Volume expansion-induced changes in renal tubular membrane protein phosphorylation

The influence of volume expansion (VE) on the in vitro phosphorylation of membrane protein in the proximal brush border membrane (BBM) of the thyroparathyroidectomized (TPTX) rat was studied in the presence and absence of cyclic AMP and the results were compared to those obtained in control TPTX and intact animals. The results indicate that the cyclic AMP-independent phosphorylation of a protein band (Mr = 72,000) was stimulated both by VE and by the presence of parathyroid hormone in the circulation, whereas the cyclic AMP-dependent phosphorylation of membrane proteins (Mr = 40,000, 52,000 and 87,000) was inhibited by the same maneuvers. These findings, taken together with data previously available, which demonstrate inhibition of BBM phosphate transport following VE, may provide a link between alterations in phosphate transport in renal BBM vesicles and the phosphorylation of membrane proteins. The results further suggest that membrane protein phosphorylation may be a common mechanism by which a number of agents and maneuvers induce an inhibition of renal tubular phosphate transport.