CHARACTERIZATION OF THE CALCIUM INFLUX INDUCED BY DEPOLARIZATION OF GUINEA-PIG COCHLEAR SPIRAL GANGLION-CELLS

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