Transduction mechanism of four basic taste stimuli into electric signals of taste cell

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1. The purpose of this project is to clarify the mechanisms underlying the generation of receptor potential of the taste cell in response to the four taste stimuli.2. The in situ frog tongues were used and intracellular receptor potentials were recorded from single taste cells of the fungiform papillae by inserting a 3 M KCl-filled microelectrode into the cell. As the four basic taste stimuli, 0.5 M NaCl, 1 mM HCl, 10 mM quinine-HCl (Q-HCl) and 1 M garactose were used.3. The receptor potential for NaCl was greatly reduced by removing mono- and divalent cations from the superficial fluid over the tongue and <Na^+> from the interstitial fluid surrounding taste cells. Therefore it is concluded that the NaCl-induced receptor potential is generated by ionic currents flowing cation-selective channel of the receptor membrane and <Na^+> channel of the basolateral membrane.4. The receptor potential for HCl was not affected by interstitial ions, but was greatly depressed by removing <Ca^(2+)> and <Na^+> in the superficial fluid and by adding furosemide to it. Even after adaptation of the tongue to water, large acid response was evoked. Therefore, the large portion of the HCl-induced response is generated by <Ca^(2+)> channel of the receptor membrane but the remaining portion is generated by the phase boundary potential.5. The receptor potential for Q-HCl was greatly increased by reducing <Cl^-> in the superficial fluid and was reduced by removing <Na^+> and <Ca^(2+)> and adding furosemide in the interstitial fluid. Therefore, the most of the Q-HCl response is generated by a release of <Cl^-> accumulated by a <Na^+> / <Cl^-> cotransport.6. The receptor potential for galactose was greatly reduced by removing <Cl^-> and adding DCCD in the interstitial fluid and increased by reducing a pH of superficial fluid. Thus it is suggested that the galactose response is generated by a release of <OH^-> which is related to <Cl^-> -dependent <H^+> pump.