Cholinergic Inhibition of Hair Cells

In the inner ear, the activity of hair cells that transform sound into electrical signals is modulated by a descending efferent innervation from the brain. A major component of this feedback involves cholinergic inhibition of hair cells via an unusual ionic mechanism. It activates rapidly (on the order of milliseconds), but instead of being mediated by a hyperpolarizing conductance through γ-aminobutyric acid (GABA) and/or glycine receptors, it is served by nicotinic cholinergic receptors (nAChR), which usually mediate excitatory postsynaptic responses. How is fast inhibition accomplished if the activation of a cationic channel (the nAChR) at the resting membrane potential should depolarize the hair cell?