Opening Mechanotransducer Channels

Rapid sensory transduction in hair cells is made possible by the direct coupling of stereocilia displacement to ion channels. This week, Ricci et al. examined the extraordinarily fast (and thus difficult to measure) kinetics of these mechanotransducer (MET) channels, and how kinetics shapes transduction. MET channels open rapidly in response to deflections of the hair bundle and then adapt (close) in a calcium-dependent manner. The authors took advantage of slower adaptation in turtle hair cells tuned to low frequencies to measure activation kinetics. The channels opened in two phases: a fast invariant process and a slower process determined by the stimulus amplitude. The dependence on stimulus amplitude supports the view that channel gating is triggered by mechanical displacement. Highfrequency cells, measured in low calcium to reduce adaptation, activated approximately twofold faster. The authors conclude that channel activation and adaptation kinetics impose a bandpass filter on transduction.