GENTAMICIN OTOTOXICITY IN OTOCONIA - QUANTITATIVE ELECTRON-PROBE X-RAY-MICROANALYSIS

Chronic gentamicin ototoxicity was evaluated in the otolithic membrane of adult OF1 mice at the otoconial layer of the saccule and utricle b y quantitative electron probe X-ray microanalysis of Ca and K. The oto lithic membranes were plunge-frozen and freeze-dried. The analysis was carried out with an energy dispersive detector using the peak-to-back ground ratio method and different inorganic salts of Ca and K as stand ards to calibrate the microprobe. Ca and K in the otoconia are related via a linear function in both the saccule and the utricle. This assoc iation is not maintained after exposure to gentamicin, which suggests that this aminoglycoside antibiotic interferes with the Ca - K equilib rium in the otoconia. A dose of 200 mg/kg gentamicin twice a day for 5 days did not affect Ca in the mineral phase of the otoconia, but did increase K in both saccular (p < 0.05) and utricular (p < 0.01) otocon ia. These increases in K may reflect a modification in the composition of the endolymph, resulting from cellular damage at the plasma membra ne.