ULTRASTRUCTURAL CORRELATES OF THE ANTIDIURETIC HORMONE-DEPENDENT AND ANTIDIURETIC HORMONE-INDEPENDENT INCREASE OF OSMOTIC WATER PERMEABILITY IN THE FROG URINARY-BLADDER EPITHELIUM

Electron and confocal microscopy, using immunocytochemical methods, wa s employed to assess osmotic water permeability of the frog (Rana temp oraria) urinary bladder during transcellular water transport, induced by antidiuretic hormone (ADH) or by wash-out of autacoids from serosal , ADH-free Ringer solution. The increase of osmotic water permeability of the urinary bladder was accompanied by relevant ultrastructural ch anges, the most remarkable being: (1) the appearance of aggregates of intramembranous particles in the apical membrane of granular cells, an d the extent of the membrane area covered by the aggregates proportion al to that of the water flow; (2) redistribution of actin filaments in the cytoplasm of granular cells; judging from the anti-actin label de nsity, the number of actin filaments in the apical region of cytoplasm was reduced by 2.5-4 times compared with normal; (3) a decrease in th e total electron density of the cytoplasm due to the increased water c ontent of granular cells.