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Am J Physiol Renal Physiol 295: F726-F733, 2008. First published June 25, 2008; doi:10.1152/ajprenal.00137.2008
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Enhanced amiloride-sensitive superoxide production in renal medullary thick ascending limb of Dahl salt-sensitive rats

Paul M. O'Connor, Limin Lu, Carlos Schreck, and Allen W. Cowley, Jr.

Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin

Submitted 13 March 2008 ; accepted in final form 24 June 2008

The aims of the present study were to determine whether superoxide (O2–) production is enhanced in medullary thick ascending limb (mTAL) of Dahl salt-sensitive (SS) rats compared with a salt-resistant consomic control strain (SS.13BN) and to elucidate the cellular pathways responsible for augmented O2– production. Studies were carried out in 7- to 10-wk-old male SS and SS.13BN rats fed either a 0.4% NaCl diet or a 4.0% NaCl diet for 3 days before tissue harvest. Tissue strips containing mTAL were isolated from the left kidney, loaded with the O2–-sensitive fluorescent dye dihydroethidium, superfused with modified Hanks’ solution, and imaged at x60 magnification on a heated microscope stage. O2– production was stimulated in mTAL by incrementing superfusate NaCl concentration from 154 to 254 to 500 mM. O2– production was enhanced in mTAL of SS rats compared with SS.13BN rats in response to incrementing bath NaCl. Addition of N-methyl-amiloride (100 µM) or inhibition of NAD(P)H oxidase reduced O2– production in SS mTAL to levels observed in SS.13BN rats. Both amiloride- and ouabain-sensitive pathways of O2– production were elevated following 3 days of high (4.0%) NaCl feeding in mTAL of SS and SS.13BN rats. We conclude that mTAL from SS rats exhibit enhanced amiloride-sensitive O2– production. The amiloride-sensitive O2– response in mTAL is independent of active Na+ transport and appears to be mediated by NAD(P)H oxidase. Amiloride-sensitive O2– production is likely to contribute to augmented outer medullary O2– production observed in SS rats during both normal and high NaCl diets.

blood pressure; free radicals; hypertension; kidney; reduced nicotinamide adenine dinucleotide phosphatase oxidase


Address for reprint requests and other correspondence: P. M. O'Connor, Dept. of Physiology, Medical College of Wisconsin, 8701 Watertown Plank Rd., Milwaukee, WI 53202 (e-mail: poconnor{at}mcw.edu)






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