Redistribution of surface macromolecules in dissociated epithelial cells.

A number of ultrastructural and cytochemical techniques were used to study intact epithelial cells lining the frog urinary bladder: high resolution autoradiography after administration of [3H]glucosamine or [3H]fucose; 125I iodination of external protein; concanavalin A-peroxidase, periodic acid-chromic acid silver methenamine; and colloidal thorium. Results indicate that the material (probably glycoprotein) coating the apical surface differs from that which lines the lateral and basal surfaces. After dissociation and isolation of the epithelial cells, the material previously confined to the apical surface invaded progressively the opened "tight junctions" (about 5 min), then the lateral membranes (about 40 min), and finally the basal membrane (about 80 min): at that time, the whole cell surface was entirely enveloped by the apical material. Since, on the one hand, the reacting material was confined to the apical surface when the tight junctions were closed (in intact epithelial cells) and since, on the other hand, the apical material was sliding down the laterobasal membranes when the tight junctions were opened (in dissociated cells), it may be concluded that tight junctions contribute to maintain the cell surface specialization in epithelia.

The host-parasite interface of strigeoid trematodes

A detailed study of the structure of the tegument of D. phoxini has been carried out using probe and transmission electron microscope. The distribution of spines and sense organs on the forebody has been described, as well as the nature of the lappets in the everted and retracted state. The adhesive organ exhibits two different surfaces which also differ from the surface of the rest of the body. The use of the ‘Stereoscan’ has confirmed and extended the concept of surface specialization based on transmission studies.

Studies on the host–parasite interface of strigeoid trematodes

The adhesive organ of Apatemon gracilis minor Yamaguti, 1933, consists of two lobes lying in a cup-shaped fore-body. The cytoplasmic tegument covering the apposing faces of the lobes is different from that covering their outer surfaces. The covering of the outer surface corresponds to the general tegument present on the rest of the body, whereas that on the inner surfaces is finely pitted and in certain regions is elevated to form a coarse reticulum. This specialized surface is covered externally by a plasma membrane and is in continuity with nucleated cell bodies lying below the basement layer. The cell bodies contain large quantities of granular endoplasmic reticulum as well as several Golgi complexes and numerous mitochondria. Masses of secretion bodies are present and these also occur in the extensions to the external tegument as well as within the external tegument of the lobes. When the parasite is attached the inner faces of the lobes come into contact with the vascular lamina propria of the host. The possible biological role of this specialized host–parasite interface is discussed and it is suggested that this surface specialization may form a morphological basis for the ‘placental’ function suggested for the adhesive organ by earlier workers.The author wishes to acknowledge the research grant provided by the S.R.C. for the purchase of a vacuum coating unit and an AEI EM 6 electron microscope. The progress of this study was greatly facilitated by the excellent assistance of Mr T. Davies and Miss C. Green. The Stereoscan micrographs are published by permission of the Cambridge Instrument Company.

THE DEVELOPMENT OF SURFACE SPECIALIZATION IN THE SECRETORY EPITHELIUM OF THE AVIAN SALT GLAND IN RESPONSE TO OSMOTIC STRESS

Cell surface specialization, a characteristic common to most ion-transporting epithelia, was studied in the salt (nasal) gland of the domestic duck in relation to osmotic stress. Three days after hatching, experimental ducklings were given 1% NaCl to drink for 12 hr and freshwater for the remainder of each day. Control ducklings were maintained exclusively on freshwater. The fine structure of the secretory epithelium was examined on various days of the regimen. The nasal gland epithelium of the secretory lobule is composed of several types of cells. Peripheral cells, lying at the blind ends of the branched secretory tubules, are similar in both control and experimental animals at all stages of glandular development. These generative cells contain few mitochondria and have nearly smooth cell surfaces. Partially specialized secretory cells predominate in the secretory tubules of control animals and appear as transitional cells in the tubular epithelium of salt-stressed animals. These cells contain few mitochondria and bear short folds along their lateral cell surfaces. Fully specialized cells dominate the secretory epithelium of osmotically stressed ducklings. The lateral and basal surfaces of these cells are deeply folded, forming complex intra- and extracellular compartments. This vast increase in absorptive surface area is paralleled by an increase in the number of mitochondria that pack the basal compartments. The development of this fully specialized cell is correlated with the marked increase in (Na+-K+)-ATPase activity in the glands of osmotically stressed birds.