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Am J Physiol Renal Physiol 295: F851-F856, 2008. First published July 30, 2008; doi:10.1152/ajprenal.90204.2008
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Intracellular pH regulates superoxide production by the macula densa

Ruisheng Liu, Oscar A. Carretero, Yilin Ren, Hong Wang, and Jeffrey L. Garvin

Hypertension and Vascular Research Division, Henry Ford Hospital, Detroit, Michigan

Submitted 21 March 2008 ; accepted in final form 23 July 2008

We hypothesized that elevated macula densa intracellular pH (pHi) during tubuloglomerular feedback enhances O2– production from NAD(P)H oxidase. Microdissected thick ascending limbs from rabbits with intact macula densa were cannulated and perfused with physiological saline. When luminal NaCl was switched from 10 to 80 mM, O2– production increased from 0.53 ± 0.09 to 2.62 ± 0.54 U/min (P < 0.01). To determine whether inhibiting the Na/H exchanger blocks O2– production, we used dimethyl amiloride (DMA) to block Na/H exchange. In the presence of DMA, O2– production induced by NaCl was blunted by 40%. To study the effect of pHi on O2– in intact macula densa cells, we measured O2– while pHi was changed by adjusting luminal pH. When the macula densa was perfused with 80 mM NaCl and the pH of the perfusate was switched to 6.8, 7.4, and 8.0, O2– production was significantly enhanced, but not at 10 mM NaCl. To ascertain the source of O2–, we used the NAD(P)H oxidase inhibitor apocynin. In the presence of apocynin (10–5 M), O2– production induced by elevating pHi was blocked. Finally, we measured the optimum pH for O2– production by the macula densa and found optimum extracellular pH is at 7.7 and optimum pHi is ~8 for O2– production. We found that elevated pHi enhances O2– production from NAD(P)H oxidase induced by increasing luminal NaCl when the lumen is perfused with 80 mM NaCl, not 10 mM, and O2– production is pH sensitive, with an optimum pHi of 8.

tubuloglomerular feedback; pH optimum; Na/H exchange; reactive oxygen species


Address for reprint requests and other correspondence: R. Liu, Dept. of Physiology and Biophysics, Univ. of Mississippi Medical Center. Jackson, MS 39216 (e-mail: rliu{at}physiology.umsmed.edu)




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