You could try Trans Epithelial Electric Resistance (TEER) Measurements.

http://www.pharmaceutical-int.com/article/trans-epithelial-electric-resistance-teer-measurements.html

This group did a lot of this work:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3771947/

Thanks for the information Ross,

Barrier integrity is easily assessed by using HRP-dextran, polycarbonate filters (8.0 micrometer pore size), and plate reader.  Add HRP-dextran to the upper layer of confulent monolayers on polycarbonate filter. After 60 minutes incubation, collect the medium of lower compartment, develop a color, and measure the absorbance by plate reader. If you want to know the details, please refer the manuscript "Alcohol Clin and Exp Res 2005  29(12) 2116-2122". This experiment is a simple method, need not expensive laboratory instruments, and can determine directly the cell permeability. Please try this methods.

Thanks Hiroshi, I will definitively try the method,

Does the HRP-dextran method  work using smaller polycarbonate filters (i.e. 0.5 micrometer pore size)? Thanks!

Regrettablly, we did not do experiments using combination of both 0.5 micrometer pore size polycarbonate filetes and 40kDal HRP dextran. However, diameter of 40kDal protein is 2nm (similar size with endotoxin), and pore size of filter is 500 nm(=0.5micrometer), larger than that of 40kDal HRP. Therefore, theoretically, 40kDal HRP-dextran work using smaller filters. Good luck!!

Thank you very much for your answer. As you suggest, it should work as well. I will give it a try!