Ion channels are pore-forming proteins that cross the lipid membrane of cells and selectively conduct ions across this hermetic wall. Ion channels are responsible for the generation of electrical signals in most tissues and thus are involved in every heart beat, every perception, every thought, etc. Opening of ion channels allows ions to move along their electrochemical gradient thus either depolarizing the membrane or repolarizing it and creating electrical patterns such as the action potential (see Chapter 9 and Figure 11-1).