Membrane properties of chick semicircular canal hair cells in situ during embryonic development

The electrophysiological properties of developing vestibular hair cells hav e been investigated in a chick crista slice preparation, from embryonic day 10 (E10) to E21 (when hatching would occur). Patch-clamp whole-cell experi ments showed that different types of ion channels are sequentially expresse d during development. An inward Ca2+ current and a slow outward rectifying K+ current (I-K(V)) are acquired first, at or before E10, followed by a rap id transient K+ current (I-K(A)) at E12, and by a small Ca-dependent K+ cur rent (I-KCa) at E14. Hair cell maturation then proceeds with the expression of hyperpolarization-activated currents: a slow I-h appears first, around E16, followed by the fast inward rectifier I-K1 around E19. From the time o f its first appearance, I-K(A), is preferentially expressed in peripheral ( zone 1) hair cells, whereas inward rectifying currents are preferentially e xpressed in intermediate (zone 2) and central (zone 3) hair cells. Each con ductance conferred distinctive properties on hair cell voltage response. St arting from E15, some hair cells, preferentially located at the intermediat e region, showed the amphora shape typical of type I hair cells. From E17 ( a time when the afferent calyx is completed) these cells expressed I-K, (L) , the signature current of mature type I hair cells. Close to hatching, hai r cell complements and regional organization of ion currents appeared simil ar to those reported for the mature avian crista By the progressive acquisi tion of different types of inward and outward rectifying currents, hair cel l repolarization after both positive-and negative-current injections is gre atly strengthened and speeded up.