Putting ion channels to work: Mechanoelectrical transduction, adaptation, and amplification by hair cells

As in other excitable cells, the ion channels of sensory receptors produce electrical signals that constitute the cellular response to stimulation. In photoreceptors, olfactory neurons. and some gustatory receptors, these cha nnels essentially report the results of antecedent events in a cascade of c hemical reactions. The mechanoelectrical transduction channels of hair cell s, by contrast, are coupled directly to the stimulus. As a consequence, the mechanical properties of these channels shape our hearing process from the outset of transduction. Channel gating introduces nonlinearities prominent enough to be measured and even heard. Channels provide a feedback signal t hat controls the transducer's adaptation to large stimuli. Finally, transdu ction channels participate in an amplificatory process that sensitizes and sharpens hearing.