Abstract: | Inhibition of chorda tympani nerve responses to sugars and aminoacids by CuCl2 and ZnCl2 was studied in ddy mice. Responsesto sugars (sucrose, fructose, glucose and maltose) and Na saccharinwere markedly depressed after adaptation of the tongue to 0.1mM CuCl2 or ZnCl2. No significant difference in the amount ofinhibition by either salt was found among sugars. The concentration-responsecurve for sucrose was shifted towards the right along the abscissaby treating the tongue with CuCl2 or ZnCl2 at 0.1 mM. Reciprocalplots of the concentration-response relationship yielded straightlines, which intersected at a point along the ordinate. Theresults indicate that binding of surcrose as well as other sugarsto sweet receptor molecules is competitively inhibited by Cu2+or Zn2+. Responses to amino acids (Gly, L-Ala, L-Ser, L-Pro,L-Val and D-Trp) were either slightly or scarcely inhibitedby 0.1 mM CuCl2 or ZnCl2. Reciprocal plots of the concentration-responserelationship for Gly before and after adaptation of the tongueto either metal salt failed to yield straight lines. It is proposedthat amino acids would bind to a small proportion of sweet receptormolecules and, in addition, stimulate other receptor mechanismsresponsible for initiating impulses in fibers responsive totaste stimuli other than sucrose. |