al.: Trpm5 null mice respond to bitter, sweet, and umami compounds. Chem Senses 2006

Trpm5 is a calcium-activated cation channel expressed selectively in taste receptor cells. A previous study reported that mice with an internal deletion of Trpm5, lacking exons 15–19 encoding transmembrane segments 1–5, showed no taste-mediated responses to bitter, sweet, and umami compounds. We independently generated knockout mice null for Trpm5 protein expres-sion due to deletion of Trpm5#s promoter region and exons 1–4 (including the translation start site). We examined the taste-mediated responses of Trpm5 null mice and wild-type (WT) mice using three procedures: gustatory nerve recording [chorda tympani (CT) and glossopharyngeal (NG) nerves], initial lick responses, and 24-h two-bottle preference tests. With bitter com-pounds, the Trpm5 null mice showed reduced, but not abolished, avoidance (as indicated by licking responses and preference ratios higher than those of WT), a normal CT response, and a greatly diminished NG response. With sweet compounds, Trpm5 null mice showed no licking response, a diminished preference ratio, and absent or greatly reduced nerve responses.With umami compounds, Trpm5 null mice showed no licking response, a diminished preference ratio, a normal NG response, and a greatl