ELECTRON-PROBE MICROANALYSIS OF GENTAMICIN-INDUCED CHANGES ON IONIC COMPOSITION OF THE VESTIBULAR GELATINOUS MEMBRANE

Gentamicin-induced changes in ionic composition in the otolithic membr ane of adult OF1 mice were evaluated in the gelatinous layers of the s accule and utricle by quantitative electron probe X-ray microanalysis. The otolithic membranes were plunge-frozen and freeze-dried to preven t the redistribution of elements. Quantitative analysis was carried ou t with an energy dispersive detector using the peak-to-background (P/B ) ratio method and different salts dissolved in dextran as standards t o calibrate the P/B ratio against the concentration of the elements P, S and K in the microprobe. Gentamicin selectively decreased the conce ntrations of P (P < 0.001) and S (P < 0.01) in the gelatinous membrane of the saccule, and had no effect in the utricle. The concentration o f K also increased in the utricular gelatinous membrane (P < 0.05). Th e mechanism of ototoxicity in the gelatinous membrane is unknown, but the ability of aminoglycosides to block calcium channels may induce di sturbances in the ionic equilibrium of the endolymphatic fluid, and th us affect the biochemical composition of the gelatinous membrane. This technique can be useful to evaluate the distribution of ions in the p rocess of drug-induced ototoxicity.