TIGHT JUNCTION

TER vs Flux
TIGHT JUNCTION
TJ Proteins
TJ Function
TJ Environment
TJ Regulation
TJ Channel
TER vs Flux
TJ Maintenance
Occludin
ZONAPSE
Both MDCK II and HT29 cells have low TER.  MDCK II cells have intact tight junctions as assessed by EM and localization of occludin.  However, HT29 cells do not form tight junctions and lack occludin expression.  Mannitol flux assays faithfully report that MDCK II cells exclude flux whereas HT29 cells allow free diffusion of the tracer across the paracellular pathway.

Epithelial Cells
TER
Mannitol Flux
C2bbE1 (clone of Caco-2)
Medium
Low
HT29
Low
High
T84
High
Low
MDCK I
High
Low
MDCK II
Low
Low

Problem with TER:

First Senario: Two cell types (Cell#1 and Cell#2) have the SAME sodium and chloride permeabilities but have DIFFERENT electrical conductane. Explanation: Paracellular channel of Cell#1 has higher calcium binding affinity. Binding of calcium to the channel blocks the flow of sodium and chloride, causing a decrease in ionic conductance of the cell monolayer.

Second Senario: Two cell types (Cell#3 and Cell#4) have DIFFERENT sodium and chloride permeabilities but have the SAME electrical conductane. Explanation (A): Paracellular channel of Cell#3 can have permeability ratio of sodium to chloride as 10 to 1 while Cell#4 can have peremability ratio of sodium to chloride as 1 to 10. Explanation (B): Paracellular channel of Cell#3 can have permeability ratio of sodium to calcium as 1 to 1 while Cell#4 can have peremability ratio of sodium to chloride as 1 to 60, if conductance is measured in a solution containing sodium to calcium at 60 to 1.

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