Values shown are mean s.e.m.; significance in t-tests was determined by applying the Bonferroni correction for 4 comparisons.D.The PKC inhibitor, bisindolymaleimide I (Bis; 0.15 M) did not influence Ca2+responses to denatonium. C2 (PLC2) [5,6] to produce inositol trisphosphate (IP3) and activate the type 3 IP3receptor, IP3R3 [7,8] to release stored Ca2+. Mice in which these effector genes are knocked out show taste afferent nerve and Granisetron behavioral responses to sweet, bitter and umami stimuli that are either eliminated in the case of PLC2, [6], or compromised in the case of IP3R3, [9]. These findings underline the central functions of PLC2 and IP3R3 in taste transduction. G-gustducin (-gus) [10] is usually a frequent partner of G313 and Gus-/-mice are compromised to bitter, nice, and umami stimuli [11]. Yet, despite its discovery over 15 years ago, the precise role of -gus in taste Granisetron transduction is still unclear. As with the closely related G-transducins, effector-interacting peptides derived from -gus can activate a retinal PDEin vitroto decrease cyclic nucleotide levels [12,13]. We considered the possibility that -gus in taste cells may regulate cAMP levels in a continuous fashion, in the absence of taste ligands. If this were the Retn case, genetic ablation of -gus should markedly alterbasallevels of cAMP in taste cells. We directly tested this hypothesis by measuring cAMP levels in taste buds of -gus+/+and -gus-/-mice. We selected circumvallate (CV) taste buds for this analysis because (a) taste buds are numerous, (b) earlier studies linking gus to bitter transduction were performed in CV and (c) -gus couples primarily to bitter receptors in this taste field [1]. We show that taste buds of -gus-/-mice have highly elevatedbasallevels of cAMP relative to those in -gus+/+mice. Further, we show in taste buds from -gus-/-mice, that elevated cAMP in -gus-lineage cells activates cAMP-dependent Protein Kinase A (PKA) Granisetron causing a chronic inhibition of Ca2+responses to bitter stimuli. Our data lead us to propose a novel explanation of the -gus knockout phenotype. We suggest that taste buds in -gus-/-mice exist in a chronically stressed out state, unable to generate strong release of stored Ca2+in response to any of the taste GPCR-mediated taste qualities. == 2. MATERIALS AND METHODS == == Animals == Mouse housing and experimental procedures were approved by Colorado State Universitys Animal Care and Use Committee. Animals were killed by exposure to CO2followed by cervical dislocation before tongues were removed. Adult -gus-/-mice [11] and -gus+/+littermates were utilized for cAMP measurements. For Ca2+imaging experiments, transgenic mice in which the -gus promoter drives expression of GFP, i.e. gus-GFP [4], were crossed with -gus-/-mice. GFP-positive, -gus-negative progeny were recognized. In these mice, taste cells of the -gus lineage express the GFP label, while lacking -gus itself. == Physiological solutions and reagents == Tyrodes answer contained (in mM): 140 NaCl, 5 KCl, 1 MgCl2, 1 CaCl2, 10 HEPES, 10 glucose, and 1 pyruvate (pH 7.4 with NaOH). Calcium-Magnesium-free (CMF) Tyrodes solution was similar to the above except Granisetron that MgCl2and CaCl2were omitted (i.e. nominally CMF) or were replaced with 1 mM BAPTA for isolating taste buds. The PKA inhibitor, H-89, and the Protein Kinase C (PKC) inhibitor, bisindolymaleimide I (Bis, Calbiochem; San Diego) were diluted from dimethyl sulfoxide stocks into Tyrodes solution before use. == cAMP measurements == Taste bud-enriched CV epithelia from -gus-/-and -gus+/+mice were enzymatically delaminated, dissected free of adjacent non-taste epithelium, and were processed in parallel as we described previously [14,15]. Tissues were lysed to extract cAMP into a soluble supernatant and total cAMP in each tissue extract was measured using enzyme immunoassay (Amersham Biosciences, Piscataway, NJ) [14,15]. Total protein in each tissue piece was quantified using Granisetron a Nano-Orange Kit (Invitrogen,.