Urea transport across urinary bladder and salt acclimation in toad (Bufo viridis

Physiol. 258 (Regulatory Integrative Comp. Physiol. 27): R883-R888, 1990.-The fluxes of urea across the urinary bladder of the toad Bufo viridis have been studied under conditions of acclimation to tap water or 500 mosM NaCl solution. The [14C]urea fluxes were measured simultaneously with [3H]inulin to test for nonspecific leakage. The fluxes are quite high (K,,,,, = 75 x 10m7 cm/s at 5 mmol/l urea) and are similar in either the mucosal-to-serosal or the opposite direction. “Summer” rates were five to six times higher than the “winter ” rates. Antidiuretic hormone (ADH), theophylline, and forskolin in-creased the fluxes to variable degrees (two to five times), similar in the two acclimation conditions. Phloretin inhibited the urea fluxes by nearly 50%. 1,3-Dimethylurea and thiourea, but not acetamide, competed with the urea fluxes effectively. The fluxes of urea were not affected by the osmotic water flow, althoug