Stimulus-induced currents in isolated taste receptor cells of the larval tiger salamander

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Abstract
Gustatory receptor cells, isolated from the lingual epithelium of larval tiger salamanders (Ambystoma tigrinum), possess a variety of voltage- and ion-dependent conductances, including a transient Na+ -current (INa), a voltage-gated Ca2+ -current (IA). a transient K+ -current (IA), a delayed rectifier K+ -current (IK), and a Ca2+ -activated K+ -current (IK(Ca))- By use of whole-cell and excised-patch tight-seal recording techniques, we examined the effects of taste stimuli on the conductances of taste cells from the tiger salamander. Depolarizing receptor potentials elicited by NaCl were associated with slow, graded inward currents which were composed of amiloride-sensitive and tetrodoxin-(TTX)-sensitive components. Potassium chloride produced maintained inward currents, which usually showed both phasic and tonic components and were only partially blocked by tetraethylammonium chloride (TEA). Citric and acetic acids elicited slow depolarizations in taste cells. Under voltage-clamp, acids produced graded inward currents which were composed of two components: one attributable to a transient block of voltage-dependent K+ -channels and a smaller component which may have resulted from an increased conductance to cations. Quinine hydrochloride elicited slow depolarization of taste cells which was associated with a slowly developing maintained inward current under voltage-clamp. Quinine suppressed both voltage-dependent inward and outward currents. In some taste cells, L-arginine elicited small outward currents which were attributable to an increase in K+ conductance. In other cells, L-arginine produced a decrease in voltage-dependent outward currents and generated depolarizations associated with inward currents. These results indicate that several independent mechanisms, including amiloride-sensitive Na+ -channels, and stimulus modulation of voltage-dependent K+ -channels, are involved in taste cell responses to chemical stimuli. More than one mechanism is typically present in a single cell.

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