Bicarbonate-dependent pHi regulation by chondrocytes within the superficial zone of bovine articular cartilage

✍ Scribed by Victoria L. Simpkin; Dianne H. Murray; Andrew P. Hall; Andrew C. Hall

• Publisher: John Wiley and Sons
• Year: 2007
• Tongue: English
• Weight: 275 KB
• Volume: 212
• Category: Article
• ISSN: 0021-9541
• DOI: 10.1002/jcp.21054

✦ Synopsis

Abstract

Control of chondrocyte pH (pH~i~) determines articular cartilage matrix metabolism. However, the transporters of chondrocytes in situ throughout cartilage zones are unclear, and we tested the hypothesis that chondocytes within the superficial zone (SZ) utilise a HCO‐dependent system absent from other zones. Imaging of single BCECF‐labelled cells was used to monitor the pH~i~ of in situ chondrocytes within the cartilage zones, and also that of cells isolated from the SZ or full depth (FD) explants. Resting pH~i~ and intrinsic buffering power (β~i~) in HEPES‐buffered saline was not different between SZ and DZ cells, however the pH~i~ of SZ chondrocytes was lower in HCO saline. Ammonium pre‐pulse was used to acid‐load cells and pH~i~ recovery by in situ or isolated SZ chondrocytes shown to be totally dependent on HCO. pH~i~ recovery rate was significantly (P < 0.05) greater for in situ cells, suggesting that isolation damaged the HCO‐dependent system. Recovery of pH~i~ by in situ cells was blocked by the anion transport inhibitor DIDS, and partially inhibited by EIPA probably non‐specifically. Recovery of pH~i~ by acidified MZ or DZ cells or those isolated from FD explants was not affected by HCO (P > 0.05). Na^+^‐dependent HCO‐(NBC) transporters were identified in SZ chondrocytes by fluorescence immunohistochemistry suggesting that this system might account for the HCO‐dependent recovery of pH~i~. Bovine articular cartilage chondrocytes possess a HCO‐dependent transporter which plays a key role in pH~i~ regulation in cells in the SZ, but not in chondrocytes within deeper cartilage zones. J. Cell. Physiol. 212:600–609, 2007. © 2007 Wiley‐Liss, Inc.