Module 3: Figure HCN channels
Hyperpolarizing-activated cyclic nucleotide-gated (HCN) channels.
There are four members of the hyperpolarizing-activated cyclic nucleotide-gated (HCN) channel family. Each subunit has six transmembrane (TM) domains, with a pore-forming loop located between TM5 and TM6. The voltage sensor is located in TM4, which has a large number of positive charges that sense the change in voltage to bring about the conformational change that opens the channel pore. The C-terminal region that faces the cytoplasm has the cyclic nucleotide-binding domain (CNBD) that responds to cyclic AMP.