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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 65 (1982), S. 197-204 
    ISSN: 1432-1424
    Keywords: presteady-state fluxes ; cornea ; endothelium ; cellular and paracellular pathways ; net flux
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Instead of the conventional steady-state fluxes, the presteady-state fluxes of22Na across the rabbit corneal endothelium were measured. In contrast to reports that there is no net Na+ movement across the corneal endothelium, we find a net transport of Na+ across this tissue. The direction of net Na+ flux is from the stromal to the aqueous side and the magnitude is 2.3±0.4 μeq/cm2·hr (n=11,sem). Net Na+ transport is inhibited in the presence of ouabain (10−4 m). Acetazolamide (10−4 m) has only a slight inhibitory effect on the rate of Na+ transport but decreases the transendothelial potential difference by about 30%. The passive component of the Na+ transport has been estimated by analyzing the presteady-state influx and efflux curves and found to occur 10% via cellular and 90% via paracellular routes. The analysis for the separation of the pathways has been based on a recently proposed theory which holds that the flux ratio, regardless of its driving forces, is independent of time.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 73 (1983), S. 95-102 
    ISSN: 1432-1424
    Keywords: dilution potential ; biionic potential ; permeability ratios ; constant field equation ; electrogenic transport ; rabbit corneal endothelium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary We have measured the dilution and biionic potentials across the isolated rabbit corneal endothelium in order to learn about the ionic selectivity of its intercellular junctions. Single-salt dilution potentials have been measured as a function of [NaCl] or [NaHCO3] gradients across the tissue. Biionic potentials were similarly measured by replacing Na+ with K+ on either side of the tissue. The potentials thus measured were fit to the constant field equation and to an approximation of it to obtain the ionic permeabilities for K+, HCO 3 − and Cl− relative to Na+. The permeability sequence obtained wasP K〉P Na〉P HCO3≅P Cl. Potentials were also measured after imposing an osmotic gradient across the preparation using sucrose. The results obtained with all these methods are consistent and suggest that this tissue is slightly more permeant to cations than anions, but that the selectivity of the intercellular junction is relatively low. From these experiments, a 30mm gradient of salt across the endothelial layer would be needed in order to explain the observed spontaneous potential difference (about 1 mV, aqueous negative) across that layer if the potential was due to the selectivity of the intercellular junctions. Such a value for the gradient is much larger than theoretical estimates of it; therefore, we favor electrogenic transport of HCO 3 − as a better explanation for the origin of the spontaneous potential difference.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 86 (1985), S. 99-104 
    ISSN: 1432-1424
    Keywords: flux ratio ; frog skin ; isotopes ; sodium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary A method is described that makes it possible to separate the sodium fluxes through the isolated frog skin into sets characteristic of the cellular and the paracellular pathway, respectively. If there are two significant pathways for the ion, and if they differ with respect to flux ratio as well as mean passage time, the flux ratios for the individual pathways can be obtained from a set of inward and outward tracer fluxes, covering the time from the addition of the tracers until the achievement of constant fluxes in both directions.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1791-1807 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetic parameters associated with the thermal decomposition of native collagen have been obtained by thermogravimetric techniques. In order to achieve this a thermogravimetric analysis was carried out in the temperature range of 25°C to about 1000°C. In this temperature range, it had been found that the differential primary weight loss curve had yielded three distinct peaks for the tendon collagen. The thermal decomposition corresponding to each peak was analyzed to retrieve its kinetic parameters. The peak temperature associated with the first peak decreased as the water content in a sample increased, while that of the second peak was independent of its hydration condition. It is believed that the first and the second peaks are, respectively, results of: (1) dissociation of water from collagen, and (2) of breaking of the collagen molecule itself. The third peak has not been easily identified so far. The activation energy and the order of water decomposition are obtained by various known methods. The results obtained by these different approaches agree reasonably well. The kinetic parameters of second and third peak are also obtained and reported here.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Publication Date: 1976-09-01
    Print ISSN: 0005-2787
    Electronic ISSN: 1879-3002
    Topics: Biology
    Published by Elsevier
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  • 6
    Publication Date: 1976-09-01
    Print ISSN: 0005-2736
    Electronic ISSN: 1879-2642
    Topics: Biology , Chemistry and Pharmacology , Medicine , Physics
    Published by Elsevier
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