Characterization of the calcium influx induced by depolarization of guinea pig cochlear spiral ganglion cells.

We examined dynamic changes in intracellular calcium ion concentrations ([Ca2+]i) in isolated cochlear spiral ganglion cells (SGCs) of the guinea pig using digital imaging microscopy and the Ca(2+)-sensitive fluorescence dye fura-2. [Ca2+]i in SGCs was 83 +/- 22 nM (n = 50, means +/- SD) in cell somata at the resting state. Reversible increases in [Ca2+]i were elicited during membrane depolarization by high K+ (150 mM). This increase in [Ca2+]i was not observed under conditions of depolarization in Ca(2+)-free medium containing 1 mM EGTA. In addition, these increases in [Ca2+]i were sensitive to L-type calcium channel ligands, viz., antagonized by nifedipine (50 microM), verapamil (10 microM) and enhanced by BAY K 8644 (1 microM). These observations suggest that increases in [Ca2+]i of cochlear SGCs induced by high K+ are due to an influx of extracellular Ca2+, probably through voltage-gated L-type calcium channels.