MEDIUM PH MODULATES MATRIX, MINERAL, AND ENERGY-METABOLISM IN CULTURED CHICK BONES AND OSTEOBLAST-LIKE CELLS

The effects of medium pH were tested on calvariae, tibiae, and osteobl ast-like cells from chick embryos. Bones and isolated cells were incub ated for 5 h or 2 days in Hepes-buffered medium at pH values ranging f rom 6.8 to 8.2. Osteoblast function was evaluated by lactate productio n, oxygen consumption, alkaline phosphatase activity (AlPase), Ca and inorganic phosphate (P-i) flux, proline hydroxylation, DNA content, an d thymidine incorporation. As medium pH was increased, glycolysis, col lagen synthesis, and AlPase increased, while Ca efflux decreased. No e ffect of pH was seen on mitochondrial activity, P-i efflux, or cell nu mber or proliferation. The importance of glycolysis as an endogenous p H regulator was demonstrated by inhibition with iodoacetic acid or glu cose restriction and by adding lactate to the medium. The results sugg est that the pH of bone interstitial fluid may be regulated by glycoly sis and that changes in pH of this compartment may have marked effects on osteoblast function.