Molecular mechanism of gustatory transduction in taste cells

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1. We investigated kinds of ionic channels and pumps and the gustatory transduction mechanisms in frog taste cells with electrophysiological techniques.2. We found voltage-gated Na channel and four types of K channels (Ca-activated ; delayed rectifier ; transient ; inward rectifier) in the taste cell membrane.3. Transduction of NaCl into a frog taste cell response is concerned with cation and anion channels of the apical receptive membrane and TTX insensitive Na channel of the basolateral membrane.4. Transduction of quinine-HCl into a frog taste cell response is concerned with a release of intracellular Cl^- through the apical receptive membrane.5. Transduction of galactose into the taste cell response is concerned with a release of intracellular OH^- or an entry of superficial H^+ or both through the apical receptive membrane.6. Transduction of HCl into the taste cell response is not concerned with channels and pumps at the basolateral membrane, but with Ca channels and proton pumps at the apical receptive membrane. The contribution of the former is much larger than that of the latter, and blocking the Ca channels with Cd^<2+> greatly reduced the acid-induced receptor potential.7. By simultaneous current recording and gustatory stimulation of the taste receptor membrane with a patch pipette, it was found that transduction of NaCl stimuli into the taste cell response is concerned with the NaCl-gated K^+ channels having a relatively low selectivity to monovalent cations.