Low concentration of FBS inhibiting trypsin? - (Dec/09/2009 )

As per the question.

I tried lifting some cells (MSCs) and about 2 thirds of them came off nicely, but the rest just stuck there and wouldn't come away, even after giving the flask a good tap.

I removed the lifted cells with all the trypsin and added a bit more fresh trypsin to the flask - the remaing cells then lifted straight away.

This suggests that the 1st dose of trypsin had lost its activity.

The flask had been washed with saline after removal of the medium, so most of the FBS would have gone, though there would be a trace left by definition.

Is there anything known about trypsin inhibition by small traces of FBS?

Cheers
Chris

For what it's worth, I never wash my cells in PBS/saline before trypsin, they always come off.