title: Responses to apical and basolateral application of glutamate in mouse fungiform taste cells with action potentials.
abstract: In taste bud cells, glutamate may elicit two types of responses, as an umami tastant and as a neurotransmitter. Glutamate applied to apical membrane of taste cells would elicit taste responses whereas glutamate applied to basolateral membrane may act as a neurotransmitter. Using restricted stimulation to apical or basolateral membrane of taste cells, we examined responses of taste cells to glutamate stimulation, separately. Apical application of monosodium glutamate (MSG, 0.3 M) increased firing frequency in some of mouse fungiform taste cells that evoked action potentials. These cells were tested with other basic taste compounds, NaCl (salty), saccharin (sweet), HCl (sour), and quinine (bitter). MSG-sensitive taste cells could be classified into sweet-best (S-type), MSG-best (M-type), and NaCl or other electrolytes-best (N- or E/H-type) cells. Furthermore, S- and M-type could be classified into two sub-types according to the synergistic effect between MSG and inosine-5'-monophosphate (S1, M1 with synergism; S2, M2 without synergism). Basolateral application of glutamate (100 μM) had almost no effect on the mean spontaneous firing rates in taste cells. However, about 10% of taste cells tested showed transient increases in spontaneous firing rates (>mean + 2 standard deviation) after basolateral application of glutamate. These results suggest the existence of multiple types of umami-sensitive taste cells and the existence of glutamate receptor(s) on the basolateral membrane of a subset of taste cells.
authors.affiliation: Section of Oral Neuroscience, Graduate School of Dental Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.
authors.forename: Mayu
authors.initials: M
authors.lastname: Niki
authors.forename: Shingo
authors.initials: S
authors.lastname: Takai
authors.forename: Yoko
authors.initials: Y
authors.lastname: Kusuhara
authors.forename: Yuzo
authors.initials: Y
authors.lastname: Ninomiya
authors.forename: Ryusuke
authors.initials: R
authors.lastname: Yoshida
mesh_terms: D000200:Action Potentials / Q000187:drug effects* / Q000502:physiology*; D000818:Animals; D016764:Cell Polarity; D005260:Female; D005503:Food Additives / Q000494:pharmacology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D012970:Sodium Glutamate / Q000494:pharmacology*; D013649:Taste / Q000187:drug effects / Q000502:physiology; D013650:Taste Buds / Q000166:cytology* / Q000187:drug effects*
chemical_list: D005503:Food Additives; D012970:Sodium Glutamate