Behavioral evidence for a role of α-gustducin in glutamate taste

Abstract

The taste perception of monosodium glutamate (MSG) is termed 'umami'. Two putative taste receptors for glutamate have been identified, a truncated form of mGluR4 (taste-mGluR4) and the presumed heterodimer T1R1 + T1R3. Both receptors respond to glutamate when expressed in heterologous cells, but the G protein involved is not known. Gα-Gustducin mediates the transduction of several bitter and sweet compounds; however, its role in umami has not been determined. We used standard two-bottle preference tests on α-gustducin knockout (KO) and wildtype (WT) mice to compare preferences for ascending concentrations of MSG and MSG + 5′-inosine monophosphate (IMP). A Latin Square was used to assign the order of tastants presented to each mouse. Statistical comparisons between KO and WT mice revealed that whereas WT mice preferred solutions of MSG and MSG + IMP over water, KO mice showed little preference for these stimuli. Denatonium and sucrose served as control stimuli and, as shown previously, WT mice prefered sucrose and avoided denatonium significantly more than did KO mice. Naïve mice were also tested, and while prior exposure to taste stimuli influenced the magnitude of the preferences, experience did not change the overall pattern of intake. These data suggest that α -gustducin plays a role in glutamate taste. © Oxford University Press 2003; all rights reserved.