GLUTAMATE-INDUCED INTRACELLULAR CA2-CELLS OF THE GUINEA-PIG COCHLEA( ELEVATION IN ISOLATED SPIRAL GANGLION)

Intracellular calcium concentrations ([Ca2+](i)) in acutely isolated s piral ganglion cells (SGCs) of the guinea pig cochlea were measured us ing digital imaging microscopy and the Ca2+-sensitive fluorescence dye fura-2. L-glutamate increased [Ca2+](i) in SGCs with neuritic process es but did not lead to an increase in [Ca2+](i) in SGCs without neurit ic processes. The depolarization induced by high K+ (150 mM) solution increased [Ca2+](i) in both SGCs, with and without neuritic processes. The L-glutamate-induced [Ca2+](i) elevation was abolished in the abse nce of extracellular Ca2+. We thus propose that the increase of [Ca2+] (i) during L-glutamate stimulation is mainly related to an influx of e xtracellular Ca2+. The excitatory amino acids, probably L-glutamate, m ay function as a neurotransmitter of the hair cell-afferent nerve syna pse in the guinea pig cochlea.