title: Sodium transport systems in human chondrocytes. I. Morphological and functional expression of the Na+,K(+)-ATPase alpha and beta subunit isoforms in healthy and arthritic chondrocytes.
abstract: 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+,K(+)-ATPase is the plasma membrane enzyme that maintains the intracellular Na+ and K+ concentrations. The enzyme is composed of an alpha and a beta subunit, so far, 4 alpha and 3 beta 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 alpha (alpha 1, alpha 2 and the neural form of alpha 3) and the three beta isoforms (beta 1, beta 2 and beta 3) 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.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of La Laguna, Tenerife, Spain.
authors.forename: E
authors.initials: E
authors.lastname: Trujillo
authors.forename: D
authors.initials: D
authors.lastname: Alvarez de la Rosa
authors.forename: A
authors.initials: A
authors.lastname: Mobasheri
authors.forename: J
authors.initials: J
authors.lastname: Avila
authors.forename: T
authors.initials: T
authors.lastname: González
authors.forename: P
authors.initials: P
authors.lastname: Martín-Vasallo
mesh_terms: D000328:Adult; D000818:Animals; D001172:Arthritis, Rheumatoid / Q000201:enzymology* / Q000473:pathology; D001692:Biological Transport; D002358:Cartilage, Articular / Q000196:embryology / Q000201:enzymology; D019902:Chondrocytes / Q000201:enzymology*; D006801:Humans; D007527:Isoenzymes / Q000032:analysis / Q000235:genetics; D010003:Osteoarthritis / Q000201:enzymology* / Q000473:pathology; D051381:Rats; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000032:analysis* / Q000235:genetics
chemical_list: D007527:Isoenzymes; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase