Parathyroid hormone as a calcium ionophore in bone cells: tests of specificity

Parathyroid Hormone (PTH) stimulates calcium entry into bone cells in vitro, and this effect has been proposed to mediate the actions of PTH on bone. Using cells harvested from infant rat calvaria by collagenase digestion, we evaluated the sensitivity and specificity of this phenomenon. Calcium uptake was temperature dependent, and was increased by PTH over the concentration range 0.01 to 0.50 units/ml. A series of nonhormonal peptides obtained during the purification of a single batch of PTH was found to stimulate calcium uptake. In addition, isoproterenol, ACTH, calcitonin, and glucagon stimulated calcium uptake. In no case, however, was the degree of stimulation as great as that produced by biologically active PTH. Prostaglandins are also potent resorbers of bone, and a series of prostaglandins also stimulated calcium uptake into bone cells. These results are compatible with a calcium ionophore model of PTH and prostaglandin action on bone.