Stimulation of the gerbil's gustatory receptors by saccharin.

The gustatory responses from the chorda tympani nerve of the Mongolian gerbil, Meriones unguiculatus, were tested with saccharin and some closely related compounds. Only two compounds, saccharin and 6-chlorosaccharin, stimulated the gerbil's taste receptors to any degree and in the same order in which they are sweet to man, saccharin greater than 5-chlorosaccharin. Those compounds which are tasteless to man did not stimulate and include N-methyl saccharin, phthalimide, and O-sulfobenzoic acid. These nonstimulating derivatives did not inhibit the saccharin electrophysiological response. The saccharin taste response pH optimum is from 5 to 8. At pH 7 and 8, saccharin is fully ionized and is binding to the receptor site by an anionic mechanism. Kinetic plots of the taste response at pH 7 indicate that saccharin is forming 1:1 complexes with it. In addition, mixtures of saccharin and sucrose stimulate in such a manner as to suggest that they are interacting at different receptor sites.