Figure 1.

Structure of a generic tetrameric cation channel. The pore domain (in blue) is found in all tetrameric cation channels. This region of the channel selectively transports ions across the membrane and integrates regulatory signals through transmembrane and intracellular regulatory domains that can be attached to the N or C terminus of the channel (in gray). In the K⁺ channel pore shown here, the selectivity filter (in yellow) is composed of discrete ion-binding sites indicated with the green spheres. Other tetrameric cation channels (Na⁺, Ca²⁺, and nonselective) have the same overall architecture but with a different selectivity filter.