Abstract: | Single fibers of the frog glossopharyngeal nerve respond toMgCl2 at concentrations exceeding 10 mM. NiCl2 at 1 mM enhancedthe Mg2+ response. CaCl2 at 0.52 mM induced an inhibitionof the Ni2+-enhanced response to Mg2+ ions. A quantitative explanationfor these results is provided by the hypothesis that Ni2+ ionssecondarily affect a magnesium receptor (designated X*Mg) thatis responsible for the Mg2+ response and that Ca2+ ions inhibitthe Ni2+-enhanced response to Mg2+ ions by competing with Mg2+ions for X*Mg. Double-reciprocal plots of the experimental dataindicate that Ni2+ ions do not affect the affinities of X*Mgfor both Mg2+ ions (agonist) and Ca2+ ions (competitive antagonist)appreciably, and that Ni2+ ions at 1 mM enhanced the maximalresponse to Mg2+ ions by 270%. It appears that a magnesium receptorinteracts with an Ni2+-binding element that is affected by Ni2+ions and, thus, Ni2+ ions can induce an enhancement of the Mg2+response. Chem. Senses 22: 613622,1997. |