Joint Study on Mechanisms of Umami Perception : Analyzes of the responses of taste cells to monosodium glutamate

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Monosodium glutamate (MSG) elicits a unique taste called umami. Whole-cell patch-clamp recordings from taste cells isolated from mouse vallate and foliate taste buds have indicated that MSG elicits several different types of responses, suggesting that multiple pathways may be involved in umami taste. We have also used fluorescent dyes and digital imaging techniques to measure MSG-evoked changes in membrane potential and intracellular calcium in taste cells from C3H mice. In this study, similar imaging techniques were used to record the responses of vallate and foliate taste cells from B6 mice to MSG (10 mM), the metabotropic receptor agonist, L-AP4 (2-amino-4-phosphonobutyrate)(1 mM) and the ionotropic receptor agonist, NMDA (1 mM). And we examined the responses of isolated mouse taste cells to MSG or L-AP4, by using whole-cell patch-clamp technique. The results suggest that MSG perception mediates via metabotropic glutamate receptor 4(mGluR 4) that decreases a membrane conductance, an … More d/or another receptor type that increases a membrane conductance. Cells in isolated taste buds were doubly stained with the voltage-sensitive dye, di-8-ANNEPS,and the Ca^<2+>-sensitive dye, fura-2. Since mGluR4 receptors in the CNS have been shown to activated Gi, blocked K channels and depolarize the cells, we examined the effect of the K channel blocker, tetraethyl ammonium (TEA), on taste cells responses. Addition of TEA (10 mM) to the bath solution resulted in membrane depolarization in about half of the taste cells. In addition, TEA markedly reduced the number of taste cells showing increases in [Ca]i in response to MSG and L-AP4. In contrast, the number of taste cells displaying responses to NMDA was not reduced by TEA.In the absence of TEA,approximately half of the cells displayd changes in membrane potential when stimulated with L-AP4. In the presence of TEA,membrane potential changes were elicited by L-AP4. These results are consistent with previous patch-clamp data suggesting that MSG activates several different mechanisms in taste cells, including processes mediated by ionotropic and metabotropic types of receptors. Less