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Rapid effects of hypoxia on H+ homeostasis in articular chondrocytes

  • Ion Channels, Receptors and Transporters
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Abstract

Articular chondrocytes experience low oxygen (O2) levels compared with many other tissues, and values fall further in disease states. Chondrocyte intracellular pH (pHi) is a powerful modulator of matrix synthesis and is principally regulated by Na+-H+ exchange (NHE). In equine chondrocytes, NHE is inhibited when cells are incubated for 3 h at low O2, leading to intracellular acidosis. O2-dependent changes in reactive oxygen species (ROS) levels appear to underlie this effect. The present study examines whether hypoxia can influence chondrocyte NHE activity and pHi over shorter timescales using the pH-sensitive fluoroprobe BCECF in cells isolated not only from equine cartilage but also from bovine tissue. O2 levels in initially oxygenated solutions gassed with N2 fell to approximately 1% within 2 h. A progressive fall in pHi and acid extrusion capacity was observed, with statistically significant effects (P < 0.05) apparent within 3 h. For equine and bovine cell populations subjected to step change in O2 by resuspension in hypoxic (1%) solutions, a decline in acid extrusion and pHi was observed within 10 min and continued throughout the recording period. This effect represented inhibition of the NHE-mediated fraction of acid extrusion. Cells subjected to hypoxic solutions supplemented with CoCl2 (100 μM) or antimycin A (100 µM) to raise levels of ROS did not acidify. The conserved nature and rapidity of the response to hypoxia has considerable implications for chondrocyte homeostasis and potentially for the maintenance of cartilage integrity.

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Acknowledgements

We thank the Horserace Betting Levy Board, the Arthritis Research Campaign, and the Sir Halley Stewart Trust for financial support.

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Authors and Affiliations

  1. Department of Physiology, Anatomy and Genetics, Sherrington Building, Parks Road, Oxford, OX1 3PT, UK

    David McCartney, Joanna Sumpter, Thomas P. A. Fairfax & Robert J. Wilkins

  2. Department of Veterinary Medicine, Madingley Road, Cambridge, CB3 OES, UK

    John S. Gibson

  3. Faculty of Veterinary Science, University of Liverpool, Neston, Cheshire, CH64 7TE, UK

    Peter I. Milner & Hannah L. Edwards

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  1. John S. Gibson
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  2. David McCartney
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  3. Joanna Sumpter
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  4. Thomas P. A. Fairfax
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  5. Peter I. Milner
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  7. Robert J. Wilkins
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Correspondence to Robert J. Wilkins.

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Gibson, J.S., McCartney, D., Sumpter, J. et al. Rapid effects of hypoxia on H+ homeostasis in articular chondrocytes. Pflugers Arch - Eur J Physiol 458, 1085–1092 (2009). https://doi.org/10.1007/s00424-009-0695-6

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  • DOI: https://doi.org/10.1007/s00424-009-0695-6

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