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Enhanced amiloride-sensitive superoxide production in renal medullary thick ascending limb of Dahl salt-sensitive rats

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.13^BN) 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.13^BN 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.13^BN 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.13^BN 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.13^BN 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

This article has been cited by other articles:

				P. M. O'Connor, L. Lu, M. Liang, and A. W. Cowley Jr A Novel Amiloride-Sensitive H+ Transport Pathway Mediates Enhanced Superoxide Production in Thick Ascending Limb of Salt-Sensitive Rats, Not Na+/H+ Exchange Hypertension, August 1, 2009; 54(2): 248 - 254. [Abstract] [Full Text] [PDF]