3.7 : 细胞膜与药物运输

Drugs encounter multiple barriers to reach their target site within the body, including the multiple-cell layered skin, single-layered intestinal epithelium, and the plasma membrane.

The plasma membrane forms the cellular boundary, protecting the cell's integrity while enabling selective substance exchange. It comprises phospholipids, carbohydrates, and proteins, forming a highly ordered structure.

Phospholipids form a bilayer with their hydrophilic heads facing outwards and hydrophobic tails facing inwards. These bilayers are interspersed with transmembrane proteins such as receptors, ion channels, structural anchors, or transporters, transducing several cellular activities.

Drug passage across these cellular barriers primarily occurs through passive or active transport mechanisms.

Most drugs undergo passive diffusion, moving along their concentration gradient and crossing the cell membrane with or without a transporter. Some employ the paracellular pathway, traversing the gap between adjacent cells.

In contrast, active transport involves drugs moving against their concentration gradient via transporters powered by ATP.