Apical cytoplasm

About: Apical cytoplasm is a research topic. Over the lifetime, 1080 publications have been published within this topic receiving 36131 citations.

Dynamics of apical membrane responses to ADH in amphibian bladder

Abstract: The dynamic insertion and retrieval of membrane at the apical surface plays an important role in the action of antidiuretic hormone (ADH). The addition of membrane with water channels is a crucial event in initiating the water permeability response. ADH-stimulated bladders display distinctive differentiations in the apical membrane that represent sites where intracellular vesicles carrying intramembrane particle aggregates have fused with the apical surface. In the absence of an osmotic gradient these fusion sites appear to be relatively stable structures, but in the presence of an osmotic gradient there seems to be continuous addition and retrieval of membrane during sustained exposure to ADH. It is now clear that a dynamic feedback process is present, such that the water permeability of the apical membrane is adjusted by retrieval or addition of membrane depending on the magnitude of the transepithelial osmotic gradient. Removal of ADH leads to a striking retrieval of apical membrane, and intact aggregates have been demonstrated in the membrane of the vesicles that form in the apical cytoplasm after reversal of the response. Structure-function analysis has provided unique information, demonstrating that membrane dynamics is central to the mechanism whereby ADH regulates osmotic permeability in the toad urinary bladder.

Involvement of cathepsins B and H in lysosomal degradation of horseradish peroxidase endocytosed by the proximal tubule cells of the rat kidney: II. Immunocytochemical studies using protein A-gold technique applied to conventional and serial sections.

Abstract: Immunoelectron microscopic localizations of cathepsins B and H and injected horseradish peroxidase (HRP) in the lysosomal system of rat kidney proximal tubules were investigated by a protein A-gold technique. Kidneys were fixed by perfusion at fixed intervals after intravenous injection of HRP. At 5 to 15 minutes after the injection, the endocytic apparatus--including the apical vesicles, tubules, and vacuoles (endosomes)--were stained for HRP, but they were negative for cathepsins. Within 15 to 30 minutes after the HRP injection, HRP-containing endosomes were fusing with preexisting lysosomes. In the S1 segment, they accumulated in the apical cytoplasm and formed giant phagosomes, which increased markedly in number and size after 1 hour. These phagosomes were composed of a peripheral clear matrix and electron-dense inclusions. The clear matrix was stained heavily for cathepsins and HRP, whereas the electron-dense inclusions were consistently negative for cathepsins and HRP. The same results also were obtained after the double-labeling and serial sectioning techniques. The dense inclusions were fragmented gradually as the phagosomes decreased in size. After 3 hours, the size and number of phagosomes returned to their normal state (before the HRP injection). These results indicate that the endocytic apparatus of the proximal tubule cells does not contain cathepsins. Phagosomes are formed by the fusion of endosomes containing the internalized protein with the preexisting lysosomes. The degradation of HRP in giant phagosomes occurred rapidly. The coexistence of cathepsins B and H with the endocytosed HRP suggests that these cystein proteinases are involved in the degradation of protein in heterophagosomes of the proximal tubule cells.

Glycoproteins in rabbit uterus during implantation. Differential localization visualized using 3H-N-acetyl-glucosamine labelling and FITC-conjugated lectins.

Abstract: The synthesis of glycoproteins in rabbit uterine epithelium during the late preimplantation period was studied using tritiated N-acetylglucosamine. In vivo labelling was achieved by the intra-uterine implantation of agar gel columns containing the precursor. Autoradiography showed the radioactivity to be predominantly localized in the apical cell surfaces, with single cells exhibiting an accumulation of silver grains in their supranuclear cytoplasm. After gel electrophoresis of uterine flushings, activity was mainly found in the β-glycoprotein fraction. Fluorescein isothiocyanate (FITC)-conjugated wheat-germ agglutinin reacted with the apical cytoplasm and surfaces of the endometrial cells. However, FITC-conjugated concanavalin A exhibited a different binding pattern, reacting first with the basal cytoplasm, and later with the apical cytoplasm. After concanavalin-A staining, single cells exhibited positive vesicles in their lateral and apical parts. These cells may be released into the uterine lumen until 210 h post coitum. Neither of the lectins reacted with ciliated cells. Concanavalin A showed an affinity for the β-glycoprotein fraction of the uterine secretion. The results indicate that, although all endometrial cells contain glycoproteins, only a few of these seem to be involved in the synthesis of secretory products.

Occurrence and Ultrastructure of Collar Cells in the Stomach Gastrodermis of Polypodium hydriforme Ussov (Cnidaria)

Abstract: The existence of collar cells lining the stomach gastrodermis in free-living Polypodium hydriforme and their ultrastructure are described. The collar cells are provided with a collar consisting of 9–10 microvilli which encircles a central flagellum and forms a flagellar pit. At the bottom of the pit around the basal part of the flagellum there is fine crystalline material which extends also in the spaces between the microvilli and keeps them straight. The flagellum has a typical axoneme (9+2), its basal body is located below the apical surface of the collar cell and continues into a striated rootlet. An accessory centriole is situated close to the upper part of the rootlet. The cell nucleus is located in the basal part of the cell. Prominent mitochondria with tubular cristae, Golgi cisternae and fragments of rough endoplasmic reticulum are situated mostly in the basal part of the cytoplasm. Discoidal vesicles are abundant in the apical cytoplasm. The collar cells are connected to each other by septate junctions and interdigitations. The ultrastructure of collar cells described here is discussed in comparison to that of other Cnidarians and in connection with the problem of Polypodium's systematic position.

An X-ray microanalytical study on the effects of ouabain and N-ethyl maleimide on the elemental concentrations in Malpighian tubule cells of Locusta.

Abstract: X-ray microanalysis was used to study elemental distribution in Malpighian tubule cells of Locusta migratoria and how these are affected by the replacement of bathing medium K+ with Rb+ and by inclusion of the transport inhibitors ouabain and n-ethyl maleimide (NEM) in standard (K+-containing) and Rb+-Ringer (K+-free) solutions. Incubation of tubules in standard Ringer containing 1mM ouabain dramatically affected the intracellular levels of K and Na. The intracellular K concentration fell and Na concentration increased in all regions studied. Despite this, a gradient of increasing K concentration from basal to apical cell surface was maintained. Ouabain also reduced the intracellular levels of Rb when applied in Rb+-Ringer. Cl and P levels were unaffected by ouabain treatment. Incubation in standard and Rb+-Ringer solutions containing 1 microM NEM caused a significant increase in intracellular K levels in all regions of the cell compared with that observed in the absence of NEM. Rb levels were little affected by NEM except in the apical cytoplasm and microvillar regions where they were significantly reduced compared with Rb+-Ringer controls. NEM effected a significant increase in cellular levels of Na under Rb+-Ringer conditions. Intracellular Cl and P were not significantly affected by NEM. These results are discussed in relation to proposed mechanisms for the transport of ions and water across this secretory epithelium, with particular emphasis on the role of K+ as the 'prime mover' in this process.