Cyclic AMP-dependent protein phosphorylation in canine renal brush-border membrane vesicles is associated with decreased phosphate transport

It is known that the administration of parathyroid hormone to dogs results in phosphaturia and decreased phosphate transport in brush-border vesicles isolated from the kidneys of those dogs. Parathyroid hormone has been shown to activate adenylate cyclase at the basal-lateral membrane of the renal proximal tubular cell. It has been postulated that parathyroid hormone-induced phosphaturia is effected through phosphorylation of brush-border protein by membrane-bound cAMP-dependent protein kinase. An experimental system was designed such that phosphorylation of brush-border vesicles and Na⁺-stimulated solute transport could be studied in the same preparations. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of membrane vesicles revealed cAMP-dependent phosphorylation of 2 protein bands (M(r)= 96,000 and 62,000), which was enhanced by exposure of the inside of the membrane vesicles to ATP and cAMP. Cyclic AMP-dependent phosphorylation of brush-border vesicles was accompanied by inhibition of Na⁺-stimulated P(i) but not D-glucose transport or ²²Na⁺ uptake. When renal brush-border vesicles from parathyroidectomized and normal dogs were phosphorylated in vitro in the presence and absence of cAMP, both the cAMP-dependent phosphorylation and inhibition of Na⁺-stimulated P(i) transport were greater in vesicles isolated from kidneys of parathyroidectomized dogs relative to control animals. We conclude that the cAMP-dependent phosphorylation of brush-border membrane-vesicle proteins is associated with specific inhibition of Na⁺-stimulated P(i) transport. The phosphaturic action of parathyroid hormone (PTH) could be mediated through the cAMP-dependent phosphorylation of specific brush-border membrane proteins.