Curr. Topics Membr. 53, 119-134.

The calcium-activated chloride conductance in olfactory receptor neurons.

Kleene, SJ

Department of Cell Biology, Neurobiology, and Anatomy, University of Cincinnati, Cincinnati, Ohio 45267-0667

In vertebrates, a Ca²⁺-activated Cl¯ channel plays a central role in the transduction of odorous stimuli.   Odorous stimulation causes a depolarizing influx of Ca²⁺ into the dendritic cilia of the olfactory receptor neurons.   If sufficient Ca²⁺ enters, it activates Cl¯ channels in the ciliary membrane.   As a result, Cl¯ leaves the cilium, causing a further depolarization.   The Cl¯ channels have been identified in olfactory receptor neurons in rat and in several amphibians.   Single channels have not been observed, but noise analysis suggests that they have a unitary conductance of 0.8 pS.   They are activated by cytoplasmic Ca²⁺, which is half-maximally effective at 5-20 μM.   The channels are permeable to anions as large as gluconate^-, implying a pore size of at least 5.8 Å.   Nine inhibitors of the channel have been identified, but many of these have effects on other channels as well.   During transduction, as much as 85% of the total receptor current passes through the Cl¯ channels.   Because of the small size of the channels, this amplification is achieved with very little increase in noise.   Nothing is known about the structure of the channel or of its distribution beyond the dendrites of olfactory receptor neurons.