Fig. 1. The model of drug uptake from supernatant (CS) into human lung microvascular endothelial cells by diffusion (CD) and by facilitated transport (CT). The drug can enter the cells by passive diffusion, characterized by a partition coefficient (H), or by facilitated transport, characterized by a rate constant for association with a specific cellular or subcellular binding site (kt). Intracellular transfer between CTand CDis assumed to move only in the direction characterized by the transfer rate constant (ko).