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S. Roth, J.C. Dreixler, A.R. Shaikh, K. Lee; Mitochondrial KATP Channel and Retinal Ischemic Preconditioning . Invest. Ophthalmol. Vis. Sci. 2006;47(13):497.
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To examine the mechanisms of ischemic preconditioning (IPC) related to opening of mitochondrial KATP (mKATP) channels in the retina.
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. Using immunohistochemistry and image analysis, changes in levels of reactive oxygen species (ROS) and NOS subtypes were measured and their cellular localization determined.
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). Non–specific blockade of NOS by Nω–Nitro–L–arginine (L–NNA), but not by specific inducible NOS (iNOS) or neuronal NOS (nNOS) 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 co–localized with e– and nNOS in retinal cells following stimulation with diazoxide.
We showed that ischemic preconditioning 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.
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