Developmental changes in the physiology of hair cells.

Mature hair cells express complements of ion channels which vary with hair cell type. Immature hair cells in the inner ears of neonatal mice and pre-hatch chicks share mechanosensitive and certain voltage-gated conductances: delayed rectifier and inwardly rectifying potassium conductances, voltage-gated calcium and sodium conductances. Over the course of several days the immature cells acquire other conductances that confer upon them the distinctive voltage-dependent properties of mature hair cells. In the mouse utricle, postnatal acquisition of additional delayed and inward rectifiers transforms the neonatal hair cells into two classes with the electrophysiological profiles of mature type I and type hair II cells. Electromotility, a highly differentiated, voltage-dependent property of mature outer hair cells from the mammalian cochlea, is also acquired after mechanosensitivity.