Chem. Senses 27: 57-65,
2002
© Oxford University Press 2002
Electrophysiological Studies of Salty Taste Modification by Organic Acids in the Labellar Taste Cell of the Blowfly
1 Department of Life Science, Graduate School of Science and Technology, Kobe University, Kobe 657-8501, Japan 2 Department of Human Environment, Faculty of Human Development, Kobe University, Kobe 657-8501, Japan
Correspondence to be sent to: Naoko Kataoka-Shirasugi, Department of Human Environment, Faculty of Human Development, Kobe University, Kobe 657-8501, Japan. e-mail: naoshika{at}main.h.kobe-u.ac.jp
Using the labellar salt receptor cells of the blowfly, Phormia regina, we electrophysiologically showed that the response to NaCl and KCl aqueous solutions was enhanced and depressed by acetic, succinic and citric acids. The organic acid concentrations at which the most enhanced salt response (MESR) was obtained were found to be different: 0.05-1 mM citric acid, 0.5-2 mM succinic acid and 5-50 mM acetic acid. Moreover, the degree of the salt response was not always dependent on the pH values of the stimulating solutions. The salt response was also enhanced by HCl (pH 3.5-3.0) only when the NaCl concentration was greater than the threshold, indicating that the salty taste would be enhanced by the comparatively lower concentrations of hydrogen ions. Another explanation for the enhancement is that the salty taste may also be enhanced by undissociated molecules of the organic acids, because the MESRs were obtained at the pH values lower than the pKa1 or pKa2 values of these organic acids. On the other hand, the salty taste could be depressed by both the lower pH range (pH 2.5-2.0) and the dissociated organic anions from organic acid molecules with at least two carboxyl groups.