Characterization of Active Transport Parameters

As can be seen, PAM PA measurements can predict fluoroquinolone in vivo data remarkably well, as well as the standard benchmark, Caco-2. Accordingly, they can be complementary tools, quick in approaching the potential of absorption of a potential molecule in the early stages of a discovery project. 

When a saturable transporter is involved in the permeation process, the permeability is no longer a constant value but is dependent on the concentration of the substrate. In that case it is necessary to characterize the parameters of the carrier-mediated process, Km, the Michaelis-Menten constant related with the affinity by the substrate and Vmax, the maximal velocity of transport. If a passive diffusion process occurs simultaneously to the active transport pathway then it is necessary to evaluate the contribution of each transport mechanism. An example of how to characterize the parameters in two experimental systems and how to correlate them are described in the next section. 

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