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Intracellular pH regulates superoxide production by the macula densa

Ruisheng Liu1, Oscar A Carretero, Yilin Ren

  • 1Department of Physiology and Biophysics, University of Mississippi Medical Center, Jackson, MS 39216, USA. rliu@physiology.umsmed.edu

American Journal of Physiology. Renal Physiology
|August 1, 2008
PubMed

Insights

Elevated intracellular pH in macula densa cells boosts oxygen radical production from NAD(P)H oxidase, particularly at higher NaCl concentrations. This pH sensitivity is crucial for understanding tubuloglomerular feedback mechanisms.

Area of Science:

  • Renal Physiology
  • Cellular Biology
  • Biochemistry

Background:

  • Tubuloglomerular feedback (TGF) is a key intrarenal mechanism regulating glomerular filtration rate.
  • Macula densa cells play a critical role in sensing luminal NaCl concentration and initiating TGF.
  • The precise molecular mechanisms linking macula densa cell signaling to TGF, including reactive oxygen species (ROS) production, are not fully elucidated.

Purpose of the Study:

  • To investigate the hypothesis that elevated macula densa intracellular pH (pH(i)) enhances superoxide (O(2)(-)) production via NAD(P)H oxidase during TGF.
  • To determine the role of the Na/H exchanger in regulating pH(i) and subsequent O(2)(-) production.
  • To identify the optimal pH conditions for O(2)(-) production in macula densa cells.

Main Methods:

  • Microdissection and cannulation of rabbit thick ascending limbs with intact macula densa.
  • Perfusion with varying luminal NaCl concentrations and pH adjustments to manipulate intracellular pH.
  • Measurement of O(2)(-) production using fluorescence assays, with inhibition studies using dimethyl amiloride (DMA) and apocynin.

Main Results:

  • Increasing luminal NaCl from 10 to 80 mM significantly increased O(2)(-) production (0.53 to 2.62 U/min).
  • Inhibition of the Na/H exchanger with DMA blunted NaCl-induced O(2)(-) production by 40%.
  • Elevated luminal pH (7.4-8.0) at 80 mM NaCl enhanced O(2)(-) production, which was blocked by the NAD(P)H oxidase inhibitor apocynin, indicating pH(i) sensitivity with an optimum around pH 8.

Conclusions:

  • Elevated macula densa intracellular pH enhances O(2)(-) production from NAD(P)H oxidase, particularly under conditions of high luminal NaCl.
  • The Na/H exchanger plays a role in regulating macula densa pH(i) and subsequent ROS production.
  • These findings highlight the pH-dependent regulation of ROS production in macula densa cells, implicating NAD(P)H oxidase in TGF signaling.

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