Mitochondrial potassium ATP channels and retinal ischemic preconditioning.
OBJECTIVE
To examine the mechanisms of ischemic preconditioning (IPC) related to the opening of mitochondrial KATP (mKATP) channels in the retina.


METHODS
Rats were subjected to retinal ischemia after IPC, or retinas were rendered ischemic after pharmacological opening of mKATP channels. The effects of blocking mKATP channel opening, nitric oxide synthase (NOS) subtypes, or protein kinase C (PKC) on the protective effect of IPC or on the opening of mKATP channels were studied. Electroretinography assessed functional recovery after ischemia. Immunohistochemistry and image analysis were used to measure changes in levels of reactive oxygen species (ROS) and NOS subtypes and to determine their cellular localization.


RESULTS
IPC was effectively mimicked by injection of the mKATP channel opener diazoxide. Both IPC and its mimicking by diazoxide were completely attenuated by the mKATP channel blocker 5-hydroxydecanoic acid (5-HD). Nonspecific blockade of NOS by N(omega)-nitro-L-arginine (L-NNA), but not by specific inducible (i)NOS or neuronal (n)NOS inhibitors, blunted IPC and IPC-mimicking, as did blockade of PKC. IPC and diazoxide IPC-mimicking significantly enhanced mitochondrial ROS production in the inner retina, an effect blocked by 5-HD. Mitochondrial ROS colocalized with e- and nNOS in retinal cells after stimulation with diazoxide.


CONCLUSIONS
The results showed that IPC in the retina requires opening of the mKATP channel, and that IPC could be effectively mimicked using the mKATP channel opener diazoxide. eNOS-generated nitric oxide, PKC, and ROS are activated by opening of the mKATP channel.
Roth
Steven
S
Department of Anesthesia and Critical Care, University of Chicago, Illinois 60637, USA. sroth@dacc.uchicago.edu
Dreixler
John C
JC
Shaikh
Afzhal R
AR
Lee
Katherine H
KH
Bindokas
Vytautus
V
D000818:Animals; D003652:Decanoic Acids / Q000494:pharmacology; D003981:Diazoxide / Q000494:pharmacology; D004596:Electroretinography; D019084:Fluorescent Antibody Technique, Indirect; D006880:Hydroxy Acids / Q000494:pharmacology; D019194:Ischemic Preconditioning; D008928:Mitochondria / Q000378:metabolism; D009569:Nitric Oxide / Q000378:metabolism; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism; D019335:Nitroarginine / Q000494:pharmacology; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D017382:Reactive Oxygen Species / Q000378:metabolism; D015427:Reperfusion Injury / Q000517:prevention & control*; D012160:Retina / Q000378:metabolism*; D012171:Retinal Vessels / Q000502:physiology*
D003652:Decanoic Acids; D006880:Hydroxy Acids; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D017382:Reactive Oxygen Species; C117780:mitochondrial K(ATP) channel; D019335:Nitroarginine; D009569:Nitric Oxide; C052853:5-hydroxydecanoic acid; D052250:Nitric Oxide Synthase Type III; D011493:Protein Kinase C; D003981:Diazoxide