Directed transport in renal proximal tubule cells

A method is proposed to quantify the directed transport flux resulting from a monolayer of polarized proximal tubule cells seeded onto a microporous membrane. The experimental system is comprised of two well mixed fluidic chambers sandwiching the membrane-cell construct. A mathematical model is developed to describe active and passive transport independently across the cell monolayer. The model is comprised of three coupled ordinary differential equations describing the transported solute concentrations in the two chambers and the cell layer. The main parameters in the model are the membrane permeability, cell layer permeability and transporter constants. An analytical solution is derived for the linear equations arising from the assumption of first order transporter activity. The method is more direct as it does not require application of inhibitors of transporter activity, and thereby reduces the number of experiments and simplifies data interpretation. Some limiting features are also discussed.