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Measurement of barrier function of cell layers in tissue
culture via ECIS has proven to be a significant and rapidly growing use of
this technology. The utilization of ECIS to monitor barrier function was
first demonstrated in 1992 using bovine pulmonary endothelial cells exposed
to thrombin.
In the decade following that publication, endothelial cell
biologist have increasingly found barrier function measurements via ECIS to
be an attractive alternative to techniques involving the use of membrane
inserts and Using chambers. In addition to its convenience in gathering
transcellular resistance (TER) data with a minimum of labour, the
measurement requires no tagged compounds and associated sampling/measuring
techniques. The relatively low values of the transcellular resistance for
most endothelial layers (for example 10 ohm cm2) make precise
determinations of this value difficult with other technologies such as
resistance measurements of cell layers upon filter substrates. |
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True barrier function measurements |
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Cell layers with very high TER values such as
endothelial cells from the brain and epithelial cells exhibiting tight
junctions can be measured electrically using porated membrane supports as
well as with ECIS, but there is an important distinction between the
capabilities of these methods. In both cases, the true barrier function (the
resistance of the paracellular pathway between the cells) is complicated by
the constricted current flow in the space between the basal cell membrane
and the cell support. This complication is equally true for measurements
using tagged compound. This is shown in the figure below where we see a
cartoon version of cells upon a porated filter. Note that for molecules to
travel from the lower chamber to the space above the cell layer, they must
also travel in the constricted space beneath the cells to reach the
intercellular junctions. Because of this, one does not measure the true
barrier function but rather a combination of the constricted paths beneath
the cells and the transcellular pathway. |
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The ECIS method is unique in being able to
distinguish between these two pathways, since they each affect the measured
resistance and capacitance monitored by ECIS in different ways. Using a
published model , the true barrier function due to intercellular junctions
can be extracted from ECIS data.
Garcia, et al., have used this model to address the changes in impedance
when bovine pulmonary arterial endothelial cell layers are exposed to VEGF.
Data analyzed by the model show a drop in the true barrier function in
response to the growth factor.
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Lo, C.M., Keese, C.R., Giaever, I., "Cell-substrate
contact: Another factor may influence transepithelial electrical resistance
of cell layers cultured on permeable filters", Experimental Cell Research,
250 (2): 576-580 (1999)] |
| For more details regarding true barrier
function measurements and the complication associated with porated filters. |
