Ionic mechanism of generation of receptor potential in response to quinine in frog taste cell.

The ionic mechanism of generation of the receptor potential in a frog taste cell elicited by quinine-HCl (Q-HCl) was studied with an intracellular recording technique by replacing the superficial and interstitial fluids of the tongue with various saline solutions. The taste cells whose receptor membranes were adapted to normal saline and deionized water generated depolarizing receptor potentials at Q-HCl concentrations higher than 2 and 0.01 mM, respectively. The input resistance of taste cell during Q-HCl stimulation scarcely changed. The receptor potential did not change even when the membrane potential level was broadly changed. The magnitude of the receptor potential was increased by reducing the concentration of superficial Cl- on the taste receptor membrane, but was independent to the concentration of superficial Na+. Injection of Cl- into a taste cell increased the receptor potential to 170%. The magnitude of receptor potential was decreased to 20-30% by removing interstitial Na+ or Cl- or both surrounding the basolateral membrane of taste cell. Furosemide (1 mM) added to the interstitial fluid decreased the receptor potential to 15%, while interstitial ouabain (0.1 mM) and superficial SITS (0.1 mM) did not influence it. From these results, we conclude: (1) an electroneutral Na+/Cl- cotransport occurs through the basolateral membrane of a taste cell in the resting state, so that Cl- accumulates inside the cell. (2) Q-HCl stimulation induces the active secretion of Cl- across the taste receptor membrane, resulting in a depolarizing receptor potential.