Parathyroid Hormone-dependent Uptake of Inorganic Phosphate by Mitochondria.

The role of the parathyroid hormone in the regulation of calcium and phosphate metabolism has been recognized for many years (1). At the cellular level, the hormone is thought to regulate calcium and phosphate transport reactions. It is now known to (a) increase calcium reabsorption in the renal tubule (2, 3), (b) increase the transport of calcium across intestinal membranes (a, 5), (c) increase bone mineral mobilization (I), and (d) stimulate the renal excretion of phosphate (6). Moreover, it has been suggested by several sources that the primary biochemical action of the hormone may be on some aspect of phosphate metabolism (7, 8). Studies with isolated mitochondria have provided a new approach to the study of parathyroid hormone action. DeLuca, Engstrom, and Rasmussen (9) have demonstrated that parathyroid hormone stimulates a vitamin D-dependent release of calcium from rat kidney mitochondria. In addition it has been found that the hormone stimulates inorganic phosphate uptake (10) and a phosphate-dependent, nonphosphorglative respiration (11). These effects, which were observed in oligomycininhibited mitochondria fortified with adcnosine triphosphate, were highly specific for the parathyroid hormone and did not depend upon the presence of vitamin D. These findings suggested that the primary effect of this hormone may be to control the translocation of phosphate across cellular and subcellular membranes. It is the purpose of this palmer to describe in detail the characteristics of the parathyroid hormone-dependent uptake of inorganic phosphate by isolated mitochondria.