Mechanism of the water response in frog gustation: possible significance of surface potential.

The frog taste response to deionized water (water response) after adaptation of the tongue to salts was recorded from the glossopharyngeal nerve under various conditions. It was found that the frog water response exhibits different behavior from the carp water response examined in a previous paper13. (a) The frog water response did not decline during stimulation and lasted for at least 3 min, while the carp water response declined within 10 s after stimulation to a spontaneous level. (b) The frog water response was practically independent of species and concentrations of salts in adapting solutions when the tongue was adapted to salts of monovalent cations, while the carp water response was highly dependent of salt concentration in adapting solution. (c) The water response was increased with an increase of CaCl2 concentration in adapting solution, while it was decreased with an increase of MgCl2 concentration. (d) The water response was suppressed by the presence of electrolytes in stimulating solution: the data obtained with different species of salts were described by a single curve as a function of the ionic strength. (e) The mechanism of the frog water response together with the carp water response was explained in terms of the surface potential.