Regional distribution and ionic requirement of Cl-/Ca2+-activated and Cl-/Ca2+-independent glutamate receptors in rat brain.

Recent studies have shown that Cl- and Ca2+ ions increase [3H]glutamate binding to rat forebrain synaptic plasma membranes by expressing a new class of glutamate receptors. We examined the regional distribution of these two classes of glutamate binding sites and further characterized their ionic requirements. Significant differences in both Cl-/Ca2+-independent (basal) and Cl-/Ca2+-activated receptors, as well as the ratios of these two receptor classes were observed among different areas of the CNS. Cl- and Ca2+ appeared to act synergistically, with Cl-ion an absolute requirement for Ca2+ stimulation, in expressing these additional binding sites. Ca2+ alone did not affect glutamate binding.