A laminar flow absorption model for a carrier-mediated transport in the intestinal tract.

A laminar flow absorption model for a carrier-mediated transport was developed to analyze the data of the intestinal single perfusion experiment. By using this model, we calculated the absorption rate and the concentration of the substance (drug) at the aqueous-intestinal membrane interface (cwall). The absorption rate was smaller than that predicted by the Michaelis Menten equation, using the concentration at the inlet (c0). The apparent Michaelis constant (Km,app) was larger than the true Michaelis constant (Km), if the data were analyzed by using the simulation curve of the absorption rate vs. c0 as the usual method. This is because cwall was smaller than c0. But the maximal transport velocity (Vmax) was little affected, because cwall became almost equal to c0 when c0 was high. By using this model, we can determine the values of Vmax and Km which are not biased by the unstirred water layer in the intestinal tract.