Concentration-dependence of nonelectrolyte permeability of toad bladder

Essig, Alvin; Walser, Mackenzie; Chen, J. S.

doi:10.1007/bf01868829

Cited by 1 publication

(2 citation statements)

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“…If flux is truly paracellular and thus passive, flux values can be easily normalized by dividing the flux by the applied concentration gradient, ∆c, of the marker compound. The resulting value is the paracellular permeability for this compound, usually specified with the unit 10 −6 cm/s (permeability = flux [µmol/h/3.6/cm 2 ] / ∆c [mmol/l = µmol/cm 3 ]) [8,18] and can be used to directly compare values from different studies. If, however, part of the transport is transcellular, as, e.g., demonstrated for fluorescein flux [6] and for 4 kDa FITC-dextran flux [23] in Caco-2 cell layers, then this assumed proportionality between ∆c and flux would no longer hold true, as an active transport component would be saturable.…”

Section: Discussionmentioning

confidence: 99%

“…Permeability of a cell layer for a certain substance is defined as the ratio of the flux of this substance divided by its concentration gradient (∆c) across the cell layer [18]. In the current setting, this implies that the fluorescein flux across a cell layer should depend linearly on the fluorescein concentration within the donor compartment.…”

Section: Linear Dependence Of Fluorescein Flux On the Donor Concentra...mentioning

confidence: 99%

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Integrating Continuous Transepithelial Flux Measurements into an Ussing Chamber Set-Up

Alija,

Knobe,

Pouyiourou

et al. 2024

IJMS

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Fluorescently labelled compounds are often employed to study the paracellular properties of epithelia. For flux measurements, these compounds are added to the donor compartment and samples collected from the acceptor compartment at regular intervals. However, this method fails to detect rapid changes in permeability. For continuous transepithelial flux measurements in an Ussing chamber setting, a device was developed, consisting of a flow-through chamber with an attached LED, optical filter, and photodiode, all encased in a light-impermeable container. The photodiode output was amplified and recorded. Calibration with defined fluorescein concentration (range of 1 nM to 150 nM) resulted in a linear output. As proof of principle, flux measurements were performed on various cell lines. The results confirmed a linear dependence of the flux on the fluorescein concentration in the donor compartment. Flux depended on paracellular barrier function (expression of specific tight junction proteins, and EGTA application to induce barrier loss), whereas activation of transcellular chloride secretion had no effect on fluorescein flux. Manipulation of the lateral space by osmotic changes in the perfusion solution also affected transepithelial fluorescein flux. In summary, this device allows a continuous recording of transepithelial flux of fluorescent compounds in parallel with the electrical parameters recorded by the Ussing chamber.

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