The Contribution of SERCA to Taste Perception compounds denatonium (left) and quinine (right) indicated the significantly increased nerve responses to 0.1 mM denatonium and 0.3 mM quinine obtained from Serca3 KO mice (filled squares) compared with those of WT mice (open circles). (C) Integrated neural responses, such as those shown in (A), were normalized to the response elicited by 0.1 M NH4Cl. No significant difference in the nerve responses to sweet, umami, sour, and salty tastes is apparent between WT mice (open bars) and KO mice (filled bars). Data are means 6 SEMs (n = 6–8). Mixed-model ANOVA and post hoc t-tests were performed (**p,0.01). doi:10.1371/journal.pone.0023165.g007 Immunocytochemical results indicated that, unlike immunostain- ing with Serca3 antibody, which was distributed throughout the taste cell body, Serca2 staining was punctuate and localized to limited cytoplasmic regions, in many cases the area apical to the nucleus (Fig. 8). To determine which types of taste cells express Serca2, we performed double-label immunohistochemistry on rat CV taste epithelia with antibody to Serca2 along with the antibodies recognizing Trpm5, a-gustducin, or T1R3 protein. Since the anti-Serca2 antibody was generated in mice, we used taste tissue sections from rat instead of mouse to eliminate possible intrinsic background staining in the mouse tissue. We found that (1) Trpm5 and Serca2 signals were largely overlapping, but a few cells expressed Trpm5 only; (2) many cells expressed both Serca2 and a-gustducin, but some cells expressed only one or the other; and (3) nearly all Serca2-expressing cells expressed T1R3 (Fig. 8). Together, these data indicate that Serca2 is expressed mainly in a subpopulation of Trpm5/T1R3-expressing cells, suggesting that it is likely to contribute to sweet and umami taste sensation. Discussion In this study, we performed transcriptomic screen of single taste bud cells by subtracting cDNA of type I cells from that of TRCs to facilitate the isolation of genes specifically or more abundantly expressed in TRCs than in type I taste bud cells. Among these differentially expressed genes, we identified Serca3, a member of SERCA family that encodes a molecular pump known to actively transport Ca2+ from the cytosol into the ER. Three genes, ATP2A1, 2, and 3, encode SERCA 1, 2, and 3 transcripts, which produce various isoforms in a species-, tissue-, and developmental stage-specific manner [43]. In taste tissue of adult rodents, we used splice variant-specific PCR primers and detected transcripts for all known Serca3 variants: two rat variants (Serca3a and 3b/c) and three mouse variants (Serca3a, 3b, and 3c). With the primers covering the entire coding sequences, we also isolated the transcripts for all variants except mouse Serca3c, and as the variant-specific PCR data (Fig. 1) indicated, the failure to amplify Figure 8. Serca2 is expressed in sweet and umami taste receptor cells. Rat circumvallate papilla sections were double immunostained with anti-Serca2 antibody (green) and with antibodies against Trpm5 (left panels), a-gustducin (middle panels), or T1R3 (right panels) (red). Overlay of the immunofluorescence images (bottom row) showed that Serca2 was expressed mainly in a subpopulation of Trpm5/T1R3-expressing cells, and, to a lesser extent, in a-gustducin-expressing cells. Scale bars, 25 mm. doi:10.1371/journal.pone.0023165.g008 PLoS ONE | www.plosone.org 8 August 2011 | Volume 6 | Issue 8 | e23165