The Contribution of SERCA to Taste Perception Figure 3. Serca3 protein is found in Trpm5- but not Gad1-expressing cells. Confocal images of CV taste papillae sections show the fluorescence of GFP(green, left) expressed under the control of Trpm5 (upper panels) or Gad1 (lower panels) promoters, labeling sweet/umami/bitter TRCs and most presynaptic cells, respectively, and the immunostaining with the anti-Serca3 antibody (red, center panels). The merged images show near-perfect overlap (yellow-orange) in Trpm5-GFP mice (upper right) but no overlap in Gad1-GFP mice (lower right). Scale bars, 25 mm. doi:10.1371/journal.pone.0023165.g003 Increased gustatory nerve responses to bitter tastants in Serca3 KO mice To determine whether the augmented behavioral responses of Serca3 KO mice to bitter compounds were attributable to the deficiency in the peripheral gustatory system, we performed electrophysiological recordings of the gustatory nerve with taste stimuli. We recorded from the glossopharyngeal nerve since it innervates taste buds in the posterior part of the tongue, in which the bitter taste receptors are more abundantly expressed [13]. Consistent with the behavioral data described above, the nerve responses in Serca3 KO mice to bitter taste stimuli (denatonium and quinine) were significantly increased compared with those of the WT mice (Fig. 7, Table S4). In contrast, we observed no significant differences between KO mice and WT mice in the nerve responses to sweet, umami, sour, and salty tastes (Fig. 7A and C, Table S4). Figure 4. Normal taste bud morphology and expression of taste-signaling molecules in Serca3 KO mice. Immunofluorescence images of Serca3-KO mouse circumvallate taste tissue sections with antibodies against Serca3, T1R3, a-gustducin, PLCb2, Trpm5, and neural cell adhesion molecule (NCAM) indicate that Serca3 protein was absent in taste buds, whereas the expression of other proteins appeared unaltered. Scale bars, 25 mm. doi:10.1371/journal.pone.0023165.g004 PLoS ONE | www.plosone.org 4 August 2011 | Volume 6 | Issue 8 | e23165