Increase of sodium delivery stimulates the mitochondrial respiratory chain H2O2 production in rat renal medullary thick ascending limb

Ohsaki Y, O'Connor P, Mori T, Ryan RP, Dickinson BC, Chang CJ, Lu Y, Ito S, Cowley AW, Jr. Increase of sodium delivery stimulates the mitochondrial respiratory chain H2O2 production in rat renal medullary thick ascending limb. Am J Physiol Renal Physiol 302: F95-F102, 2012. First published October 5, 2011; doi:10.1152/ajprenal.00469.2011.-The mitochondria-rich epithelial cells of the renal medullary thick ascending limb (mTAL) reabsorb nearly 25% of filtered sodium (Na+) and are a major source of cellular reactive oxygen species. Although we have shown that delivery of Na+ to the mTAL of rats increases superoxide (O-2(-)) production in mTAL, little is known about H2O2 production, given the lack of robust and selective fluorescent indicators for determining changes within the whole cell, specifically in the mitochondria. The present study determined the effect of increased tubular flow and Na+ delivery to mTAL on the production of mitochondrial H2O2 in mTAL. H2O2 responses were determined in isolated, perfused mTAL of Sprague-Dawley rats using a novel mitochondrial selective fluorescent H2O2 indicator, mitochondria peroxy yellow 1, and a novel, highly sensitive and stable cytosolic-localized H2O2 indicator, peroxyfluor-6 acetoxymethyl ester. The results showed that mitochondrial H2O2 and cellular fluorescent signals increased progressively over a period of 30 min following increased tubular perfusion (5-20 nl/min), reaching levels of statistical significance at similar to 10-12 min. Responses were inhibited with rotenone or antimycin A (inhibitors of the electron-transport chain), polyethylene glycol-catalase and by reducing Na+ transport with furosemide or ouabain. Inhibition of membrane NADPH-oxidase with apocynin had no effect on mitochondrial H2O2 production. Cytoplasmic H2O2 (peroxyfluor-6 acetoxymethyl ester) increased in parallel with mitochondrial H2O2 (mitochondria peroxy yellow 1) and was partially attenuated (similar to 65%) by rotenone and completely inhibited by apocynin. The present data provide clear evidence that H2O2 is produced in the mitochondria in response to increased flow and delivery of Na+ to the mTAL, and that whole cell H2O2 levels are triggered by the mitochondrial reactive oxygen species production. The mitochondrial production of H2O2 may represent an important target for development of more effective antioxidant therapies.