Abstract: | Several cations were examined for their ability to specifically affect one of the 3l-glutamate (l-Glu) binding sites in rat forebrain synaptic plasma membranes (i.e. Na+-dependent, Cl−-dependent and Cl−-independent). Na+-dependent binding was potently inhibited by K+ and NH4+ ions. Other monovalent cations testedd (Cs+, Li+, triethylammonium) had no effect on this binding site. Polyvalent cations (Co2+, Ni2+, Cu2+, Zn2+, Cd2+ and Cr3+) also had little effect on the Na+-dependentl-Glu binding site. Cl−-dependentl-Glu binding was potently inhibited by Na+ ions but was not affected by other monovalent ions. All of the divalent cations were potent inhibitors of both Cl−-dependent and -independent binding. The results show that these binding sites ofl-Glu can be distinguished by their response to cations and suggest possible novel modes of regulation in vivo. |