Persistent stimulation of adenylate cyclase and urea transport by an AVP photolabel

The effects of a photoaffinity label for arginine vasopressin receptors, [Phe²,Phe(p-N₃)³]AVP (N₃-AVP), on urea permeability and adenylate cyclase activity have been investigated in the toad urinary bladder. This compound, when activated by ultraviolet light, induced a maximal and persistent increase in the urea permeability of the intact bladder and a persistent increase in the adenylate cyclase activity of toad bladder epithelial cell homogenates. Covalent attachment of the analogue to target tissue during photolysis was equivalent at 4 and 20°C. Bladders exposed to N₃-AVP in the presence of AVP during photolysis were substantially less permeable to urea than controls that had been exposed to N₃-AVP alone. These findings constitute further evidence in support of our previous suggestion that N₃-AVP binds covalently to AVP receptors and, in addition, demonstrates that N₃-AVP evokes a persistent increase in adenylate cyclase activity which, in turn, triggers a persistent increase in bladder permeability to urea.