ON THE “WATER RESPONSE” OF FROG'S TONGUE

1. In order to study the mechanism of the “water response” of frog's tongue, the response of the receptors connected with a large nerve fibre was examined using common Japanese frog. 2. Frog's tongue appeared to contain receptors sensitive to tap water, but the receptors were not observed to respond to distilled water in Ca-free conditions. 3. The threshold concentration of the receptors for calcium ions appeared to be less than 0.05 mM, and the magnitude of the response to tap water was similar to that to the CaCl2 solutions having a similar calcium concentration to tap water. 4. The receptors responded to monovalent cations as well as to divalent cations, but the threshold concentration for monovalent cations was very high, compared with that for calcium ions. 5. The response to calcium ions was inhibited by monovalent cations added to the test solutions. And it was suggested that the inhibitory effect of sodium ions on the response to calcium ions is due to a competitive action of sodium and calcium ions for the receptor site of the cell membrane.