Phasic and tonic components of gustatory response in the frog

Abstract

Characteristics of phasic and tonic responses of the frog glossopharyngeal nerve to various salts were examined under a variety of conditions. The results obtained are summarized as follows: 1) The salt concentration of adapting solutions affected greatly the phasic component of the responses to NaCl, KCl, MgCl2, and CaCl2, whereas the tonic component was independent of the adapting condition. 2) Either the phasic or tonic component was preferentially suppressed under appropriate conditions. 3) An abrupt rise of temperature of stimulating solution produced a phasic response. Magnitude of the phasic response induced by a rise of temperature was a function of both species and concentration of salts in the stimulating solution. 4) Binding of Hg2+ to the receptor and elimination of the bound Hg2+ by mercaptoethanol gave similar large phasic response. A slow elimination of the bound Hg2+ led to no response. It was concluded that a phasic response appears only when environments such as salt concentration or temperature are changing and that its magnitude is related to the rate of changes, whereas a tonic response represents information of the receptor membrane in an equilibrium state. Discussion on the obtained results was made under an assumption that the phasic response is attributed to a dynamic conformational change of the receptor membrane.