Cellular and Molecular Biology

Sodium transport systems in human chondrocytes II. Expression of ENaC, Na+/K+/2Cl- cotransporter and Na+/H+ exchangers in healthy and arthritic chondrocytes

E. Trujillo1,2, D. Alvarez de la Rosa1, A. Mobasheri3, T. González2, C.M. Canessa4 and P. Martín-Vasallo1

1Laboratory of Developmental Biology, Department of Biochemistry and Molecular Biology, University of La Laguna, La Laguna, Tenerife, Spain, 2Rheumatology Service, Universitary Hospital of Canarias, La Cuesta, Tenerife, Spain, 3Department of Biomedical Sciences, School of Biosciences, University of Westminster, London, United Kingdom and 4Department of Molecular and Cellular Physiology, Yale University School of Medicine, New Haven, USA

Offprint requests to: Pablo Martín-Vasallo, MD, PhD, Laboratorio de Biología del Desarrollo (LBD), Departamento de Bioquímica y Biología Molecular, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain. Fax: 34.922.318354. e-mail: pmartin@ull.es


Summary. In this article, the second of two, we continue our studies of sodium-dependent transport systems in human cartilage from healthy individuals and with osteoarthritis (OA) and rheumatoid arthritis (RA). We demonstrate the presence of the epithelial sodium channel (ENaC), previously undescribed in chondro-cytes. This system is composed of three subunits, a, ß and g. We have shown that the human chondrocytes express at least the a and the ß subunit of ENaC. The expression of these subunits is altered in arthritic chondrocytes. In RA samples the quantity of a and ß is significantly higher than in control samples. On the other hand, ENaC a and ß subunits are absent in the chondrocytes of OA cartilage. Human chondrocytes also possess three isoforms of the Na+/H+ exchanger (NHE), NHE1, NHE2 and NHE3. The NHE system is composed of a single protein and is believed to participate in intracellular pH regulation. Furthermore, our studies indicate that at least one isoform of the electroneutral Na+/K+/2Cl- cotransporter (NKCC) is present in human chondrocytes. There are no obvious variations in the relative expression of NHE isoforms or NKCC between healthy and arthritic cartilage. Our data suggests that chondrocytes from arthritic cartilage may adapt to changes in their environmental sodium concentration through variations in ENaC protein levels. ENaC is also likely to serve as a major sodium entry mechanism, a process that, along with cytoskeletal proteins, may be part of mechanotransduction in cartilage. Histol. Histopathol. 14, 1023-1031 (1999)

Key words: Epithelial sodium channel, Na+/H+ exchanger, Na+,K+,2Cl- cotransporter, Osteoarthritis, Rheumatoid arthritis

DOI: 10.14670/HH-14.1023