The effect of environmental pH on glycosaminoglycan metabolism by normal human chondrocytes

The synthesis and release of sulfated glycosaminoglycans by normal human chondrocytes in culture are markedly affected by environmental pH. The biosynthetic rate is increased threefold as the pH of the growth medium is raised from 7.0 to 8.0. This coincides with a corresponding elevation in total protein and cell growth. The rate of release of newly synthesized sulfated glycosaminoglycans from the cell layer as well as their distribution between intra- and extracellular localization in the cell layer is also modulated by environmental pH. At pH 8, 35 per cent is found within the cells; this value is reduced to 13 per cent at pH 7. Pulse-chase experiments showed that previously incorporated sulfated proteoglycans were released at a faster rate at pH 7 than at pH 8. The data suggest that proton concentrations affect the biosynthesis and the mode of distribution of newly synthesized sulfated glycosaminoglycans.