Publication: Sodium transport systems in human chondrocytes
Morphological and functional expression of the
Na+,K+-ATPase a and D subunit isoforms in
healthy and arthritic chondrocytes
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Date
1999
Authors
Trujillo, E. ; Alvarez de la Rosa, D. ; Mobasheri, A. ; Ávila, J. ; Gonzalez, T. ; Martín Vasallo, P.
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Publisher
Murcia : F. Hernández
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DOI
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info:eu-repo/semantics/article
Description
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+,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.
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