Regulation of Na+, K+-ATPase density by the extracellular ionic and osmotic environment in bovine articular chondrocytes

The abundance of Na+, K+-ATPase in cartilage is controlled by the ionic com position of the extracellular environment of chondrocytes, and specifically depends on the local concentration of polyanionic matrix proteoglycans. In this study, it was found that the plasma membrane density of Na+, K+-ATPas e in isolated chondrocytes is sensitive to both ionic and osmotic changes i n the extracellular environment. The upregulation observed experimentally w as similar in magnitude as measured by H-3-ouabain binding, which indicates that chondrocytes respond adaptively to both ionic and osmotic stimuli. Th e precise mechanism for this novel mode of Na+, K+-ATPase regulation has ye t to be elucidated. Physiological perturbation of the ionic and osmotic env ironment of chondrocytes may alter intracellular Na+ concentration and this may be one of a number of stimuli responsible for alterations to the expre ssion and plasma membrane abundance of Na+, K+-ATPase in the cells.