Sodium transport systems in human chondrocytes I. Morphological and functional expression of the Na+,K+-ATPase a and β subunit isoforms in healthy and arthritic chondrocytes

• Trujillo, E. ^[1] ; Alvarez de la Rosa, D. ^[1] ; Mobasheri, A. ^[2] ; Ávila, J. ^[1] ; Gonzalez, T. ^[3] ; Martín Vasallo, P. ^[1]
  1. [1] Universidad de La Laguna

     Universidad de La Laguna

     San Cristóbal de La Laguna, España

     
  2. [2] University of Westminster

     University of Westminster

     Reino Unido

     
  3. [3] Rheumatology Service, Universitary Hospital of Canarias, La Cuesta, Tenerife

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• Localización: Histology and histopathology: cellular and molecular biology, ISSN-e 1699-5848, ISSN 0213-3911, Vol. 14, Nº. 4, 1999, págs. 1011-1022
• Idioma: inglés
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  • The chondrocyte is the cell responsible for the maintenance of the articular cartilage matrix. The negative charges of proteoglycans of the matrix draw cations, principally Na+, into the matrix to balance the negative charge distribution. The Na+,Kf -ATPase is the plasma membrane enzyme that maintains the intracellular Na+ and K+ concentrations. The enzyme is composed of an a and a l3 subunit, so far, 4 a and 3 B isoforms have been identified in mammals. Chondrocytes are sensitive to their ionic and osmotic environment and are capable of adaptive responses to ionic environmental perturbations particularly changes to extracellular [Na+]. In this article we show that human fetal and adult chondrocytes express three a ( a l , a 2 and the neural form of a3) and the three l3 isoforms (131, l32 and 83) of the Na+,K+-ATPase. The presence of multiple Na+,K+-ATPase isoforms in the plasma membrane of chondrocytes suggests a variety of kinetic properties that reflects a cartilage specific and very fine specialization in order to maintain the Na+/K+ gradients. Changes in the ionic and osmotic environment of chondrocytes occur in osteoarthritis and rheumatoid arthritis as result of tissue hydration and proteoglycan loss leading to a fall in tissue Na+ and K+ content. Although the expression levels and cellular distribution of the proteins tested do not vary, we detect changes in p-nitrophenylphosphatase activity "in situ" between control and pathological samples. This change in the sodium pump enzymatic activity suggests that the chondrocyte responds to these cationic environmental changes with a variation of the active isozyme types present in the plasma membrane.