Fig. 3

Electrochemical properties of the mammalian cochlea. a Structure of the cochlea. Overall view of the human ear is illustrated in the upper left panel. The upper right panel shows a cross-section of the cochlea. In the lower panel, the tissue and cellular compositions of the cochlea as well as the electrochemical profiles of endolymph and perilymph (PL) are shown. Note that potassium ions (K⁺) unidirectionally circulate between the two types of lymph (endolymph and perilymph) through the lateral cochlear wall (described as a K⁺ circulation current). The boxed area in a is enlarged in b. b Structure and molecular architecture of the lateral wall. The scheme shows that this tissue is made up of outer and inner layers; between the two layers lies the intrastrial space (IS). Ion channels and transporters, which are likely to play a crucial role in the maintenance of endolymphatic high potential and of the K⁺ circulation current, are also described. ClC ClC-K/barttin-type chloride ion (Cl⁻) channel, Kir4.1, KCNQ1/KCNE1 K⁺ channels, NKCC Na⁺, K⁺, 2Cl⁻-cotransporter, NSC nonselective cation channel. v_OB, v_OA, v_IB, v_IA Membrane potential on the basolateral (subscript B) and apical (subscript A) surfaces of the outer (subscript O) and inner layer (subscript I). c Potential and ion profiles of the lateral wall, perilymph, and endolymph. Red lines and numbers and blue bars indicate the potential relative to perilymph and K⁺ concentration [K⁺] , respectively. In each of the five panels (a–e), representative in vivo measurements obtained under the different conditions described above the blue bars are shown. Ouabain and bumetanide are inhibitors of sodium ion (Na⁺), K⁺-ATPases and NKCC, respectively. The upward and downward arrows show the increase and decrease of [K⁺], respectively. iv Intravenous injection. Images in a–c were reproduced and adapted from Nin et al. [24]