Composition of the mineral deposited during in vitro calcification in relation to the fluid phase

Abstract Despite the fact that in vitro calcification of rachitic epiphyseal cartilage has been extensively employed in studies of the mechanism of calcification, the chemical composition of the solid deposited was not hitherto investigated. The present investigation is a study of the mineral deposited during in vitro calcification of the matrix of hypertrophic rachitic epiphyseal cartilage from calcifying solutions of different compositions. The solids deposited and the solutions used were analysed for calcium, phosphate, and carbonate by methods described herein. The CO 3 :PO 4 and Ca:PO 4 ratios of the solid were linearly related to those of the fluid within the range of solution compositions used. The increase in the Ca:PO 4 ratio of the solids as the Ca:PO 4 and CO 3 :PO 4 ratios of the solution were raised was due to increased deposition of CaCO 3 . Although the compositions of the solid varied, the residual Ca:PO 4 ratio was 1.33 in all cases. The Ca:PO 4 ratio of 1.33 corresponds to that of octocalcium phosphate or may represent a defect apatite. The low Ca:PO 4 ratios found in in vitro calcification resembles the compositions usually found in young bone, and may represent the composition of newly deposited bone mineral in vivo .