Calcium homeostasis. III: The bone membrane potential and mineral dissolution.

Active ionic transport through the bone membrane appears to be involved in the regulation of calcium level in the bloodstream. This transport process can be monitored by the transmembrane electrical potential difference, which increases in the presence of parathyroid hormone. The present work is an evaluation of the constraints placed on the system by the solubility limit of the mineral phase. A thermodynamic analysis demonstrates that control of mineral dissolution can only occur when the transported species is one of the mineral phase constituents. A combination of previous experimental results with the present development limits the possible active transport mechanism responsible for the adjustment of mineral dissolution/deposition to: an outward-directed pump for hydroxyl ion, an outward-directed pump for phosphate ion, or an inward-directed pump for hydrogen ion.