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(Hypertension. 2004;43:341.)
© 2004 American Heart Association, Inc.

Scientific Contribution

Renal Oxidative Stress in Medullary Thick Ascending Limbs Produced by Elevated NaCl and Glucose

From the Department of Physiology, Medical College of Wisconsin, Milwaukee.

Correspondence to Takefumi Mori, MD, PhD, Department of Physiology, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226.E-mail tmori{at}mcw.edu

The effects of NaCl, glucose, and thyroid hormone on the production of superoxide (O₂^·-) within the renal medulla of Sprague-Dawley rats were examined. Responses of intracellular superoxide [O₂^·-]_i in isolated medullary thick ascending limbs (mTALs) were studied using real-time fluorescent microscopy with measurement of the dehydroethidium (DHE) to ethidium (Eth) conversion ratio (Eth/DHE ratio unit). The results demonstrated that elevations of extracellular NaCl (from 152 to 252 mmol/L), D-glucose (from 5 to 25 mmol/L), and triiodo-thyronine (T3; 10 µmol/L) significantly increased [O₂^·-]_i levels. Preincubation with superoxide scavenger 4,5-dihydroxy-1,3-benzene-disulfonic acid (1 mmol/L) significantly inhibited these responses. Stimulation with equamolar amounts of choline chloride or L-glucose failed to increase [O₂^·-]_i, indicating that these O₂^·- responses were not determined by changes in osmolality. The responses to NaCl, D-glucose, and T3 were abolished by pretreatment with the Na⁺/K⁺-ATPase pump inhibitor ouabain (4 mmol/L) and with Na⁺/H⁺ -exchanger inhibitor dimethylamiloride (100 µmol/L). We conclude that elevations of extracellular NaCl, D-glucose, or T3 levels can activate both the Na⁺/K⁺-ATPase pump and Na⁺/H⁺ exchanger in mTAL, which, in turn, is associated with increased intracellular concentrations of superoxide.

Key Words: oxidative stress • Na⁺, K⁺-transporting ATPase • sodium pump • antiporters • diabetes mellitus • hypertension, sodium-dependent • fluorescence