T84 growth in Transwells - (Nov/30/2010 )

Hi all:)
Here's a strange problem I've encountered: has anyone else had this happen?
I'm trying to grow T84 in a monolayer on (Corning) Transwells, and they don't seem to be growing (TER is not increasing, or rather has increased very little during 9 days of culture)on a polycarbonate membrane- however those exact same cells (1 passage older) grow perfectly well and the TER has increased dramatically when grown on a PET membrane! The plates are from the same manufacturer, both 0.4um pore size, both seeded at exactly the same density, using the same media. So basically the only thing that is different is the membrane- and whatever attributes it has.
I have found plenty of papers that have used polycarbonate membranes to grow T84s on, so what is the problem?? Does anyone have any suggestions?
Thanks so much- I'm at a loss...

To follow up my post- we ended up returning those plates to the manufacturer, and getting PET plates, on which cells seem to grow better.