CONCERNING pH GRADIENTS BETWEEN THE EXTRACELLULAR COMPARTMENT AND FLUIDS BATHING THE BONE MINERAL SURFACE AND THEIR RELATION TO CALCIUM ION DISTRIBUTION*

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Abstract
Surviving and heat-inactivated bone samples (mouse) calvaria) were incubated in vitro in media of different pH, and Ca and P concentrations in the media were measured. The ability of actively metabolizing bone samples to maintain higher Ca concentrations in their surrounding media than inactivated samples was abolished when pH in the media was decreased from about 7 to 6.5. This occurred while cellular metabolism continued at the same rate, as judged from lactate production. P concentrations were the same for both groups. These findings are consistent with the view that cellular metabolic effects on Ca concentration in the medium are mediated, at least in part through pH gradients between the bone fluid compartment and the medium. By analogy, the results support the concept that the existence of a pH gradient between a fluid phase in bone and the circulating fluids is a factor underlying the apparent supersaturation of normal serum with respect to bone mineral.