Odor recognition and second messenger signaling in olfactory receptor neurons.

The detection of volatile odorants is supposed to begin with their interaction with soluble binding proteins which shuttle the hydrophobic ligands through the aqueous mucus layer towards specific odorant receptors in the ciliary membrane of olfactory neurons. A large family of receptors for odorants has been identified recently; individual receptor types are expressed in subsets of cells distributed in distinct zones of the olfactory epithelium. Ligand-receptor interaction triggers a rapid multistep reaction cascade, ultimately leading to an electrical response of the receptor neuron. Olfactory signaling is terminated by phosphorylation of receptors via a negative feedback reaction catalyzed by two types of kinases.