[Epithelial response of the frog tongue surface to salt and its relation to taste nerve activity]

This study demonstrated the electrophysiological characteristics of the dorsal surface of the frog tongue in vivo. The results were as follows: 1. Epithelial potential of the tongue surface was abolished with respect to the grounded leg muscle when the tongue was adapted to 30 mM NaCl solution among various NaCl concentrations. In the 30 mM NaCl-adaptation, magnitude of integrated impulse discharges simultaneously obtained from the glossopharyngeal nerve was lowest. Thus, this solution was mainly used as the adapting solution during the experiments. 2. Stimulation of the tongue with NaCl, acetic acid, quinine-HCl, and sucrose produced changes in the epithelial potential and the integrated impulse discharges (epithelial and neural response, respectively). Both responses showed inherent patterns to the stimulus quality and concentration. 3. The epithelial response to NaCl was negative to the ground, and its magnitude was increased with decreasing NaCl in the adapting solution and decreased with increasing NaCl. These influences were similar to those of the neural response. 4. The relationship between the epithelial response and the stimulus NaCl was in approximate agreement with that of the neural response. 5. Characteristics of the epithelial response to NaCl coincided with those obtained from the isolated dorsal epithelium of the tongue in vitro, which were associated with a decrease in resistance across the tissue. 6. Ouabain had no influence on both the epithelial and neural responses to NaCl, but local anesthetics reversibly inhibited them. The inhibition by local anesthetics was slower and smaller in the epithelial response than in the neural response. 7. Salts similar to NaCl also produced epithelial and neural responses, but their magnitudes inversely depended on an inherent hydrated cation size of the salts in aqueous solution. Based on the results, it is concluded that the epithelial response to NaCl is produced by sodium transport across the dorsal epithelium of the tongue, and the transport may relate to the mechanism of salty sensation.