GENERATION OF INOSITOL PHOSPHATES IN BITTER TASTE TRANSDUCTION

It is probable that there is a diversity of mechanisms involved in the transduction of bitter taste. One of these mechanisms uses the second messengers, inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DA G). Partial membrane preparations from circumvallate and foliate taste regions of mice tongues responded to the addition of known bitter tas te stimuli by increasing the amount of inositol phosphates produced af ter 30 s incubation. Addition of both the bitter stimulus, sucrose oct aacetate and the G-protein stimulant, GTP gamma S, led to an enhanced production of inositol phosphates compared with either alone. Pretreat ment of the tissue samples with pertussis toxin eliminated all respons e to sucrose octaacetate plus GTP gamma S, whereas pretreatment with c holera toxin was without effect. Western blots of solubilized tissue f rom circumvallate and foliate regions probed with antibodies to the al pha-subunit of several types of G-proteins revealed bands reactive to antibodies against G alpha(i1-2), and G alpha(0),, with no apparent ac tivity to antibodies against G alpha(i3). Given the results from the i mmunoblots and those of the toxin experiments, it is proposed that the transduction of the bitter taste of sucrose octaacetate in mice invol ves a receptor-mediated activation of a G(i)-type protein which activa tes a phospholipase C to produce the two second messengers, IP3 and DA G.