Renal oxidative stress in medullary thick ascending limbs produced by elevated NaCl and glucose.
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 micromol/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 micromol/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.
Mori
Takefumi
T
Department of Physiology, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA. tmori@mcw.edu
Cowley
Allen W
AW
D000818:Animals; D046508:Culture Techniques; D005947:Glucose / Q000494:pharmacology*; D007679:Kidney Medulla / Q000187:drug effects / Q000378:metabolism*; D008138:Loop of Henle / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D018384:Oxidative Stress; D051381:Rats; D017207:Rats, Sprague-Dawley; D012965:Sodium Chloride / Q000494:pharmacology*; D017923:Sodium-Hydrogen Exchangers / Q000502:physiology; D000254:Sodium-Potassium-Exchanging ATPase / Q000502:physiology; D013481:Superoxides / Q000378:metabolism*; D014284:Triiodothyronine / Q000494:pharmacology
D017923:Sodium-Hydrogen Exchangers; D014284:Triiodothyronine; D013481:Superoxides; D012965:Sodium Chloride; D000254:Sodium-Potassium-Exchanging ATPase; D005947:Glucose