Permeability coefficient unit, cm/s - (Aug/28/2012 )

Hello all,

I'm working with in vitro BBB model and using 14C-sucrose as a permeability marker. However, I'm not quite getting the concept of permeability coefficient unit, cm/s. I got a permeability coefficient value 2 x 10^-5cm/s. What does this means since cm is a unit for distance and not concentration. Can anyone explain about this?

Thank you

Diffusion rate.