Membrane-bound ion channels play an important role in biological syste
ms. They are involved in key processes such as neural signal transduct
ion, muscle contraction, and vision. The understanding of the structur
e of natural ion channels is growing, but it is still far from satisfa
ctory. Synthetic ion channels can have the advantage of a well-defined
conformation of the active state. This information facilitates the st
udy of the structure-function relationships of their biological counte
rparts.