Chapter 16 – Modeling Membrane Transport

This chapter discusses the modeling of the membrane transport. Many substrates cross cell membranes by processes other than passive diffusion. When the transport is carrier-mediated, the carrier modifies the conductance of the membrane and may either increase or decrease the flux of the substrate across the membrane. A common characteristic of all carrier-mediated transport is its saturability, as only a finite amount of carrier is available to for binding the substrate; even the simplest one-site carrier model exhibits saturation. Inclusion of carrier-mediated transport adds additional model parameters that describe the transporter. In addition, the model must account for both labeled (tracer) and unlabeled (mother) substrate. When modeling passage of substrates across membranes, the simplest system is composed of two well-stirred compartments separated by a semipermeable membrane. A model for transport and exchange of tracer between plasma, endothelial cells, interstitial fluid, mucosal cells, and the lumen of the intestine for a single capillary-tissue unit accounts for convection of tracer in the plasma (Fp) and in the lumen of the intestine (Fi). The chapter provides an overview of the single capillary model and complex models.