Mechanism of lack of development of negative endocochlear potential in guinea pigs with hair cell loss

The endocochlear potential (EP), and the concentration of K⁺, Na⁺ and Cl^- were measured simultaneously in endolymph of guinea pigs. The EP was 85.6±0.8 mV in normal guinea pigs, 90.7±0.8 mV in the kanamycin-treated animals, and 91.6 ±1.2 mV in those treated with nitrogen mustard-N-oxide (NMNO). Thirty minutes after the onset of anoxia, the EP (negative EP) was -29.3 ± 1.0 mV in the normal group, -0.2±1.0 mV in the kanamycintreated group, and -1.9±1.3 mV in the NMNO-treated group. The permeability coefficients of K⁺ (P_k), Na⁺ (P_na) and Cl^- (P_cl) across the endolymph-perilymph barrier during the period of 20-30 min after the onset of anoxia in the normal group were (341.6±38.2) × 10^-9 cm³ sec^-1, (53.0±8.1) × 10^-9 cm³ sec^-1 and (111.8±27.2) × 10^-9 cm³ sec^-1, respectively. P_k was decreased in the kanamycin- and NMNO-treated groups. P_na did not differ between the normal and treated groups. P_cl was increased in the kanamycin- and NMNO-treated groups. The K⁺:Na⁺:Cl^- permeability ratio was 1:0.16:0.32 in the normal group, 1:1.12:11.6 in the kanamycin-treated group, and 1:0.44:5.60 in the NMNO-treated group. The results indicate that the lack of development of a negative EP in the kanamycin- and NMNO-treated guinea pigs was attributable to the increased P_cland the decreased P_k across the endolymph-perilymph barrier, probably the organ of Corti. during anoxia.