EFFECTS OF Na⁺, K⁺, AND OUABAIN ON MICROPHONIC POTENTIALS OF THE GOLDFISH INNER EAR

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Microphonic potentials were recorded from the sacculus of goldfish with glass pipette electrodes to study the effects on the potentials of changes in the ionic composition of endo-and perilymph and of administered ouabain. Ions and drugs were applied with perfusion techniques and special attention was paid to the difference in effects between endo-and perilymphatic applications. The results obtained were as follows:
1. No marked changes were found in the amplitude of microphonic potentials when the endolymph was replaced either with 120mm NaCl or with KCl.
2. Microphonic potentials were reduced in size when the perilymphatic K⁺ concentration was raised, and this reduction was reversible when the solution returned to normal. The amplitude of microphonic potentials was linearly related to the logarithm of perilymphatic K⁺ concentrations in a range between 25 and 120mM.
3. A marked reduction in the amplitude of microphonic potentials was produced when over 5×10^-6g/ml of ouabain was applied to the perilymphatic space. An endolymphatic application of ouabain produced no effects even at much higher concentrations. This finding suggests the presence of an active extrusion mechanism of Na⁺ across the membrane at the basal part of hair cells. Functional differentiation between the membrane at the hair-bearing surface and at the basal part of hair cells and the functional significance of a high K⁺ concentration of the endolymph were discussed.