Cyclic AMP-dependent protein phosphorylation and dephosphorylation alter phosphate transport in canine renal brush...

We have previously demonstrated that the cAMP-dependent phosphorylation of two or more proteins (bands IX and V) in membrane vesicles isolated from the renal brush border from kidneys of dogs, was associated with decreased Na+-dependent Pi transport. In the present studies a specific dephosphorylation of band IX was demonstrated in brush border vesicles incubated in the absence of F- which had been used in previous studies to inhibit phosphoprotein phosphatase activity. Dephosphorylation of band IX was 80% complete after 5 min of incubation at which time inhibition of Pi transport in membrane vesicles which had been phosphorylated in the presence of cAMP could no longer be demonstrated. Dephosphorylation of band IX was no different in vesicles from kidneys originating from parathyroidectomized dogs prior to or following the administration of parathyroid hormone in vivo and normal dogs. We conclude that the cAMP-dependent phosphorylation of brush border membrane proteins may mediate a phosphaturic effect of the hormone. Parathyroid hormone-induced phosphaturia may be terminated through the action of a specific membrane phosphoprotein-phosphatase.