Generation of Cyclic AMP in Taste Buds of the Rat Circumvallate Papilla in Response to Sucrose
Epithelial sheets rich in taste buds and free of muscle tissue and von Ebner’s washing glands were isolated as a U-shaped cleft which surrounds the circumvallate (CV) papilla of the rat tongue. The sheet of CV tissue from one tongue (total protein content: 8–14 µg) was cut in two approximately equal parts which were incubated with permeant phosphodiesterase inhibitor (IBMX; 0.3 mM) and 0 or 150–600 mM sucrose. After 6 min of incubation, the sheets were washed, the cells permeabilized and their cyclic AMP (cAMP) content determined by radioimmunoassay. Paired estimates with tissue from the same animal showed a significant sucrose-induced cAMP production (range 5–20 fmol/µg protein at 600 mM sucrose). This increase in intracellular cAMP was linearly dependent on the sucrose concentration and was suppressed by about 65% when 50 mM of a competitive antagonist of sucrose (methyl 4,6-dichloro-4,6-dideoxy-α-D-galactopyranoside) was added to the sucrose solution. Epithelial sheets free of taste buds did not respond to either sucrose or the inhibitor. These results are in line with previous suggestions that cAMP may be a second messenger in the transduction of sweet taste in the rat.