Fig. 1.

Schematic representation of the intracellular components of olfactory signal transduction pathways. Here, a 7 transmembrane odorant receptor protein (OR) lying within the ORN dendrite interacts directly with odorants or alternatively (?) in the context of odorant-binding protein (OBP) complexes. In both cases, subsequent interactions with heterotrimeric G-protein complexes (G/G′) activate downstream effector enzymes adenyl cyclase (AC) and phospholipase C (PLC). This leads to the synthesis of the second messengers cyclic AMP (cAMP), diacylglycerol (DAG) and inositol 1,4,5 triphosphate (IP₃) that regulate several cation (Na⁺, Ca⁺⁺) channels that carry the transduction current. In addition, OBPS are hypothesized (?) to interact with odorant degrading enzymes (ODEs) to clear unbound ligand from the extracellular space. Signaling is terminated (bulbed lines) by decoupling of OR/G-protein complexes by arrestins (A) and G-protein coupled receptor kinases (GRKs).