Calcium signalling and regulation in olfactory neurons

The odorant-induced Ca2+ increase inside the cilia of vertebrate olfactory sensory neurons controls both excitation and adaptation. The increase in the internal concentration of Ca2+ in the cilia has recently been visualized directly and has been attributed to Ca2+ entry through cAMP-gated channels. These recent results have made it possible to further characterize Ca2+'s activities in olfactory neurons. Ca2+ exerts its excitatory role by directly activating Cl− channels. Given the unusually high concentration of ciliary Cl−, Ca2+'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, Ca2+ mediates odorant adaptation by desensitizing cAMP-gated channels. The restoration of the Ca2+ concentration to basal levels occurs via a Na+/Ca2+ exchanger, which extrudes Ca2+ from the olfactory cilia.