EFFECTS OF FREE-RADICALS ON THE INTRACELLULAR CALCIUM-CONCENTRATION IN THE ISOLATED OUTER HAIR CELL OF THE GUINEA-PIG COCHLEA

The cytosolic free calcium concentration ([Ca2+]i) isolated from the cochlear outer hair cell (OHC) of the guinea pig was measured using microfluorimetric imaging technique and the effects of free radicals were investigated. Hypoxanthine (HX) plus xanthine oxidase (XO) induced a rise in [Ca2+]i in the presence of external Ca2+. Elimination of external Ca2+ (pCa = 7) did not show an increase in [Ca2+]i, indicating that the increased [Ca2+]i is dependent on external Ca2+. The elevation of [Ca2+]i induced by HX-XO was reduced by addition of superoxide dismutase or nifedipine but not by addition of catalase. A single admission of HX or XO failed to affect [Ca2+]i. These findings suggest that superoxide anion generated in the OHC increases the Ca2+ influx across the membrane, presumably leading to some pathological changes in the acoustic transduction by modulating the OHC motility.