Eps8 regulates K+ current expression in mouse cochlear inner but not outer hair cells nor in vestibular type I and type II hair cells

Eps8 is involved in modulating cell signaling and receptor trafficking, via its range of protein interactions. We recently showed that cochlear inner and outer hair cells of Eps8 knockout (KO) mice, which are born deaf, show shorter stereocilia than wild type (WT) mice [1]. Inner, but not outer, hair cells, moreover, showed an altered expression of the mature array of voltage-dependent K+ channels, despite the fact that they express similar conductances. Vestibular hair cells of Eps8 KO mice show shorter stereocilia than normal [2], too. However, it is not known if this is accompanied by some functional defect. We therefore patch-clamp whole-cell recorded the voltage-dependent K+ currents from vestibular Type I and Type II hair cells of Eps8 KO and WT mice at different postnatal developmental stages. We found that both vestibular hair cell types from KO mice showed a normal pattern of expression of K+ currents along with maturation up to the adult age. These results indicate that Eps8 is a specific regulator of K+ channel expression in mammalian cochlear inner hair cells. This notion appears particularly important in view of the recent discovery that a nonsense mutation in EPS8 is responsible for a non-syndromic form of human deafness [3].