Cellular Control of Calcium Movements in Bone. Interrelationships of the Bone Membrane, Parathyroid Hormone and Alkaline Phosphatase

Bone ECF is separated from the general ECF by a functional membrane which has been shown to limit the mineralization of embryonic tibiae and to selectively pump Ca out of the bone ECF. Energy to run this pump may be derived from ATP hydrolyzed by Ca-2+-stimulated ATPase, an enzyme activity which bone alkaline phosphatase may possess. The data suggest that PTH rapidly and selectively increases Ca pumping possibly by increasing ATPase activity in the bone cell cytosol through increased Ca influx and by increasing the intracellular ATPase level through inhibited secretion or excretion of the enzyme.