A quantitative study of the enhancing effect of nickel ions on the taste response to sodium ions of single fibers of the frog glossopharyngeal nerve: Competitive inhibition by calcium ions of the nickel-enhanced response to sodium ions

Yasuyuki Kitada, Yoshihiro Mitoh

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Abstract

Single water fibers of the frog glossopharyngeal nerve respond to relatively high concentrations of NaCl (>80 mM). NiCl2 at 1 mM enhanced the Na+ response and reduced the threshold concentration for NaCl to 20 mM. CaCl2 at 0.5-1 mM induced an inhibition of the Ni2+-enhanced response to Na+ ions. A quantitative explanations for these results is provided by the hypothesis that Ni2+ ions secondarily affect a sodium receptor or channel (designated XNa*) that is responsible for the Na+ response and that Ca2+ ions inhibit the Ni2+-enhanced response to Na+ ions by competing with Na+ ions for XNa*. Double-reciprocal plots of the experimental data indicate that the affinity of XNa* for both Na+ ions (agonist) and Ca2+ ions (competitive antagonist) in the presence of 1 mM NiCl2 was five times higher than the previously reported values obtained in the absence of NiCl2 (Kitada, 1991). Ni2+ ions at 1 mM enhanced the maximal response to Na+ ions by 190%. It appears that a sodium receptor (or channel) interacts with a Ni2+-binding element that is affected by Ni2+ ions and, thus, Ni2+ ions can induce both an increase in the affinity of the sodium receptor for the respective cations and an enhancement of the Na+ response.

Original languageEnglish
Pages (from-to)65-73
Number of pages9
JournalChemical Senses
Volume21
Issue number1
DOIs
Publication statusPublished - Jan 1 1996

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ASJC Scopus subject areas

  • Physiology
  • Sensory Systems
  • Physiology (medical)
  • Behavioral Neuroscience

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