RAPID KINETICS OF 2ND-MESSENGER PRODUCTION IN BITTER TASTE

The tasting of bitter compounds may have evolved as a protective mecha nism against ingestion of potentially harmful substances. We have iden tified second messengers involved in bitter taste and show here for th e first time that they are rapid and transient. Using a quench-flow sy stem, we have studied bitter taste signal transduction in a pair of mo use strains that differ in their ability to taste the bitter stimulus sucrose octaacetate (SOA); however, both strains taste the bitter agen t denatonium. In both strains of mice, denatonium (10 mM) induced a tr ansient and rapid increase in levels of the second messenger inositol 1,4,5-trisphosphate (IP3) with a maximal production near 75-100 ms aft er stimulation. In contrast, SOA (100 mu M) brought about a similar in crease in IP3 only in SOA-taster mice. The response to SOA was potenti ated in the presence of GTP (1 mu M) The GTP-enhanced SOA-response sup ports a G protein-mediated response for this bitter compound. The rapi d kinetics, transient nature, and specificity of the bitter taste stim ulus-induced IP3 formation are consistent with the role of IP3 as a se cond messenger in the chemoelectrical transduction of bitter taste.