Activation of olfactory cyclic‐nucleotide gated channels revisited

Abstract

Ion channels that are gated by cyclic nucleotides (CNG channels) have been best studied for their roles in visual and olfactory sensory transduction. Sensory stimulation of vertebrate photoreceptors by light and olfactory receptor neurones (ORNs) by odorants activates 7-transmembrane receptors, and triggers, via a G protein, changes in the intracellular concentration of second messenger cyclic nucleotides. In the case of photoreceptors, the G protein Gt stimulates phosphodiesterase leading to the hydrolysis of cGMP, which in turn promotes closure of cGMP-gated channels and hyperpolarization. In the case of ORNs, the G protein Golf stimulates adenylyl cyclase to produce cAMP, which promotes opening of cAMP-gated channels and depolarization. The ability of CNG channels to be gated by cyclic nucleotides is therefore crucial for organisms to monitor their visual and odorant environments.