Synthesis and transport studies of the intrasyncytial lamina: an unusual placental basement membrane in the little brown bat, Myotis lucifugus

The chorioallantoic placenta of Myotis lucifugus undergoes a transition from endotheliochorial to hemochorial. The original maternal endothelial basement membrane is incorporated into the apical portion of the syncytial trophoblast, where it persists until term. This intrasyncytial lamina is separated from the maternal blood by thin ectoplasmic projections of the syncytial trophoblast that project through the lamina and spread over the surface, completely engulfing it. While there appear to be direct channels, at junctions of the ectoplasmic processes, from the maternal blood to the intrasyncytial lamina, perfusion studies using the electron-dense tracers alcian blue, ruthenium red, and Thorotrast show that these channels are physiologically closed. In contrast, lanthanum nitrate was able to gain access to the lamina via the extracellular channels. The endocytic uptake of the tracers was similar. These studies suggest several pathways for substances to cross the ectoplasmic zone and the intrasyncytial lamina. Substances may gain direct access to the lamina via extracellular channels, reach the lamina by vesicular transport, or bypass the lamina completely through fenestrations within the lamina. Autoradiographic studies show that the syncytial trophoblast synthesizes portions of the intrasyncytial lamina, demonstrating its partial fetal origin. How long the original maternal components persist and the functional significance of the intrasyncytial lamina are unknown. Possible functions of the lamina include increased surface area of the apical plasmalemma, selective filtration, structural support, and maintenance of cell polarity.

Characterization and use of polyclonal antibody to Na+,K+-ATPase: immunocytochemical localization in salt glands of the duck

The amount of Na+,K+-ATPase of the avian salt gland increased concomitantly with plasma membrane surface area during salt feeding of ducklings (adaptation), and both enzyme content and membrane surface area decreased upon return to fresh water (deadaptation). In a further study of the enzyme, a marker for plasma membrane biogenesis, polyvalent antibodies were raised to the denatured alpha-subunit of the purified ATPase. Antisera did not inhibit enzymatic activity but immunoprecipitated the phosphorylated intermediate of the alpha-subunit. Furthermore, the alpha-subunit, which was not glycosylated, was immunoprecipitated from homogenates of tissue slices metabolically labelled with [35S]-methionine, using antisera raised against either duck salt gland or dog kidney alpha-subunit. The former antisera also recognized the alpha-subunit in the brain, heart, kidney, liver, intestine and skeletal muscle of the duck. Immunocytochemistry with the antisera raised to the duck salt gland alpha-subunit revealed reaction at basolateral as well as apical plasma membrane in the duck salt gland principal cells, with essentially no deposits on peripheral cells, fibroblasts, erythrocytes, endothelial cells and neural elements. Within the principal cells, immunolabelling was also detected on small vesicles, multivesicular bodies and lysosomes; deposits on extracellular debris and vesicles in the lateral and lumenal spaces were also apparent. The labelling patterns were qualitatively but not quantitatively similar in salt glands of control, adapted and deadapted ducklings, and are discussed in the context of a model for plasma membrane biogenesis and turnover in which degradative events may play a major role.