Vasopressin-mediated protein phosphorylation in intact toad urinary bladder.

Endogenous protein phosphorylation was examined in intact 32P-labeled toad bladders in response to arginine vasopressin (AVP) and other agents under conditions where the bladders were undergoing the normal hydroosmotic response. AVP increased 32P incorporation into proteins with apparent MW of 17,000, 28,000 and 34,000 and decreased 32P incorporation into a protein with MW 15,500. The cyclic AMP analog 8-(p-chloro-phenylthio)-cyclic AMP mimicked the effects of AVP on 32P incorporation. AVP-dependent changes in protein phosphorylation were found to be specific for the epithelium of the bladder and were blocked by the antagonist d(CH2)5-D-TyrVAVP. AVP caused increased phosphorylation even in the absence of an osmotic gradient, but the AVP-mediated decrease in 32P content of the 15,500 MW band was observed only in the presence of an osmotic gradient. Isolated epithelial cells also displayed AVP-stimulated increases in 32P incorporation into the MW 17,000 and 34,000 phosphoproteins, but no decrease in 32P incorporation into the 15,500-dalton band. Phosphorylation of the MW 34,000 band was maximal within 3 min. These data are consistent with the hypothesis that physiological effects of AVP may, in part, be mediated by cyclic AMP-dependent phosphorylation of specific proteins.