Abstract
Umami taste, the taste of amino acids such as L-glutamate, is a pleasant gustatory sensation for the detection of protein and amino acids contents in foods. A number of G-protein coupled receptors have been proposed as umami receptor, including T1r1/T1r3 hetero dimmer, taste mGluR4 and taste mGluR1. In addition, transduction of umami has been shown to involve many intracellular signaling components. In the mouse chorda tympani nerve, there are at least 4 types of fibers responding to glutamate, suggesting multiple reception and transduction mechanisms for umami taste. In this study, we examined umami taste response of mouse fungiform taste cells. The apical restricted stimulation of monosodium glutamate (MSG) induced an increase in firing frequency in some taste cells. These cells were primarily divided into 2 groups. One responded best to sweeteners (S-group) and the other responded best to MSG (M-group). Taste cells in both groups were further classified into 2 groups according to the synergism between MSG and inosin-5'-monophosphate (IMP). One showed the robust synergism (S1 and M1) and the other did not (S2 and M2). These results were consistent with those of mouse chorda tympani nerve fibers, suggesting existence of multiple reception and transduction mechanisms for umami taste and selective signal transmission from taste cells to gustatory nerve fibers. Supported by JSPS Grants-in-Aid 18077004, 18109013 (YN) and 17791325 (RY). [J Physiol Sci. 2007;57 Suppl:S103]
