COUPLING OF BITTER RECEPTOR TO PHOSPHODIESTERASE THROUGH TRANSDUCIN IN TASTE RECEPTOR-CELLS

THE rod and cone transducins rue specific G proteins originally though t to be present only in photoreceptor cells of the vertebrate retina(1 -4). Transducins convert light stimulation of photoreceptor opsins int o activation of cyclic GMP phosphodiesterase (reviewed in refs. 5-7). A transducin-like G protein, gustducin, has been identified and cloned from rat taste cells(8). We report here that rod transducin is also p resent in vertebrate taste cells, where it specifically activates a ph osphodiesterase isolated from taste tissue. Furthermore, the bitter co mpound denatonium in the presence of taste-ceh membranes activates tra nsducin but not G(i). A peptide that competitively inhibits rhodopsin activation of transducing also blocks taste-cell membrane activation o f transducin, arguing for the involvement of a seven-transmembrane-hel ix G-protein-coupled receptor. These results suggest that rod transduc in tranduces bitter taste by coupling taste receptor(s) to taste-cell phosphodiesterase. Phosphodiesterase-mediated degradation of cyclic nu cleotides may lead to taste-cell depolarization through the recently i dentified cyclic-nucleotide-suppressible conductance(10).