Ionic conductivity and local structural features in Ce1-xSmxO2-x/2.

Sm-Doped ceria is one of the most promising materials to be used as electrolyte in solid oxide fuel cells due to its remarkable ionic conductivity values in the intermediate temperature range. Transport properties and local structural features of Ce1-xSmxO2-x/2 (0.1 ≤ x ≤ 0.7) were studied by an impedance/µ-Raman spectroscopy coupled approach up to 1073 K. Results suggest that C-based nanosized defect clusters are responsible for the drop in ionic conductivity observed even at x = 0.2, i.e. at a Sm content lower than necessary to allow C domains to reach the percolation threshold through crystallites. Moreover, within the fluorite-type compositional region, with increasing the Sm content, defect clusters undergo a rearrangement resulting in the enlargement of C-based domains rather than in the increase of their number; at higher x, on the contrary, both the size and amount of C domains increase in parallel.

ADH and phorbol ester increase immunolabeling of the toad bladder apical membrane by antibodies made to granules.

Polyclonal antibodies were raised to isolated toad bladder granules. On immunoblots, the anti-granule antiserum specifically stained components of isolated granules. Immunocytochemically, the anti-granule antiserum labeled the apical surface of the bladder. Immunolabeling increased at the apical surface when the bladder was exposed to antidiuretic hormone (ADH) serosally or phorbol ester (PMA) mucosally--conditions which stimulate apical granule exocytosis. The increase in granule epitopes on the apical surface was sixfold greater than the net increase in surface area.

Isolation and characterization of granules of the toad bladder.

The electron-dense granules that lie just below the apical plasma membrane of granular epithelial cells of toad urinary bladder contribute glycoproteins to that apical membrane. Also, exocytosis of granules (and tubules) elicited by antidiuretic hormone potentially doubles that apical surface, during the same period the transport changes characteristic of the hormonal response occur. Granules separated from other membrane systems of the cells provide the material to assess the importance of the granules as glycocalyx precursors and in hormone action. We used isosmotic media to effect preliminary separations by differential centrifugation. Then granules were isolated by centrifugation on self-forming gradients of Percoll of decreasing hypertonicity. We find qualitative and quantitative changes in protein composition and enzymic activities in the isolated fractions. The primary criterion for granule purification was electron microscopic morphology. In addition, polypeptide species found in the granule fraction are limited in number and quantity. The granules are enzymically and morphologically not lysosomal in nature. Granules may provide the glycoproteins of the apical glycocalyx but they differ from the isolated plasma membrane fraction enzymically, in protein composition and in proportion of esterified cholesterol. We conclude that the granules are not "average" plasma membrane precursors. Their role in the membrane properties of the toad urinary bladder may now be evaluated by characterizing permeability and other properties of the isolated organelles.