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  • 1975-1979  (4)
Material
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Year
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 27 (1976), S. 381-391 
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Bidirectional sodium fluxes across toad bladder were measured after eliminating active transport with ouabain. Mucosal sodium concentration,C m , was progressively reduced (from 114 to 3mm) while serosal sodium remained constant. Potential difference was maintained at zero by current passage. The ratio,Q, of the bulk permeability coefficient for sodium,P, to the tracer sodium permeability coefficientP *, was found to remain constant asC m decreased. Equations were derived on this basis for bidirectional fluxes and forP andP * as functions ofC m , which corresponded closely to the observed data. The explanation for the observed value ofQ and its constancy under these conditions is uncertain.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 48 (1979), S. 21-42 
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary A theoretical formulation was derived for the dependence of bulk solute permeability,P, defined as net flux :- concentration gradient, Δc, across any membrane in which solute concentration is controlling for net flux, $$\mathop J\limits^\Delta $$ . According to this formulation, $$\mathop J\limits^\Delta $$ is stimulated by increments in trans concentration,c 2, in the rangec 2/c 1=0.0–0.1. Net flux of urea across toad bladder down concentration gradients was shown to be stimulated threefold by small increments in trans urea concentration. The theory also predicts that, in the absence of concentration gradients, tracer permeability,P *, defined as tracer flux :- tracer concentration, will be independent ofc provided thatP=P *, but will diminish with increasingc ifP/P *〈1.P/P * was not significantly different from unity for urea, and bothP andP * were independent ofc in the absence of concentration gradients. However,P/P * was significantly less than unity (0.90 and 0.85) for thiourea and mannitol, respectively. In conformity with theory,P * (and alsoP) of these two solutes, measured asc was increased by 3–4 orders of magnitude, diminished progressively. These effects are more consistent with this formulation than with transport via a saturable carrier.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 32 (1977), S. 319-330 
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Bidirectional sodium fluxes were measured across toad bladder sacs after eliminating active transport with ouabain. Transepithelial potential was clamped to 100 mV or the Nernst potential,ψ eq, at varying sodium concentrations,C m , in the mucosal medium. Serosal sodium concentration,C s , was held constant. Equations were derived for permeability, partial ionic conductance, and unidirectional fluxes as functions ofC m andC s , based in part on the assumption that the ratio,Q, of bulk sodium permeability to tracer sodium permeability is a constant, independent of concentration and potential. The results conformed closely to these equations.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 21 (1975), S. 87-98 
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary To assess the active components of sodium flux across toad bladder as a function of transepithelial potential, unidirectional sodium fluxes between identical media were measured before and after adding sufficient ouabain (1.89×10−3 m) to eliminate active transport, while clamping transepithelial potential to 0, 100 or 150 mV. Evidence was adduced that ouabain does not alter passive fluxes, and that fluxes remain constant if ouabain is not added. Hence, the ouabain-inhibitable fluxes represent fluxes through the active path. Results were analyzed by a set of equations, previously shown to describe adequately passive fluxes under electrical gradients in this tissue, here modified by the insertion ofE, the potential at which bidirectional sodium fluxes (β E and Φ E ) through the active pathway are equal. According to these equations, β E and Φ E are the logarithmic mean of bidirectional fluxes through the active path at any potential, and the flux ratio in this path is modified by a constant factorQ ia, which represents the ratio of the bulk diffusion coefficient to the tracer diffusion coefficient in this pathway. The data are shown to conform closely to these equations.Q ia averages 2.54. Hence, serosal-to-mucosal flux vanishes rapidly as potential falls belowE. MeanE in these experiments was 158±1 mV. Thus, linear dependence of net flux in both active and passive pathways on potential is present, even though the sodium fluxes in both paths fail to conform to the Ussing flux ratio equation.Q i p〈1 in the passive path (qualitatively similar to exchange diffusion) andQ ia〉1 in the active path (as in single file pore diffusion). Both of these features tend to reduce the change in serosal-to-mucosal sodium flux induced by depolarization from spontaneous potential to zero potential (“short-circuiting”).
    Type of Medium: Electronic Resource
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