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We have used isoform-specific antibodies against the Na+, K(+)-ATPase alpha (alpha 1, alpha 2 and alpha 3) and beta (beta 1 and beta 2) subunit isoforms in order to establish their specific localization in isolated bovine articular chondrocytes. Immunoblotting confirmed the presence of the alpha 1 and alpha 3 isoforms, although alpha 1 expression was significantly greater than alpha 3 as assessed by immunofluorescence confocal laser scanning microscopy and PCR. A similar approach revealed the presence of the beta 1 and beta 2 isoforms in chondrocytes, although beta 2 immunostaining on the plasma membrane was more punctate than beta 1 which in contrast predominated in a subcellular compartment. The plasma membrane abundance of the Na+, K(+)-ATPase was found to be sensitive to the extracellular ionic concentration and long-term elevation of extracellular Na+ concentration significantly upregulated Na+, K(+)-ATPase density as measured by specific 3H-ouabain binding. Our observations suggest that the expression of alpha 3 and beta 2 is not restricted to excitable tissues as previously reported. The physiological relevance of alpha 3 expression in chondrocytes may be related to its low affinity for intracellular Na+ in an extracellular environment where Na+ concentration is unusually high (260-350 mM) compared to other cell types (140 mM). Glycoproteins and their branched carbohydrates have been implicated in cell recognition events, thus the beta 2 subunit glycoprotein may allow the chondrocyte to detect changes in its extracellular environment by physically interacting with components of the cellular cytoskeleton and matrix macromolecules.

Original publication




Journal article


Cell Biol Int

Publication Date





201 - 212


Animals, Antibodies, Blotting, Western, Cartilage, Articular, Cattle, Isoenzymes, Polymerase Chain Reaction, Sodium-Potassium-Exchanging ATPase