Glycine induced calcium concentration changes in vestibular type I sensory cells.
Glutamate is the neurotransmitter of the synapse between vestibular type I hair cells and the afferent nerve calyx. This calyx may also be involved in local feedback, which may modify sensory cell activity via N-methyl-D-aspartate (NMDA) receptors. Glycine is the co-agonist of glutamate in NMDA receptor activation. Both agents have been detected by immunocytochemistry in the nerve calyx. Glutamate and NMDA stimulations cause changes in the intracellular calcium concentration ([Ca(2+)](i)) of isolated type I sensory cells. We investigated the effect of glycine stimulation on [Ca(2+)](i) in guinea pig type I sensory cells by spectrofluorimetry with fura-2. Glycine application to isolated type I sensory cells induced a rapid and transient increase in [Ca(2+)](i). The fluorescence ratio increased by 55% above the resting level. The peak was reached in 9 s and the return to basal level took about 20 s. A specific antagonist of the glycine site on NMDA receptors, 7-chlorokynurenate (10 microM), decreased the calcium response to glycine by 60%. Glycine may activate NMDA receptors. Glycine may also activate the strychnine-sensitive glycine receptor-gated channel. Strychnine (50 microM) decreased the calcium response to glycine by 60%. Thus, glycine probably induces calcium concentration changes in type I vestibular sensory cells via NMDA receptors and/or glycine receptors.
Devau
G
G
INSERM U432, Université Montpellier II, place Eugène Bataillon, 34095, Montpellier, France. gdevau@univ.montp2.fr
D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002614:Chelating Agents / Q000494:pharmacology; D002712:Chlorides / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D005971:Glutamates / Q000494:pharmacology; D005998:Glycine / Q000494:pharmacology*; D006168:Guinea Pigs; D018069:Hair Cells, Vestibular / Q000187:drug effects* / Q000378:metabolism; D007736:Kynurenic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D008959:Models, Neurological; D016202:N-Methylaspartate / Q000494:pharmacology; D013331:Strychnine / Q000494:pharmacology
D002614:Chelating Agents; D002712:Chlorides; D018690:Excitatory Amino Acid Agonists; D018691:Excitatory Amino Acid Antagonists; D005971:Glutamates; D004533:Egtazic Acid; D016202:N-Methylaspartate; D007736:Kynurenic Acid; D013331:Strychnine; C057013:7-chlorokynurenic acid; D002118:Calcium; D005998:Glycine