[Quantitative analysis of the relationship between negative anoxic EP and the number of missing outer hair cells in the guinea pig].
It is thought that the integrity of the hair cell plays an important role in the production of the negative anoxic endcochlea potential EP, because the destruction of hair cells abolished the production of negative anoxic EP. However, the mechanism by which the negative anoxic EP is generated remains controversial although most investigators have regarded negative anoxic EP as diffusion potential across the organ of Corti. We hypothesized that negative anoxic EP was mainly produced by diffusion of ions through the outer hair cells from the scala media to the scala tympani or vice versa. The present study examined the negative anoxic EP and the reduction in the number of hair cells. Kanamycin (300 or 500 mg/kg) or gentamicin (100 or 150 mg/kg) were administered to albino guinea pigs (200 to 300 g) IM for 10 or 15 days in order to induce varying degrees of hair cell loss in the animals. EP was recorded using the round window approach and then hair cells were counted by scanning electron microscopy. The number of missing outer hair cells in the whole cochlea correlated well with the maximum negative EP value, which was defined as the lowest EP value during anoxia. The value of the correlation coefficient was 0.882. The EP value depends on the position at which the EP is recorded. Closer examination indicated that maximum negative EP was well correlated with the number of missing outer hair cells of upper turns, such as the second or third turn, rather than with that of the hook portion, although EP and negative EP was recorded at the hook portion. These results suggested that negative EP reflects the diffusion potential over the entire cochlea. The present results supported our hypothesis that some ions only pass through the outer hair cells in the organ of Corti.
Yasuta
H
H
Department of Otolaryngology, Fukushima Medical College.
Kanno
H
H
D000818:Animals; D015687:Cell Hypoxia; D003051:Cochlea / Q000502:physiology*; D006168:Guinea Pigs; D006198:Hair Cells, Auditory / Q000187:drug effects / Q000473:pathology*; D008564:Membrane Potentials