passive membrane transport processes include

Passive membrane transport processes include free#

NTCP is anther symporter and it cotransports bile acid with Na + across the cell membrane fueled by energy created by the Na +-ATPase uniporter. For example, peptide transporter 1 (PEPT1) and peptide transporter 2 (PEPT2) are symporters, cotransporting peptide substrate with H + across the membrane using energy derived from the H +-ATPase uniporter. Typically, the ions will move down the electrochemical gradient through facilitated diffusion coupled with a uniporter, allowing the drug molecule to move against the concentration gradient. They cotransport two or more different molecules or ions across the membrane. Symporters are also termed cotransporters. The secondary active transporters are divided into two types: symporters and antiporters. One is the primary active transporters, which use the energy from hydrolysis of ATP to ADP and P i (e.g., P-gp, BCRP), the other is the secondary active transporters, which typically use energy derived from an electrochemical gradient created by one or more other transporters (e.g., H +-ATPase or Na +-ATPase uniporters). There are two types of active transporters that work against the drug concentration gradient from low concentration to high concentration and require cellular energy.

For example, organic cation transporter 1 (OCT1) is an electrogenic uniporter that can transport organic cations from blood into the cell driven by the negative membrane potential inside the cell.

In facilitated diffusion, transporters (usually uniporters or channels) accelerate the movement of molecules across the membrane through mechanisms like gated pore or rocker switch and it does not require energy. Uptake and efflux transporter mechanisms. Similarly, for paracellular transport, drug molecules go through the tight junctions between the cells driven by drug concentration gradient across the membrane and no energy is required.įigure 9.1.

Passive membrane transport processes include free#

At the steady state, the free drug concentrations on both sides of the membrane are the same.

It is driven by concentration gradient of drugs from high concentration to low concentration and does not require energy from the cell. For transcellular passive diffusion, molecules pass through the bilayer cell membrane into the intracellular space. The roles of passive diffusion, uptake, and efflux transporters are illustrated in Figure 9.1. Many endogenous biochemical compounds that are necessary for life do not have physicochemical properties that allow sufficient passive diffusion, so there are transmembrane transporters that greatly enhance their transport across membranes. A compound must have favorable physicochemical properties (i.e., lipophilicity, hydrogen bonds, molecular weight) to undergo passive diffusion. Passive diffusion is the predominant mechanism for the permeation of drugs throughout the body. Passive sampling devices may come in the form of a badge-like device worn for personal sampling or be mounted for area sampling. These devices are often designed for relatively long-term (up to 3 months) sampling. The time-weighted average concentration is calculated from the mass of analyte in the sampler divided by the volume of air sampled. These samplers commonly contain diffusion barriers that control the sampling rate. Passive diffusion sampling of gaseous compounds involves diffusive transport into the device upon which the analyte either reacts with or is trapped by the sorbent medium, which may be an impregnated filter or molecular sieve. Because they do not require a power supply, they can be used in remote locations. 5,10 Passive diffusion sampling devices, also called Palmes tubes, 1 are generally small, inexpensive, and simple-to-use. Passive diffusion sampling is an alternative to active sampling that does not use pumps, but rather relies on natural diffusion of analytes from the air into the sampling medium. Hageman, in Encyclopedia of Analytical Science (Third Edition), 2019 Passive Sampling