Abstract
The plasma membrane abundance of the Na+/K+ pump or Na+,K+-ATPase depends on the intracellular concentration of Na+ in almost all animal cells. In cartilage, chondrocytes are surrounded by an extracellular matrix which consists of collagen and proteoglycan, a ground substance composed of glycosaminoglycan (GAG) side chains with a high fixed negative charge density. The polyanionic nature of the GAGs tends to draw monovalent cations into the matrix resulting in high [Na+] which may exceed 250 mM. As the concentration of GAGs in the tissue increases, so does [Na+]. In this study, it was found that the density of the Na+/K+ pump, measured by 3H-ouabain binding, correlates with the concentration of GAGs in the tissue. This indicates that chondrocytes are sensitive to their ionic environment and respond to local [Na+] variations by regulating the abundance of the Na+/K+ pump.