ABSTRACT
Biological cells are enclosed by a phospholipid bilayer, a few nanometres thick, that is almost impermeable to water and water soluble molecules. Ion channels are pro teins embedded in the membrane that control the movement of ions across the membrane. The channel protein, also a few nanometres wide, is arranged in a roughly circular array that spans the membrane with a central aqueous pore that can open 1-58488-362-6/04/$0.00+$ 1.50
The opening and closing of ion channels is called gating. The major types of gating mechanism are voltage gated (where channels respond to changes in the membrane potential) and ligand activated (where channels are activated by binding with molecules of certain chemicals): other types of channel may respond to changes in temperature or stretching by a mechanical force.
