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  • 1975-1979  (5)
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  • 1
    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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    Paper (German National Licenses)
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  • 2
    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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  • 3
    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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  • 4
    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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  • 5
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    Effect of metabolic inhibitors on vasopressin-stimulated transport systems in the toad bladder (1979)
    Wiley
    Details
    Publication Date: 1979-01-01
    Print ISSN: 0091-7419
    Electronic ISSN: 1547-9366
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Published by Wiley
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