Effect of hydrazine on transport on toad urinary bladder

Vasopressin stimulates osmotic water flow and urea permeability in the toad urinary bladder via separate cAMP-responsive mechanisms. Hydrazine (10--20 MM), added to the bladder's serosal bath, reversibly enhanced the effect of both low and saturating levels of vasopressin on osmotic water flow, without increasing urea permeability. A small increase in basal water flow was also observed. Cyclic AMP-stimulated water flow was not altered by hydrazine, but hydrazine enhanced the effect of both 8-bromo-cyclic AMP and methylisobutylxantine. Hydrazine increased luminal membrane aggregate frequency in vasopressin-treated tissues examined by freeze-fracture electron microscopy. Hydrazine increased both basal and vasopressin-stimulated adenylate cyclase activity. We could measure no effect of hydrazine on cAMP content; however hydrazine did increase the protein kinase activity ratio (-cAMP/+cAMP) in vasopressin-treated tissues, suggesting that the kinase activity ratio is more sensitive than cAMP content as an index of cAMP-related function in the bladder. Further strengthening the relationship between kinase activation and water flow, we found that methohexital, an inhibitor of vasopressin-stimulated water flow and adenylate cyclase, also decreased the kinase activity ratio in the presence of vasopressin. These studies link closely the role of cAMP-dependent kinase and luminal membrane aggregates to the specific mediation of vasopressin-stimulated water flow in the bladder.