Calcium signalling and regulation in olfactory neurons.
The odorant-induced Ca(2+) increase inside the cilia of vertebrate olfactory sensory neurons controls both excitation and adaptation. The increase in the internal concentration of Ca(2+) in the cilia has recently been visualized directly and has been attributed to Ca(2+) entry through cAMP-gated channels. These recent results have made it possible to further characterize Ca(2+)'s activities in olfactory neurons. Ca(2+) exerts its excitatory role by directly activating Cl(-) channels. Given the unusually high concentration of ciliary Cl(-), Ca(2+)'s activation of Cl(-) channels causes an efflux of Cl(-) from the cilia, contributing high-gain and low-noise amplification to the olfactory neuron depolarization. Moreover, in combination with calmodulin, Ca(2+) mediates odorant adaptation by desensitizing cAMP-gated channels. The restoration of the Ca(2+) concentration to basal levels occurs via a Na(+)/Ca(2+) exchanger, which extrudes Ca(2+) from the olfactory cilia.
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Istituto di Cibernetica e Biofisica, Consiglio Nazionale delle Ricerche, Via De Marini 6, 16149, Genova, Italy. menini@icb.ge.cnr.it
D002118:Calcium / Q000502:physiology*; D018118:Chloride Channels / Q000502:physiology*; D000242:Cyclic AMP / Q000502:physiology*; D006801:Humans; D018034:Olfactory Receptor Neurons / Q000502:physiology*; D018035:Receptors, Odorant / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology*
D018118:Chloride Channels; D018035:Receptors, Odorant; D000242:Cyclic AMP; D002118:Calcium