A. Fridberger et al., ACOUSTIC OVERSTIMULATION INCREASES OUTER HAIR CELL CA2+ CONCENTRATIONS AND CAUSES DYNAMIC CONTRACTIONS OF THE HEARING ORGAN, Proceedings of the National Academy of Sciences of the United Statesof America, 95(12), 1998, pp. 7127-7132
The dynamic responses of the hearing organ to acoustic overstimulation
mere investigated using the guinea pig isolated temporal bone prepara
tion. The organ was loaded with the fluorescent Ca2+ indicator Fluo-3,
and the cochlear electric responses to low-level tones were recorded
through a microelectrode in the scala media. After overstimulation, th
e amplitude of the cochlear potentials decreased significantly. In som
e cases, rapid recovery was seen with the potentials returning to thei
r initial amplitude. In 12 of 14 cases in which overstimulation gave a
decrease in the cochlear responses, significant elevations of the cyt
oplasmic [Ca2+] in the outer hair cells were seen. [Ca2+] increases ap
peared immediately after terminating the overstimulation, with partial
recovery taking place in the ensuing 30 min in some preparations. Suc
h [Ca2+] changes were not seen in preparations that were stimulated at
levels that did not cause an amplitude change in the cochlear potenti
als. The overstimulation also gave rise to a contraction, evident as a
decrease of the width of the organ of Corti. The average contraction
in 10 preparations was 9 mu m (SE 2 mu m). Partial or complete recover
y was seen within 30-45 min after the overstimulation. The [Ca2+] chan
ges and the contraction are likely to produce major functional alterat
ions and consequently are suggested to be a factor contributing strong
ly to the loss of function seen after exposure to loud sounds.