The perception of odors begins with depolarization of the olfactory receptor cells. This transduction process is mediated by G
-protein-linked activation of adenylate cyclase, which produces a membrane current by direct gating of cationic channels (cAMP
-gated channels) located in ciliary plasma membrane. Opening of these cAMP
-gated channels allows monovalent as well as divalent cations to enter the ciliary cytoplasm, and this Ca
2+ influx serves two important functions. First, the Ca
2+ influx activates a Cl
- current, which stabilizes the transduction current during fluctuations in extracellular cation concentration and increases the total current activated by cAMP. Second, the Ca
2+ influx mediates adaptation by providing negative feedback at several stages in the transduction mechanism.
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