The ionic mechanism underlying the receptor potential induced by a deionized water stimulus was studied in frog taste cells with conventional microelectrodes. The taste cells located in the proximal portion of the tongue generated a depolarizing receptor potential which averaged 10mV in response to stimulation with deionized water. The cell membrane of the water-sensitive taste cell could be divided into the taste-receptive (apical) and basolateral membranes and the cells were classified into two types: Cl(-)-dependent and Cl(-)-independent. In Cl(-)-dependent cells whose input resistance was decreased or unchanged by deionized water, the magnitude of the water-induced depolarization decreased with an increase in concentration of superficial Cl- in contact with the receptive membrane and with addition of blockers of anion channels (0.1 mmol l-1 SITS and 0.1 mmol l-1 DIDS) to deionized water. The reversal potential for the depolarization in this type shifted according to the concentration of superficial Cl-. These properties of the responses were consistent with those of the glossopharyngeal nerve which innervates the taste disc. In Cl(-)-independent cells whose input resistance was increased by deionized water, the reversal potential was approximately equal to the equilibrium potential for K+ at the basolateral membrane. The water-induced response of the glossopharyngeal nerve was decreased to about 60% of the control value by addition of interstitial 2 mmol l-1 Ba2+. It is concluded that the water-induced receptor potential is produced by Cl- secretion through the taste-receptive membrane in about 70% of water-sensitive frog taste cells, while it is generated by an inhibition of the resting K+ conductance of the basolateral membrane in the remaining 30% of the cells.

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