Abstract
1. Effects of pH on chorda tympani nerve responses to NaCl, KCl, sucrose and quinine of varying concentration and of the optimum temperature were investigated in rats.
2. Magnitudes of responses to NaCl in concentrations of 0.1M or lower were decreased linearly with lowering of pH of test solutions below 4.0, whereas those for 0.3M and 1M NaCl were independent of pH at 30°C. Depression of responses to NaCl by low pH were greater at 10°C than at 30°C. Magnitudes of responses to 0.01M, 0.3M and 1M KCl were increased as pH of test solutions was decreased below 4.0, but those of responses to 0.03M and 0.1M were independent of pH. pH dependency of the response to KCl was in marked contrast with that of the response to NaCl.
3. Magnitudes of responses to sucrose of varying concentrations were almost independent of pH, but slight decrease in the response magnitude was seen below pH 4.0.
4. Magnitudes of responses to quinine of varying concentrations were monotonously increased as pH of test solutions was decreased from 4.5 to 3.0.
5. Km or Michaelis constant of taste reaction was obtained from Beidler's taste equation and pH dependency of Km was examined. Thus, depression of responses to NaCl was attributed to the ionization of the receptor for NaCl, whereas facilitation of the responses to quinine was ascribed to that of the quinine receptor-quinine complex.
