CALCIUM METABOLISM OF BONE IN VITRO. INFLUENCE OF BONE CELLULAR METABOLISM AND PARATHYROID HORMONE*

Abstract

Mouse calvaria were incubated in vitro until a steady state distribution of Ca and P between medium and sample was reached. These studies were designed to examine the relative importance of passive mineral solubility and various aspects of bone cellular metabolism in the maintenance of Ca and P concentrations in body fluids. Inactivation of cellular activity by heat and by long-lasting starvation depressed Ca concentrations in the media 17.6 and 12.6%, respectively. In surviving bone, glucose deprivation and iodoacetate (IA) inhibition decreased Ca 8.2 and 5.9%, respectively, and lactate production about 94%. These differences were all highly significant (p < 0.001). P concentrations, however, were roughly the same in all experiments with surviving bones. While anaerobiosis increased lactate production 15.3%, Ca was slightly decreased. The results support the concept that mobilization of Ca and P from bone mineral and the regulation of serum levels of these ions are dependent upon the rate and pattern of bone cell metabolism. Effects of glucose metabolism are dependent upon steps beyond triose phosphate dehydro-genase, but the rate of lactate production seems only indirectly involved. Prior treatment with parathyroid extract (PTE) increased Ca 16.8 and lactate 22.3% in the media surrounding surviving bones. The increment in Ca concentration due to the hormone treatment appeared to be the result of (a) an increase in passive solubility of the mineral, and (b) a modification of the pattern of cellular metabolic effects.