Among the cells of the inner ear, the outer hair cells (OHCs) are the most important targets of noise-induced effects, being the most sensitive cell types. The aim of this study was to examine the effects of noise (50 Hz-20 kHz, 80 dB sound pressure level, 14 days) on intracellular calcium levels and on the expression pattern of purinoceptors in the membrane of the OHCs of the guinea pig and to measure the stiffness changes of the lateral membrane of these cells. In noise-exposed animals, the resting intracellular calcium concentration increased compared to nontreated animals and was slightly higher in the cells of the basal (219 ± 29 nM) than in the apical (181 ± 24 nM) turns of the cochlea. After application of 180 μM adenosine triphosphate, the intracellular calcium level rose by 60 ± 22 nM in cells from the apical and by 44 ± 10 nM in cells from the basal turns, significantly less than in nontreated animals. Expression of the P2X1, P2X2, P2X4, P2X7, P2Y1 and P2Y4 receptor subtypes was suppressed, while expression of the P2Y2 subtype did not decrease in either of the two preparations. In parallel with the increase in intracellular calcium concentration, the stiffness of the lateral wall of the OHCs was increased. Noise-induced changes in intracellular calcium homeostasis and subsequently in the calcium-dependent regulatory mechanisms may modify OHC lateral wall stiffness and may lead to reduction of the efficacy of the cochlear amplifier.
The Journal of Membrane Biology – Springer Journals
Published: Apr 28, 2007
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