Influence of membrane heterogeneity on kinetics of nonelectrolyte tracer flows

Li, J. H.; Essig, Alvin

doi:10.1007/bf01868965

Cited by 8 publications

(6 citation statements)

References 15 publications

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“…The calculations presented suggest that, in some cases, the additional term still permits the assignment of the epithelial coefficients within a narrow range. The intuitive description of solute fluxes across a heteroporous membrane has already been given in discussions of anomalous solvent drag (Ussing and Johansen, 1969;Patlak and Rapoport, 1971) and isotope interaction (Li and Essig, 1976). The present work provides an extension to electrolyte fluxes in the context of proximal tubule transport .…”

Section: Model Parametersmentioning

confidence: 80%

“…The crucial feature of the model was the existence of two parallel pathways with different reflection coefficients for the important solutes, i.e ., a "heteroporous" structure. Subsequent work has identified the impact of epithelial heteroporosity on unidirectional tracer fluxes and the relation between tracer and bulk solute permeability coefficients (Li and Essig, 1976 ;Caplan and Essig, 1983). Convective paracellular solute flux has also been suspected in certain experiments with leaky epithelia (Berry and Boulpaep, 1975 ;Munck and Rasmussen, 1977 ;Bomsztyk and Wright, 1986).…”

Section: Introductionmentioning

confidence: 99%

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Convective paracellular solute flux. A source of ion-ion interaction in the epithelial transport equations.

Weinstein¹

1987

The Journal of General Physiology

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An electrolyte model of an epithelium (a cell and a tightjunction in parallel, both in series with a lateral interspace basement membrane) is analyzed using the formalism of nonequilibrium thermodynamics . It is shown that if the parallel structures are heteroporous (i .e ., reflection coefficients for two ion species differ between the components), then a cross-term will appear in the overall transport equations of the epithelium . Formally, this cross-term represents an ion-ion interaction . With respect to the rat proximal tubule, data indicating epithelial ionic reflection coefficients less than unity, together with the assumption of no transcellular solvent drag, imply the presence of convective paracellular solute flux . This means that a model applicable to a heteroporous structure must be used to represent the tubule, and, in particular, the crossterms for ion-ion interaction must also be evaluated in permeability determinations. A series of calculations is presented that permits the estimation of the Na-Cl interaction for rat proximal tubule from available experimental data . One consequence of tubule heteroporosity is that an electrical potential may be substantially less effective than an equivalent concentration gradient in driving reabsorptive ion fluxes .

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Section: Model Parametersmentioning

confidence: 80%

Section: Introductionmentioning

confidence: 99%

Convective paracellular solute flux. A source of ion-ion interaction in the epithelial transport equations.

Weinstein¹

1987

The Journal of General Physiology

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“…The experimental coefficients 4 UT, Lp, and c4 for sucrose transport across Cuprophan have recently been reported (6). At the three concentrations studied (c, = 150, 450, and 900 mM), Wcp exceeded UT.…”

Section: Discussionmentioning

confidence: 94%

“…This is strictly forbidden by Eqs. 4 and 17, but it is possible to show that a path can exist whose hydraulic conductivity is positive, whose reflection coefficient is zero, and whose tracer permeability is arbitrarily small. The contribution of such a path to the sums in Eq.…”

Section: Appendix Cmentioning

confidence: 99%

Transport across homoporous and heteroporous membranes in nonideal, nondilute solutions. II. Inequality of phenomenological and tracer solute permeabilities

Friedman¹,

Meyer²

1981

Biophysical Journal

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The phenomenological solute permeability (omega p) of a membrane measures the flux of solute across it when the concentrations of the solutions on the two sides of the membrane differ. The relationship between omega p and the the conventionally measured tracer permeability (omega T) is examined for homoporous and heteroporous (parallel path) membranes in nonideal, nondilute solutions and in the presence of boundary layers. In general, omega p and omega T are not equal; therefore, predictions of transmembrane solute flux based on omega T are always subject to error. For a homoporous membrane, the two permeabilities become equal as the solutions become ideal and dilute. For heteroporous membranes, omega p is always greater than omega T. An upper bound on omega p- omega T is derived to provide an estimate of the maximum error in predicted solute flux. This bound is also used to show that the difference between omega P and omega T demonstrated earlier for the sucrose-Cuprophan system can be explained if the membrane is heteroporous. The expressions for omega P developed here support the use of a modified osmotic driving force to describe membrane transport in nonideal, nondilute solutions.

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“…A third point of interest is the trans stimulation predicted by the unidirectional flux equations (14) and (16). This is illustrated in Fig.…”

Section: Discussionmentioning

confidence: 99%

Concentrationo-dependence of nonelectrolyte permeability of toad bladder

Chen

Walser

1979

J. Membrain Biol.

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A theoretical formulation was derived for the dependence of bulk solute permeability, P, defined as net flux divided by concentration gradient, delta c, across any membrane in which solute concentration is controlling for net flux, delta J. According to this formulation, delta J is stimulated by increments in trans concentration, c2, in the range c2/c1 equals 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 divided by tracer concentration, will be independent of c provided that P equals P, but will diminish with increasing c if P/P less than 1.P/P was not significantly different from unity for urea, and both P and P were independent of c 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 also P) of these two solutes, measured as c 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.

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Influence of membrane heterogeneity on kinetics of nonelectrolyte tracer flows

Cited by 8 publications

References 15 publications

Convective paracellular solute flux. A source of ion-ion interaction in the epithelial transport equations.

Convective paracellular solute flux. A source of ion-ion interaction in the epithelial transport equations.

Transport across homoporous and heteroporous membranes in nonideal, nondilute solutions. II. Inequality of phenomenological and tracer solute permeabilities

Concentrationo-dependence of nonelectrolyte permeability of toad bladder

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