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

Abstract

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 cm 3 sec −1, (53.0±8.1) × 10 −9 cm 3 sec −1 and (111.8±27.2) × 10 −9 cm 3 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.