Flux Ratios and Isotope Interaction in an Ion Exchange Membrane

Self Cite

In a composite membrane with heterogeneous channels, prevention of net volume flow with hydrostatic pressure differences and/or impermeant osmotic solutes may induce positive isotope interaction (coupling of isotope flows) consequent to circulation of volume flow. The permeability coefficient for net flow will then exceen the tracer permeability coefficient. A permeant osmotic solute will induce either positive or negative isotope interaction, according to whether membrane heterogeneity is more marked for the test solute or the osmotic solute, respectively. Thus membrane heterogeneity may account for phenomena commonly attributed to "single file diffusion". For sufficiently small flows the general flux ratio relationship for homogeneous membranes will continue to apply.

Section: Absence Of Hydrostatic Pressure Difference (Ap =0)supporting

confidence: 60%

Section: Jvcmentioning

confidence: 70%

Influence of membrane heterogeneity on kinetics of nonelectrolyte tracer flows

Essig

1976

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“…The deviation from unity in the ratio RX/R (= P/P*) in the experiments of these authors [3,6] is clearly caused by interactions between the solute particles of a single species ("isotope interaction"), while the deviation seen in toad bladder may not be attributable to this phenomenon because it varies with the nature of the anion accompanying sodium [-1]. An adequate explanation for this interesting property of biological membranes is as yet lacking.…”

Section: Discussionmentioning

confidence: 99%

“…However, substantial differences between tracer and bulk diffusion coefficients for various solutes have been observed in both artificial [3] and biological [1] membranes. Such differences can be produced by (1) coupling between the flows of tracer and abundant species, (2) unstirred layers, (3) coupling between the flow of the test species and other solutes or the solvent, (4) the presence of fixed or mobile carriers within the membrane, (5) electroosmosis, (6) concentration polarization, or (7) other unknown mechanisms.…”

mentioning

confidence: 99%

Effect of transepithelial concentration gradients on the passive fluxes of sodium across toad bladder

Chen

Walser

1976

Bidirectional sodium fluxes across toad bladder were measured after eliminating active transport with ouabain. Mucosal sodium concentration, Cm, was progressively reduced (from 114 to 3 mM) 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 coefficient, P, was found to remain constant as Cm decreased. Equations were derived on this basis for bidirectional fluxes and for P and P as functions of Cm, which corresponded closely to the observed data. The explanation for the observed value of Q and its constancy under these conditions is uncertain.

“…It is well known that several considerations prevent the use of the flux ratio for the precise evaluation of energetic parameters [4,6,10,12,17,20,24,25]. It is perhaps not .generally appreciated however that, even when leakage is minimal and unaffected by experimental procedures, passive tracer flux may make the flux ratio grossly misleading.…”

Section: The Flux Ratio; Influence Of Leakagementioning

confidence: 96%

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

Saito

Essig

1973

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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].