Inhibition of K+ Currents in Type I Vestibular Hair Cells by Gentamicin and Neomycin

Abstract

Significant ototoxicity limits the use of aminoglycoside (AG) antibiotics. Several mechanisms may contribute to the death of both auditory and vestibular hair cells. In this study the effects of gentamicin and neomycin on K⁺ currents in mature and early postnatal type I vestibular hair cells (HCI) were tested directly. The whole-cell patch clamp technique was used to assess the effects of AG and KCNQ channel modulators on K⁺ currents (I_K) in HCI acutely isolated from gerbil semicircular canals. Extracellular neomycin (1 m<smlcap>M</smlcap>) rapidly reduced peak outward I_K by 16 ± 4% (n = 9) in mature HCI (postnatal days, P, 25-66). Gentamicin (5 m<smlcap>M</smlcap>) reduced outward I_K by 16 ± 3% (n = 8). A similar reduction in outward current was seen in immature HCI (P5-9) that lacked the low-voltage-activated component of I_K observed in mature cells. Intracellular application of gentamicin and neomycin also reduced I_K in mature HCI. Modulators of KCNQ channels were used to probe KCNQ channel involvement. The selective KCNQ antagonist XE991 did not reduce I_K and the neomycin-induced reduction in I_K was not reversed by the KCNQ agonist flupirtine. Application of intracellular poly-<smlcap>D</smlcap>-lysine to sequester PIP₂ did not reduce I_K. Application of the K⁺ channel blocker 4-aminopyridine (4-AP) strongly reduced I_K, and extracellular AG in the presence of 4-AP gave no further inhibition of I_K. In summary, AG significantly reduce the 4-AP-sensitive I_K in early postnatal and mature HCI. K⁺ current inhibition differs from that seen in outer hair cells, since it does not appear to involve PIP₂ sequestration or KCNQ channels.