Effect of metabolic inhibitors on vasopressin‐stimulated transport systems in the toad bladder

Abstract

Vasopressin increases the permeability of receptor cells to water and, in tissues such as toad bladder, to solutes such as urea. While cyclic AMP appears to play a major role in mediating the effects of vasopressin, there is evidence that activation of the water permeability system and the urea permeability system involves separate pathways. In the present study, we have shown that inhibitors of oxidative metabolism (rotenone, dinitrophenol, and methylene blue) selectively inhibit either vasopressin-stimulated water flow or vasopressin-stimulated urea transport. There was no inhibition, however, when exogenous cyclic AMP was substituted for vasopressin, and little to no inhibition when the potent analogue 8-bromoadenosine 3',5'-cyclic monophosphate (8-Br-cAMP) was employed. Rotenone had no effect on adenylate cyclase activity or cyclic AMP levels within the cell; dinitrophenol decreased adenylate cyclase activity minimally. Additional studies with vinblastine and nocodazole, inhibitors of microtubule assembly, demonstrated an inhibition of vasopressin and cyclic AMP-stimulated water flow but showed no effect on urea transport. We would conclude that water and urea transport, as examples of hormone-stimulated processes, have different links to cell metabolism, and that in addition to cyclic AMP, a non-nucleotide pathway may be involved in the action of vasopressin.

Membrane pathways for water and solutes in the toad bladder: I. Independent activation of water and urea transport

“…Recent studies (Levine et aI., 1976b) have shown that these agents are potent inhibitors of toad bladder adenylate cyclase. Similar results have been obtained with the metabolic inhibitors rotenone and dinitrophenol, which selectively inhibit water flow at an early step in the cyclic nucleotide sequence; methylene blue, on the other hand, inhibits urea transport, but not water flow, and appears to act prior to the generation of cyclic AMP (Hays, Franki & Ross, 1979). These early selective effects are not confined to inhibitory agents; hydrazine, which stimulates toad bladder adenylate cyclase, selectively enhances vasopressin-stimulated water flow, with no change in urea or sodium transport (Levine et al, 1977).…”