Dual pathways for sweet taste transduction in isolated gerbil taste cells: cAMP and IP₃ mediated mechanisms

Abstract

Mechanisms of sweet taste transduction in gerbil taste cells were examined using the conventional whole-cell patch-clamp technique. Outward K⁺ currents of the taste cell induced by depolarizing electric pulses were reduced by 10 mM Na-saccharin, but were enhanced by amino acid sweeteners of 10 mM D-tryptophan. The outward K⁺ current was also enhanced by external application of Ca²⁺ -ionophore, 5μM ionomycin and intracelluar application of 5μM IP₃, (inositol-1, 4, 5-trisphosphate). These results suggest that the sweet taste transduction mechanism for Na-saccharin is concerned with an increase of the intracellular cAMP level, while that for D-tryptophan is concerned with an increase of the intracellular IP₃, level causing Ca₂₊ release from the internal stores. Gurmarin, an inhibitor of sweet taste. antagonized the suppressive effect of Na-saccharin on outward K⁺ currents, but did not affect the enhancing effect of Dtryptophan on outward K⁺ currents. The results from treatment with gurmarin suggest that the receptor site for Na-saccharin is different from that for D-tryptophan.