Observations of intracellular Ca^<2+> and Cl-concentrations in inner ear isolated cells

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1) To elucidate efferent inhibitory mechanisms of the cochlear hair cells and vestibular hair cells, the effects of candidate efferent neurotransmitters on intracellular Ca^<2+> concentrations ([Ca^<2+>] i) in these isolated cells of guinea pig were determined. Both Ach and ATP seem to be efferent neurotransmitters, however, CGRP and Enk were thought to be functioning as efferent neuromodulators.2) Slow shortening of cochlear outer hair cells has been speculated to modify cochlear sensitivity. Tetanic electrical field stimulation of isolated outer hair cells from guinea pigs shortened the cells for 2-3 min. Electrical stimulation reduced cell length and volume and decreased the intracellular Cl-concentration. These findings suggest that these shortening and shrinkage result from Cl- efflux.3) [Ca^<2+>] i is isolated spiral ganglion cells (SGCs) of the guinea pig cochlear were measured using the Ca^<2+> sensitive fluorescence dye fura-2. L-gultamate increased [Ca^<2+>] i in SGCs with neuritic processes. We thus propose that the excitatory amino acid, probably L-gultamate, may function as a neurotransmitter of the hair cell-afferent nerve synapse in the guinea pig cochlea.