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  • 1
    Electronic Resource
    Electronic Resource
    The effect of tanning agents on the permeability of the toad bladder to water and solutes (1973)
    Springer
    The journal of membrane biology 14 (1973), S. 177-191 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Previous studies with phloretin have shown that the movement of urea and other solutes across the toad bladder can be inhitited with no effect on osmotic water flow, active sodium transport, or the movement of ethanol and ethylene glycol. These findings have suggested that a vasopressin-sensitive carrier is involved in the transport of solutes such as urea across the luminal membrane of the epithelial cell. The present paper describes the effect of two agents other than phloretin: tannic acid and chromate, on water and solute movement across the bladder. The pattern of action of these two agents resembles that of phloretin, and supports our earlier findings of the independence of solute and water movement. The effect of chromate on urea movement is seen only in the presence of vasopressin, and only if chromate is added prior to vasopressin. Chromate also proves to be an irreversible inhibitor of urea movement. The implications of these findings are discussed. In view of the known interactions of both agents with proteins, it is suggested that carrier-mediated transport of urea proceeds across a protein component of the membrane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01868076
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  • 2
    Electronic Resource
    Electronic Resource
    The role of water diffusion in the action of vasopressin (1970)
    Springer
    The journal of membrane biology 2 (1970), S. 263-276 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Vasopressin produces a large increase in the osmotic flow of water across the toad bladder, with little apparent change in the diffusion rate of tritiated water. This discrepancy between osmotic and diffusional net flow is the basis of the pore theory of vasopressin action. The present studies show that there is in fact a large (at least 10-fold) increase in water diffusion subsequent to addition of vasopressin, which is masked by unstirred layers and by the resistance offered to diffusion by the thick layer of connective tissue and muscle supporting the bladder epithelial cells. An even higher diffusion rate would be anticipated with the complete elimination of unstirred layers, and of barriers to diffusion remaining within the epithelial layer itself. An alternative to the pore hypothesis is considered, in which vasopressin acts solely by increasing the diffusion rate of water across the luminal membrane of the epithelial cell.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01869864
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  • 3
    Electronic Resource
    Electronic Resource
    Independent pathways for water and solute movement across the cell membrane (1972)
    Springer
    The journal of membrane biology 10 (1972), S. 367-371 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary In published studies of the relationship between movement of nonelectrolytes across cell membranes and the lipid solubility of these test molecules, it is generally found that a number of the smaller, more water-soluble molecules deviate significantly from the general pattern relating permeability (or reflection coefficient) to lipid solubility. This is often true of the amides, for example, whose reflection coefficients are considerably lower than expected on the basis of lipid solubility. While this has been interpretep in terms of the movement of these solutes through aqueous channels in the membrane, it now appears that many of these “deviant” molecules may cross the membrane by means of carrier-mediated diffusion, independent of osmotic water flow. This has important implications for studies in which equivalent pore radius has been estimated from the reflection coefficients of small hydrophilic molecules, and for our present concepts of membrane structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01867867
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  • 4
    Electronic Resource
    Electronic Resource
    Selective inhibition of urea transport by oxidizing agents (1975)
    Springer
    The journal of membrane biology 25 (1975), S. 327-339 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Urea and water transport across the toad bladder epithelial cell appears to take place through independent vasopressin-stimulated pathways. Agents such as chromate, for example, when added to the luminal bathing medium, inhibit urea transport without inhibiting osmotic water flow, providing evidence for such independent pathways. In the present study, selective inhibition of urea transport is shown for permanganate and methylene blue, which, like chromate, are oxidizing agents. Permanganate inhibits urea transport irreversibly, while methylene blue acts reversibly. Not all oxidizing agents are inhibitory; perchlorate, peroxide and ferricyanide have no effect on urea transport or water flow. Permanganate and chromate both act at a point beyond the generation of cyclic AMP, since they continue to inhibit urea transport in bladders treated with exogenous cyclic AMP, 8-bromoadenosine 3′,5′-cyclic monophosphate, and a combination of cyclic AMP and theophylline. These findings suggest that selective inhibition of urea transport can be brought about by oxidation of one or more components in its transport pathway, and that, in the case of chromate and permanganate, these components may be in the luminal membrane itself.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01868582
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  • 5
    Electronic Resource
    Electronic Resource
    Membrane proteins and urea and acetamide transport in the human erythrocyte (1975)
    Springer
    The journal of membrane biology 20 (1975), S. 181-190 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Previous studies have shown that urea and acetamide traverse the erythrocyte membrane by way of facilitated diffusion. The nature of this selective pathway is unknown. The present studies investigate the effects of proteolytic enzymes and crosslinking agents on amide transport. Cleavage of the erythrocyte membrane surface by pronase or trypsin had no effect on urea and acetamide permeability or inhibition by phloretin. These findings suggest that the sialoglycopeptide segment of the sialoglycoproteins is not critical to urea and acetamide transport. In addition, extensive crosslinking of membrane proteins with glutaraldehyde had no effect on amide transport in the absence or presence of phloretin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01870635
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  • 6
    Electronic Resource
    Electronic Resource
    Membrane pathways for water and solutes in the toad bladder: II. Reflection coefficients of the water and solute channels (1979)
    Springer
    The journal of membrane biology 49 (1979), S. 269-281 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Urea and water transport across the toad bladder can be separately activated by low concentrations of vasopressin or 8 Br-cAMP. Employing this method of selective activation, we have determined the reflection coefficient (σ) of urea and other small molecules under circumstances in which the bladder was transporting urea or water. An osmotic method for the determination of σ was used, in which the ability of a given solute to retard water efflux from the bladder was compared to that of raffinose (σ=1.0) or water (σ=0). When urea transport was activated (low concentration of vasopressin), σ for urea and other solutes was low, (σurea,0.08–0.39;σacetamide, 0.55; σethylene glycol, 0.60). When water transport was activated (0.1mm 8 Br-cAMP) σurea approached 1.0 σurea also approached 1.0 at high vasopressin concentrations. In a separate series of studies, σurea was determined in the presence of 2×10−5 m KMnO4 in the luminal bathing medium. Under these conditions, when urea transport is selectively blocked, σurea rose from a value of 0.12 to 0.89. Thus, permanganate appears to “close” the urea transport channel. These findings indicate that the luminal membrane channels for water and solutes differ significantly in their dimensions. The solute channels, limited in number, have relatively large radii. They carry a small fraction (approximately 10%) of total water flow. The water transport channels, on the other hand, have small radii, approximately the size of a water molecule, and exclude solutes as small as urea.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01871122
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  • 7
    Electronic Resource
    Electronic Resource
    Membrane pathways for water and solutes in the toad bladder: I. Independent activation of water and urea transport (1979)
    Springer
    The journal of membrane biology 49 (1979), S. 253-268 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Vasopressin activates a number of transport systems in the toad bladder, including the systems for water, urea, sodium, and other small solutes. Evidence from experiments with selective inhibitors indicates that these transport systems are to a large extent functionally independent. In the present study, we show that the transport systems can be separately activated. Low concentrations of vasopressin (1 mU/ml) activate urea transport with virtually no effect on water transport. This selective effect is due in part to the relatively greater inhibitory action of endogenous prostaglandins on water transport. Low concentrations of 8-bromoadenosine cyclic AMP, on the other hand, activate water, but not urea transport. In additional experiments, we found that varying the ratio of exogenous cyclic AMP to theophylline activated water or urea transport selectively. These studies support the concept of independently controlled systems for water and solute transport, and provide a basis for the study of individual luminal membrane pathways for water and solutes in the accompanying paper.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01871121
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  • 8
    Electronic Resource
    Electronic Resource
    Fusion images and intramembrane particle aggregates during the action of antidiuretic hormone (1985)
    Springer
    Cell & tissue research 240 (1985), S. 433-439 
    Details
    ISSN: 1432-0878
    Keywords: Antidiuretic hormone ; Freeze-fracture ; Rapid-freeze ; Fusion events ; Particle aggregate turnover ; Urinary bladder ; Anura
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Antidiuretic hormone (ADH) causes the appearance of water-conducting particle aggregates in the luminal membrane of receptor cells in amphibian bladder and skin, and in the mammalian collecting duct. The aggregates originate from cytoplasmic tubules that fuse with the luminal membrane during ADH stimulation. We have studied the process of fusion and the structure of the particle aggregates by a rapid-freeze technique that renders chemical fixation and glycerol protection unnecessary. Our findings differ in some important respects from previously published work. Aggregate particles, in our study, partition equally between the external (EF) and protoplasmic (PF) membrane leaflets, rather than remaining in the protoplasmic leaflet exlcusively. By including the entire population of fusion images in our survey, we have found that aggregate delivery in ADH-treated cells proceeds preferentially from small fusion images whose diameter is significantly less than the 0.12 μm characteristic of the carrier tubules themselves. We have also found that, even in unstimulated preparations, fusion images are numerous, being mostly of small diameter. ADH stimulation produces a moderate increase in the number of fusion images and a significant increase in fusion-image diameter. These findings indicate that the individual particles are mobile within the membrane, lacking interparticle linkage. In addition, contact of cytoplasmic tubules with the luminal membrane may take place even in the absence of ADH, producing small fusion images which are not associated with aggregate delivery to the luminal membrane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00222356
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  • 9
    Electronic Resource
    Electronic Resource
    Effect of metabolic inhibitors on vasopressin-stimulated transport systems in the toad bladder (1979)
    New York, N.Y. : Wiley-Blackwell
    Journal of Supramolecular Structure 10 (1979), S. 175-184 
    Details
    ISSN: 0091-7419
    Keywords: vasopressin ; nocodazole ; urea transport ; rotenone ; dinitrophenol ; methylene blue ; Life Sciences ; Molecular Cell Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Vasopressin increases the permeability of receptor cells to water and, in tissues such as toad bladder, to solutes such as urea. While cyclic AMP appears to play a major role in mediating the effects of vasopressin, there is evidence that activation of the water permeability system and the urea permeability system involves separate pathways. In the present study, we have shown that inhibitors of oxidative metabolism (rotenone, dinitrophenol, and methylene blue) selectively inhibit either vasopressin-stimulated water flow or vasopressin-stimulated urea transport. There was no inhibition, however, when exogenous cyclic AMP was substituted for vasopressin, and little to no inhibition when the potent analogue 8-bromoadenosine 3′,5′-cyclic monophosphate (8-Br-cAMP) was employed. Rotenone had no effect on adenylate cyclase activity or cyclic AMP levels within the cell; dinitrophenol decreased adenylate cyclase activity minimally.Additional studies with vinblastine and nocodazole, inhibitors of microtubule assembly, demonstrated an inhibition of vasopressin and cyclic AMP-stimulated water flow but showed no effect on urea transport.We would conclude that water and urea transport, as examples of hormone-stimulated processes, have different links to cell metabolism, and that in addition to cyclic AMP, a non-nucleotide pathway may be involved in the action of vasopressin.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jss.400100207
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  • 10
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    A Hepatocyte-Targeted Conjugate Capable of Delivering Biologically Active Colchicinein Vitro (1996)
    American Chemical Society
    Details
    Publication Date: 1996-01-01
    Print ISSN: 1043-1802
    Electronic ISSN: 1520-4812
    Topics: Chemistry and Pharmacology
    Published by American Chemical Society
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