Ca
2+ concentrations in perilymph and endolymph of the guinea pig were measured with the double-barreled Ca
2+-selective microelectrodes, and the results showed 1.76±0.74×10
-3M in perilymph and 2.20±0.19×10
-5M in endolymph, respectively. The electrochemical potential gradient for Ca
2+ between perilymph and endolymph was 23.2mV and the active transport mechanism from the former to the latter was thought to exist.
The Ca
2+ concentration in endolymph was abruptly increased in anoxic condition with simultaneous depression of endocochlear potential (EP), and was returned toward preanoxic value after reventilation. Intravenous administration of furosemide (60mg/kg) reduced EP and increased the Ca
2+ concentration in endolymph, but the Ca
2+ concentration did not show a tendency to recover to the initial value in spite of the recovery of EP. Although intravenous injection of furosemide (30mg/kg) or acetazolamide (100mg/kg) caused a slight to moderate depression of EP, the Ca
2+ concentration in endolymph showed little change. These findings suggested that the increase of the Ca
2+ concentration in endolymph in anoxia or furosemide (60mg/kg) administration was attributed to the influx of Ca
2+ from perilymph due to the depression of EP.
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