IS IT A BARRIER?

TEER: resistance across the layer

Transendothelial electrical resistance, or TEER, passes a small alternating current across the cell layer. Tighter junctions make it harder for ions to cross, so the resistance goes up.

TEER is fast, repeatable, and does not harm the cells.

THE FORMULA

From ohms to ohm square centimeters

TEER = (R_cells − R_blank) × A

R_cells is the reading with cells, R_blank is an empty insert with the same medium, and A is the membrane area in cm². Example: a 300 Ω reading with a 100 Ω blank on a 1.12 cm² insert gives (300 − 100) × 1.12 ≈ 224 Ω·cm².

Multiplying by area makes results comparable across insert sizes.

WHAT'S GOOD

Typical TEER values

In the body Rodent brain vessels have been measured at about 1,500 Ω·cm² or more

Immortalized lines Common lines such as hCMEC/D3 usually stay below about 50 Ω·cm²

Stem-cell derived Some protocols report hundreds to a few thousand Ω·cm², and results vary widely between labs

Higher is better, but the exact number depends on the method and the lab.

PERMEABILITY

Do molecules leak through?

P_app = (dQ/dt) ÷ (A × C₀)

Add a tracer such as sodium fluorescein, Lucifer yellow, or a fluorescent dextran to the top compartment, and sample the bottom over time. Q is the amount that crosses, A is the membrane area, and C₀ is the starting concentration on top. The result is in cm/s, and a tight barrier gives a low number.

Papp is a direct measure of how easily a molecule gets across.

USE BOTH

Two views of the same barrier

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TEER

Fast and repeatable, and it senses ion leak through the seal

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Permeability

Direct, since it measures the actual molecules of interest crossing

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Together

A good model has high TEER and low tracer leak

Reliable models are checked from more than one angle.

UNIT 8 STUDY COMPLETE

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Ready for the Fab Challenge?

You've learned how electrical resistance and tracer leakage show whether a barrier is tight.