Isotope Flows and Flux Ratios in Biological Membranes

Kedem, O.; Essig, Alvin

doi:10.1085/jgp.48.6.1047

Cited by 111 publications

(50 citation statements)

References 22 publications

(75 reference statements)

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“…This result is formally identical to that obtained by Kedem and Essig (1965), although it should be noted that the precise identification of the phenomenological coefficients will depend on the nature of the coupled processes and the presence or absence of parallel paths for transmural ion flow. Hoshiko and Lindley (1970) have stressed the need for macroscopic specification of ideal tracer behavior.…”

Section: J~i/pz A2 Rtsupporting

confidence: 82%

“…a phenomenological description of the relation between the flows and forces which interact to produce observable membrane transport phenomena. One particularly useful result of this work was the introduction by Kedem (1961) of a general expression which relates the net flow of some species, i, across a membrane to three classes of thermodynamic forces, i.e. :…”

Section: The Thermodynamic Approachmentioning

confidence: 99%

“…Integrating this ratio across the membrane for steady-state tracer flow, he obtained the well known result that, for simple diffusional flow, the tracer flux ratio depends only on the activities of tracer in the bathing solutions and the electrical potential difference across the membrane. More recently, several authors have examined in detail the theoretical foundations of the flux-ratio equation in an effort to clearly define the necessary assumptions about tracer movement, and to generalize the flux-ratio equation to include the effects of coupled processes and membrane inhomogeneity (Hoshiko & Lindley, 1964;Kedem & Essig, 1965;Schwartz, 1971). These treatments, however, also proceed from a local description of flows and forces to a global flux-ratio equation.…”

Section: The Flux Ratio For Simple Diffusionmentioning

confidence: 99%

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Tracer flux ratios: A phenomenological approach

Dawson

1977

J. Membrain Biol.

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The kinetic behavior of tracer flows across epithelial membranes is examined and attention is called to the condition under which unidirectional tracer flows may be described by first order rate equations. It is shown that the first order nature of the tracer rate equation when combined with simple thermodynamic constraints on tracer flow yields a relation between the ratio of the unidirectional rate coefficients and thermodynamic driving forces. The form of this relation is examined for the case of simple diffusion and in the presence of coupled process.

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Section: J~i/pz A2 Rtsupporting

confidence: 82%

Section: The Thermodynamic Approachmentioning

confidence: 99%

Section: The Flux Ratio For Simple Diffusionmentioning

confidence: 99%

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Tracer flux ratios: A phenomenological approach

Dawson

1977

J. Membrain Biol.

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“…Furthermore, the common use of the flux ratio to evaluate ENa requires the questionable assumption that the movements of abundant and tracer species of sodium ions in the active transport pathway are independent (Ussing, 1960). In any event equivalence of the values of ENa obtained by the above two techniques would require that the rate of metabolism be independent of the electrical potential difference across the membrane (Kedem and Essig, 1965;Blumenthal and Kedem, 1969).…”

Section: Introductionmentioning

confidence: 99%

Energetics of Sodium Transport in Frog Skin

Vieira

Caplan

Essig

1972

The Journal of General Physiology

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Studies were made of the dependence of the rate of oxygen consumption, J , on the electrical potential difference, A,, across the frog skin. After the abolition of sodium transport by ouabain the basal oxygen consumption was independent of /x. In fresh skins J, was a linear function of Alk over a range of at least --70 my. Treatment with aldosterone stimulated the shortcircuit current, Io, and the associated rate of oxygen consumption, Jro, and increased their stability; linearity was then demonstrable over a range of 4-160 mv. Brief perturbations of A4 (30-200 my) did not alter subsequent values of 10. Perturbations for 10 min or more produced a "memory" effect both with and without aldosterone: accelerating sodium transport by negative clamping lowered the subsequent value of I0; positive clamping induced the opposite effect. Changes in Jo were more readily detectable in the presence of aldosterone; these were in the same direction as the changes in I0. The linearity of J. in A& indicates the validity of analysis in terms of linear nonequilibrium thermodynamics-brief perturbations of A#p appear to produce no significant effect on either the phenomenological coefficients or the free energy of the metabolic driving reaction. Hence it is possible to evaluate this free energy.

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“…1 In the present study we utilize these techniques in membranes with minimal artefactual leakage to estimate the extent to which the enhancement of conductance by aldosterone is attributable to the active pathway. The data also permit an analysis of the utility of the flux ratio in evaluation of the "electromotive force of sodium transport," EN, [17,24,25].…”

mentioning

confidence: 99%

Effect of aldosterone on active and passive conductance andE Na in the toad bladder

Saito

Essig

1973

J. Membrain Biol.

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Summary. It has been demonstrated previously that aldosterone increases the electrical conductance of the toad bladder in association with the stimulation of active sodium transport. In the present study the concurrent measurement of electrical quantities and ion tracer flux distinguishes effects on active and passive pathways. Lack of an effect on passive Na + or CI-tracer flux in hemibladders preselected to eliminate large artefactual leaks indicates that aldosterone has no influence on physiological passive conductance. Thus, the enhancement of electrical conductance is entirely attributable to the active pathway. The magnitude of the increase in the active conductance was estimated. The data permitted also the comparison of effects on the flux ratio of Na + at short circuit (fo) and the electrical potential difference adequate to abolish active sodium transport (ENa). Even in membranes with minimal leakage the flux ratio does not reliably reflect ENa. Aldosterone increased mean fo from 11 to 22, but did not affect ENa.Active sodium transport across the toad bladder is believed to comprise two processes: (1) "passive" movement across the apical (mucosal) surface into the cell [13], followed by (2) "active" extrusion at the basal-lateral (serosal) surface [14]. Accordingly, in attempting to explain how aldosterone facilitates sodium transport, two main hypotheses have been advanced. Crabb6 [5] and Sharp and Leaf [21,22] have suggested that aldosterone increases mucosal permeability, permitting more rapid passive inflow and elevation of the intracellular sodium concentration, with resultant enhancement of active transport across the serosal surface. Edelman and his co-workers [12,20], on the other hand, have urged the importance of energetic factors. In this view aldosterone might increase sodium transport either by increasing the supply of metabolic energy to the sodium "pump," or by facilitating the linkage of metabolism to transport. Recently, it has been suggested that both permeability and energetic factors may be involved [18].

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Isotope Flows and Flux Ratios in Biological Membranes

Cited by 111 publications

References 22 publications

Tracer flux ratios: A phenomenological approach

Tracer flux ratios: A phenomenological approach

Energetics of Sodium Transport in Frog Skin

Effect of aldosterone on active and passive conductance andE Na in the toad bladder

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