Bone cell calcium stores: their size, location and kinetics of exchange.

Abstract

The mean calcium content of a mixed population of viable bone cells freshly separated from the calcified bone matrix has been found to be 194.5±7.3 mmoles/kg wet weight in pigs and 176.6±8.7mmoles/kg in rats. The calcium appears to be intracellular, the major portion (90% or more) sedimenting readily with intracellular particles in a centrifugal field and the balance being largely in the cell sap. Kinetic studies using45Ca indicate rapid temperature-dependent turnover of the calcium in both soluble and particulate calcium pools of bone cell homogenates and a direct exchange between each pool and the extracellular medium, each occurring at a different rate and possibly by different mechanisms, the particulate pool being the more rapid. These data suggest that the particulate pool may correspond to the small dense granules recently identified in bone cells by electron microscopy and that the uptake, storage and release of calcium from these stores may be important in skeletal calcium metabolism.