Changes in outward K+ currents in response to two types of sweeteners in sweet taste transduction of gerbil taste cells.

Using the whole cell patch clamp technique, we measured changes in outward K+ currents of gerbil taste cells in response to different kinds of sweeteners. Outward K+ currents of the taste cell induced by depolarizing pulses were suppressed by sweet stimuli such as 10 mM Na-saccharin. The membrane-permeable analog of cAMP, cpt-cAMP, also decreased outward K+ currents. On the other hand, the K+ currents were enhanced by amino acid sweeteners such as 10 mM D-tryptophan. The outward K+ current was enhanced by external application of Ca(2+)-transporting ionophore, 5 microM ionomycin, and intracellular application of 5 microM inositol-1,4,5-trisphosphate (IP3). The outward K+ currents were no longer suppressed by 10 mM Na-saccharin containing 20 microM gurmarin, but were still enhanced by 10 mM D-tryptophan containing 20 microM gurmarin. These results suggest that sweet taste transduction for one group of sweeteners such as Na-saccharin in gerbils is concerned with an increase of the intracellular cAMP level, and that the transduction for the other group of sweeteners such as D-tryptophan is concerned with an increase of the intracellular IP3 level which releases Ca2+ from the internal stores.