Morphochemical analysis of phosphorus pools in calcifying cartilage.

The objective of this investigation was to measure phosphorus (P) levels in the epiphyseal growth cartilage and to relate pool sizes to chondrocyte maturation and tissue mineralization. To carry out these studies, we utilized a morphochemical technique that permitted measurements of insoluble mineral phosphate, soluble inorganic phosphate (Pi), low and high molecular weight phosphorylated macromolecules and lipid P in freeze-trapped histological sections. Analysis of the sections revealed that very low levels of P are present in pre-mineralized cartilage; at the mineralization front, a large increase in Pi is correlated with mineral formation. Moreover, with calcification of the cartilage, a decrease in the concentration of low molecular weight compounds was observed. It is suggested that these latter components may provide the initial source of Pi for the development of mineral. The results of the study support the view that metabolic regulation of P pool size may be a rate-limiting factor in the mineralization of cartilage.