Bitter taste transduced by PLC-β2-dependent rise in IP3 and α-gustducin-dependent fall in cyclic nucleotides

Current evidence points to the existence of multiple processes for bitter taste transduction. Previous work demonstrated involvement of the polyphosphoinositide system and an α-gustducin (Gα gust )-mediated stimulation of phosphodiesterase in bitter taste transduction. Additionally, a taste-enriched G protein γ-subunit, Gγ 13 , colocalizes with Gα gust and mediates the denatonium-stimulated production of inositol 1,4,5-trisphosphate (IP 3 ). Using quench-flow techniques, we show here that the bitter stimuli, denatonium and strychnine, induce rapid (50–100 ms) and transient reductions in cAMP and cGMP and increases in IP 3 in murine taste tissue. This decrease of cyclic nucleotides is inhibited by Gα gust antibodies, whereas the increase in IP 3 is not affected by antibodies to Gα gust . IP 3 production is inhibited by antibodies specific to phospholipase C-β 2 (PLC-β 2 ), a PLC isoform known to be activated by Gβγ-subunits. Antibodies to PLC-β 3 or to PLC-β 4 were without effect. These data suggest a transduction mechanism for bitter taste involving the rapid and transient metabolism of dual second messenger systems, both mediated through a taste cell G protein, likely composed of Gα gust /β/γ 13 , with both systems being simultaneously activated in the same bitter-sensitive taste receptor cell.