Taste responses to electrolytes in the frog glossopharyngeal nerve: enhancement by Ni2+ ions.
In studies of whole-nerve recordings from the frog glossopharyngeal nerve, Kashiwagura et al. reported that Ni2+ enhances responses to MgCl2 and NaCl and that such enhanced responses are suppressed by Ca2+. In the present study, it was found that the responses to electrolytes of single water fibers of the frog glossopharyngeal nerve are enhanced by Ni2+. Ni2+ enhances the responses to MgCl2, NaCl, and CaCl2. The enhancement of the response to CaCl2 suggests that inhibition of the enhanced response by Ca2+ is not caused by the relationship between Ca2+ and Ni2+ ions on the receptor membrane. Kitada reported that, in the absence of Ni2+, Ca2+ competitively inhibits the responses to Na+ and Mg2+; and Kitada and Shimada reported that the response to Ca2+ is competitively inhibited by Na+ and Mg2+. The possibility is discussed that inhibition of the enhanced response by Ca2+ is due to competition between Ca2+ and Na+ and between Ca2+ and Mg2+ for multiple specific receptor sites.