+DZX, CPG+DZX+TPN-Q, Tyrode's+TPN-Q, or CPG+TPN-Q), N=12 for all (10 minutes); followed by Tyrode's (5 minutes). Volumes were compared. TPN-Q, with or without DZX, did not alter mitochondrial or myocyte volume. Stress (CPG) resulted in myocyte swelling and reduced contractility that was prevented by DZX. TPN-Q prevented the cardioprotection afforded by DZX (volume homeostasis and maintenance of contractility).
  
  
  CONCLUSIONS
  TPN-Q inhibited myocyte cardioprotection provided by DZX during stress; however, it did not alter mitochondrial volume. Because TPN-Q inhibits Kir1.1, Kir3.1, and Kir3.4, these data support that any of these Kir subunits could be involved in the cardioprotection afforded by diazoxide. However, these data suggest that mitochondrial swelling by diazoxide does not involve Kir1.1, 3.1, or 3.4.
authors: Division of Cardiothoracic Surgery, Department of Surgery, Washington University School of Medicine, St. Louis, MO (M.C.H., B.J., E.M.K., C.M.M., R.B.S., J.S.L.).
authors: Matthew C
authors: MC
authors: Henn
authors: Division of Cardiothoracic Surgery, Department of Surgery, Washington University School of Medicine, St. Louis, MO (M.C.H., B.J., E.M.K., C.M.M., R.B.S., J.S.L.).
authors: M Burhan
authors: MB
authors: Janjua
authors: Division of Cardiothoracic Surgery, Department of Surgery, Washington University School of Medicine, St. Louis, MO (M.C.H., B.J., E.M.K., C.M.M., R.B.S., J.S.L.).
authors: Evelyn M
authors: EM
authors: Kanter
authors: Division of Cardiothoracic Surgery, Department of Surgery, Washington University School of Medicine, St. Louis, MO (M.C.H., B.J., E.M.K., C.M.M., R.B.S., J.S.L.).
authors: Carol M
authors: CM
authors: Makepeace
authors: Division of Cardiothoracic Surgery, Department of Surgery, Washington University School of Medicine, St. Louis, MO (M.C.H., B.J., E.M.K., C.M.M., R.B.S., J.S.L.).
authors: Richard B
authors: RB
authors: Schuessler
authors: Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO (C.G.N.).
authors: Colin G
authors: CG
authors: Nichols
authors: Division of Cardiothoracic Surgery, Department of Surgery, Washington University School of Medicine, St. Louis, MO (M.C.H., B.J., E.M.K., C.M.M., R.B.S., J.S.L.).
authors: Jennifer S
authors: JS
authors: Lawton
mesh_terms: D000818:Animals; D003981:Diazoxide / Q000494:pharmacology*; D005260:Female; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels / Q000819:agonists / Q000378:metabolism; D006324:Heart Arrest, Induced; D008297:Male; D049990:Membrane Transport Modulators / Q000494:pharmacology*; D008810:Mice, Inbred C57BL; D008929:Mitochondria, Heart / Q000187:drug effects* / Q000378:metabolism; D053142:Mitochondrial Size / Q000187:drug effects; D009200:Myocardial Contraction / Q000187:drug effects; D032383:Myocytes, Cardiac / Q000187:drug effects* / Q000378:metabolism; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000819:agonists* / Q000378:metabolism; D024661:Potassium Channels, Inwardly Rectifying / Q000819:agonists* / Q000378:metabolism; D013312:Stress, Physiological; D013997:Time Factors
chemical_list: D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; C510693:Kcnj1 protein, mouse; C497067:Kcnj3 protein, mouse; C484273:Kcnj5 protein, mouse; D049990:Membrane Transport Modulators; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; C117780:mitochondrial K(ATP) channel; D003981:Diazoxide
keywords: cardioplegia; ion channels; myocardial stunning; potassium