Calcium signalling in hair cells: multiple roles in a compact cell.

Ca2+ is critical for mechanosensory adaptation, frequency tuning, afferent synaptic transmission, and efferent modulation in hair cells. These four processes involve cytoplasmic Ca2+ in three independent signalling pathways. Recent work suggests that Ca2+ regulates a myosin adaptation motor, and that a mobile Ca2+ buffer is highly concentrated in hair cells. Focal Ca2+ entry and the cytoplasmic Ca2+ buffer help to separate these pathways by limiting the spread of Ca2+ signals.