Antidiuretic response in the urinary bladder of Xenopus laevis: Presence of typical aggrephores and apical aggregates (original) (raw)
Related papers
The Journal of Membrane Biology, 1973
A new method was devised to study the movement of water across the toad urinary bladder. The uptake of tritiated water (THO) into the tissue and serosal fluid of everted bladder sacs was compared with the appearance, over very short time periods (5 to 40 sec), of THO in the serosal fluid alone. The results showed that under basal conditions no significant difference could be detected between the specific radioactivity in the serosal fluid and the specific radioactivity in the tissue. In the presence of oxytocin the specific radioactivity in the bladder tissue in 5 sec was about 10 times the specific radioactivity present in the serosal fluid. The accumulation of tritiated water in the tissue under the action of oxytocin suggests the existence of a second barrier to water movement other than the luminal border. While the overall increase in permeability of the bladder wall by oxytocin is only about twice the control value, the increase in water uptake by the tissue is much higher. It is concluded that the increase in diffusion of water induced by oxytocin across the luminal border of the cells has been largely underestimated by previous determinations and would be large enough to explain the observed osmotic flux in similar conditions. It was also observed that the permeability of the bladder to water was a function of the tonicity of the mucosal solution. * Career investigator from the "Consejo Nacional de Investigaciones Cientfficas y T6cnicas" (CONICET), Argentina.
Biology of the Cell, 1989
In the amphibian urinary bltadder, water permeability is correlated with the insertion of intramembrane particle aggregates (IMPAs) into the apical plasma membrane (AM) of the granular cells. These aggregates are believed to contain water channels. Characterization of the IMPAs by comparing AM fractions of antidiuretic hormone (ADH)-treated and resting epithelia requires isolation and purification of AM-rich material, free of other cytoplasmic aggregate-containing organeHes, in both cases. A technique derived from freeze-fracture was chosen to isolate large sheets of apical membrane material from frog (Rana esculenta) urinary bladder epithelium. The apical side was plated on a polylysine-coated glass slide, frozen with liquid nitrogen, and fractured. A nylon mesh was inserted between the glass slide and the bladder, in order to bring the fracture plane back to the AM periodically. Fluorescent markers were used to characterize the material having fractured with the glass slide. Samples were observed by fluorescence and phase contrast microscopy. We obtained evidence that numerous patches of fractured AM remained on the glass surface without nuclei. A phase contrast picture was obtained only at a high magnification, indicating a low thickness of the recovered material. Further characterization was made with SDS-PAGE. Protein contents of samples were extracted under various experimental conditions and the patterns of ADH.treated, resting AM samples, or whole epithelial cell crude homogenates, were compared. Staining of some bands increased under certain conditions, whereas many others disappeared. Both morphological and biochemical approaches demonstrate that the recovered material was apical in origin. epithelial cells --amphibian urinary bladder --. apical membrane isolation ---freeze-fracture --antidiuretic hormone
Surface hydrophobicity and water transport of the toad urinary bladder: Effects of vasopressin
The Journal of Membrane Biology, 1988
The present study investigated whether the hydrophobic properties (wettability) of the luminal surface of the toad urinary bladder might play a role in modulating water transport across this epithelium. In the absence of vasopressin (ADH), water transport across the tissue was low, while luminal surface hydrophobicity (water contact angle) was relatively high. Following stimulation by ADH, water transport increased and surface hydrophobicity decreased. The addition of indomethacin to inhibit ADH-induced prostaglandin synthesis did not reduce these actions of ADH. In an attempt to alter water transport in this tissue, a liposomal suspension of surface-active phospholipids was administered to the luminal surface. This addition had no detectable influence on the low basal rates of water transport, but blocked the ADH-induced stimulation of water transport. We suggest that surface-active phospholipids on the toad bladder luminal membrane may contribute to the hydrophobic characteristics of this tissue. ADH may act to decrease surface hydrophobicity, facilitating the movement of water molecules across an otherwise impermeable epithelium. This surface alteration may be associated with the appearance of water channels in the apical membrane.
Urea uptake and translocation in toad urinary bladder: The effect of antidiuretic hormone
The Journal of Membrane Biology, 1977
The uptake of C14-urea into everted and noneverted bladder sacs was compared, over short time periods (up to 2 min), with the transepithelial urea fluxes. This method allowed the study of the time course of urea uptake and distribution, while previously this problem was only studied in steady-state conditions. When mucosal uptake was studied no accumulation of C14-urea inside the tissue was observed, indicating that the mucosal border could be the limiting step. Comparative studies of urea and inulin uptake from the serosal side showed that urea equilibrated with the water epithelial cells in less than 30 sec. This accumulation suggested again that the mucosal border is an effective barrier for urea translocation. The kinetics of the increase in urea permeability induced by antidiuretic hormone was also studied and it was similar (T1/2:4.3 min) to the kinetics of the increase in water permeability induced by the hormone (T 1/2 : 5.6 min). A strong parallelism was also observed between the time course of the increases in water and urea permeabilities induced by medium hypertonicity (T 1/2 25 and 26 min, respectively). The values obtained for the permeability coefficient ktrans), either at rest or under ADH were similar to those previously reported employing steady-state techniques (28+8 and 432 _+ 25 cm. sec-1.10-7, respectively). The mechanism of urea reabsorption by the renal tubule is a problem of major interest which has been widely investigated (see Schmidt-Nielsen, 1970). The toad urinary bladder, a tissue that resembles the mammalian renal tubule in several respects, has been largely used to study this problem. The observation that urea movement across toad bladder accelerated in the direction of net water flux (Leaf & Hays, 1962) suggested that urea translocated through true aqueous channels existing in the membrane, large enough to permit water-solute interactions. However, more recent observations demonstrated that the solvent drag effect on amide diffusion is abolished when the bathing solutions are effectively stirred
Cell and Tissue Research, 1974
The role of the tight junction in the hydrosmotic response of the frog urinary bladder has been analysed by comparative kinetic studies and freeze etching examination. The comparison of the time course of the variations in transepithelial water net flux and of the alterations of tight junction ultrastructure in bladders exposed to mueosal hyperosmolar solutions shows that blisters are present in the tight junction before any increase in transepithelial water net flux. This indicates that the two phenomena are dissociated. In the same experimental conditions, freeze etching examination shows the presence in the tight junction of large areas of smooth and apparently stretched membrane where the typical network structure has disappeared. These alterations are reduced by further treatment with oxytocin and are probably not involved in the physiological hydrosomotic response.