Cytoplasmic to Luminal Membranes in Toad Bladder Epithelial Cells

In freeze-fracture (FF) preparations of ADH-stimulated toad urinary bladder, characteristic intramembrane particle (IMP) aggregates are seen on the protoplasmic (P) face of the luminal membrane of granular cells while complementary parallel grooves are found on the exoplasmic (E) face . These IMP aggregates specifically correlate with ADH-induced changes in water permeability . Tubular cytoplasmic structures whose membranes contain IMP aggregates which look identical to the IMP aggregates in the luminal membrane have also been described in granular cells from unstimulated and ADH-stimulated bladders . The diameter of these cytoplasmic structures (0.11 ± 0.004 ,um) corresponds to that of tubular invaginations of the luminal membrane seen in thin sections of ADH-treated bladders (0.13 ± 0.005 pm). Continuity between the membranes of these cytoplasmic structures (which are not granules) and the luminal membrane has been directly observed in favorable cross-fractures . In FF preparations of the luminal membrane, these apparent fusion events are seen as round, ice-filled invaginations (0.13 ± 0.01 ,um Diam), of which about half have the characteristic ADHassociated aggregates near the point of membrane fusion . They are less numerous than, but linearly related to, the number of aggregates counted in the same preparations (n = 78, r = 0.71, P < 0.01) . These observations suggest that the IMP aggregates seen in luminal membrane after ADH stimulation are transferred preformed by fusion of cytoplasmic with luminal membrane . Freeze-fracture electron microscopy has shown that stimulation ofthe isolated amphibian urinary bladder with antidiuretic hormone (ADH) results in a structural change in the luminal membrane of granular epithelial cells (1, 3, 11, 12) . Whereas in the unstimulated bladder intramembrane particles (IMP) are randomly distributed in an apparently J. CELL BIOLOGY0The Rockefeller University Press 0021-9525/80/04/0083/13 $1.00 Volume 85 April 1980 83-95 homogeneous matrix, after ADH stimulation IMP aggregates of various sizes are seen at discrete membrane sites on the protoplasmic half-membrane (fracture face P) . Complementary areas of the apposed exoplasmic half-membrane (fracture face E) exhibit parallel rows of depressions (grooves), reflecting the linear organization ofpar83 on Jne 8, 2017 D ow nladed fom Published April 1, 1980