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Am J Physiol Regul Integr Comp Physiol 290: R79-R83, 2006. First published August 11, 2005; doi:10.1152/ajpregu.00447.2005
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Cardiovascular-Kidney Interactions in Health and Disease

Differential effects of superoxide on luminal and basolateral Na+/H+ exchange in the thick ascending limb

Ramiro Juncos,1 Nancy J. Hong,1 and Jeffrey L. Garvin1,2

1Division of Hypertension and Vascular Research, Henry Ford Hospital, Detroit; and 2Department of Physiology, Wayne State University, Detroit, Michigan

Submitted 24 June 2005 ; accepted in final form 8 August 2005

Superoxide (O2–) increases Na+ reabsorption in the thick ascending limb (THAL) by enhancing Na/K/2Cl cotransport. However, the effects of O2– on other THAL transporters, such as Na+/H+ exchangers, are unknown. We hypothesized that O2– stimulates Na+/H+ exchange in the THAL. We assessed total Na+/H+ exchange activity by measuring recovery of intracellular pH (pHi) after acid loading in isolated perfused THALs before and after adding xanthine oxidase (XO) and hypoxanthine (HX). We found that XO and HX decreased total pHi recovery rate from 0.26 ± 0.05 to 0.21 ± 0.04 pH units/min (P < 0.05), and this net inhibition decreased steady-state pHi from 7.52 to 7.37. Because THALs have different Na+/H+ exchanger isoforms on the luminal and basolateral membrane, we tested the effects of xanthine oxidase and hypoxanthine on luminal and basolateral Na+/H+ exchange by adding dimethylamiloride to either the bath or lumen. Xanthine oxidase and hypoxanthine increased luminal Na+/H+ exchange from 3.5 ± 0.8 to 6.7 ± 1.4 pmol·min–1·mm–1 (P < 0.01) but decreased basolateral Na+/H+ exchange from 10.8 ± 1.8 to 6.8 ± 1.1 pmol·min–1·mm–1 (P < 0.007). To ascertain whether these effects were caused by O2– or H2O2, we examined the ability of tempol, a superoxide dismutase mimetic, to block these effects. In the presence of tempol, xanthine oxidase and hypoxanthine had no effect on luminal or basolateral Na+/H+ exchange. We conclude that O2– inhibits basolateral and stimulates luminal Na+/H+ exchangers, perhaps because different isoforms are expressed on each membrane. Inhibition of basolateral Na+/H+ exchange may enhance stimulation of luminal Na+/H+ exchange by providing additional protons to be extruded across the luminal membrane. Together, the effects of O2– on Na+/H+ exchange may increase net HCO3– reabsorption by the THAL.

reactive oxygen species; intracellular pH; superoxide dismutase


Address for reprint requests and other correspondence: Corresponding author: J. L. Garvin, Hypertension and Vascular Research Division, Henry Ford Hospital, 2799 West Grand Blvd., Detroit, MI 48202–2689 (e-mail: jgarvin1{at}hfhs.org)




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