味覚の相乗効果発現機序に関する研究 : 味細胞内Caイオン濃度の変化を指標として(<特集>刺激受容における相互作用の発現機構のメカニズム)

概要

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It is well known that taste stimuli by amino acids and nucleosides can cause synergistic effects. It is also known that saccharin could cause augmentation of D-phenylalanine response. However, the mechanisms of these synergistic effects are unknown yet. To elucidate the underlying mechanism, we have assessed intracellular Ca^<2+> dynamics during combined taste stimuli by monosodium glutamate (MSG) and guanosine-5'-monophosphate (GMP) or inosine-5'-monophosphate (IMP) as well as by saccharin (Sac) and D-phenylalanine (D-Phe). Fura-PE3 were loaded in taste cells and temporal changes in [Ca^<2+>]_1 were assessed. Taste cells that responded to MSG by an increase in [Ca^<2+>]_1 also responded to IMP or GMP. Some of these cells exhibited synergistic [Ca^<2+>]_1 increases in responses to MSG+GMP/IMP. These [Ca^<2+>]_1 transients persisted under removal of extracellular Ca^<2+>, indicating that synergistic effect could be mediated by signal transduction systems coupled to Ca^<2+> released from intracellular stores. In addition, saccharin caused augmentation of D-phenylalanine-induced [Ca^<2+>]_1 increases, that was compatible with those previously suggested electrophysiologically.
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