Measurement of [Ca2+]i and [Na+]i in outer hair cells isolated from gerbil cochlea

Outer hair cells (OHCs) become sodium- and calcium-overloaded after being isolated in high-sodium medium. Most of the sodium and calcium leak occurs through 10-15% of the transduction channels that are open at the resting position of the hair bundle. However, [Ca2+]i and [Na+]i in OHCs can vary greatly from cell to cell even though they all appear normal. Different [Ca2+]i and [Na+]i may result from different leak conductance through the transduction channels. The leak was determined by the degree of damage inflicted upon the tip-link of the hair bundle during isolation. Excessive sodium accumulation may explain why OHCs cannot maintain their normal resting membrane potential in some experimental conditions.