Calmodulin regulation of cyclic-nucleotide-gated channels

Cyclic-nucleotide-gated (CNG) channels play key roles in photoreceptor and olfactory signal-transduction pathways. Recent studies have focused on the molecular characterization of CNG channel subunits and on the identification of the structural domains that contribute to ligand selectivity and affinity, ion gating and permeation, and regulation of channel activity. Calmodulin has been shown to bind directly to the rod and olfactory channels and to modulate their sensitivity to cyclic nucleotides. This Ca2+-dependent regulation of channel activity appears to play a role in the termination of the signal-transduction pathway in olfactory neurons and rod photoreceptor cells. It remains to be determined whether calmodulin also regulates the activity of related channels in other cells.