DIFFERENCES IN CA2-TYPE GLUTAMATE-RECEPTOR CHANNELS IN NEOCORTICAL NEURONS CAUSED BY DIFFERENTIAL GLUR-B SUBUNIT EXPRESSION( PERMEABILITY OF AMPA)

Fast excitatory synaptic transmission in the CNS is mediated by AMPA-t ype glutamate receptor (GluR) channels. Heterologous expression sugges ted that the Ca2+ permeability of these receptors critically depends o n the subunit composition. Using patch-clamp techniques in brain slice s, we found that the Ca2+ permeability of native AMPA-type GluRs was m arkedly higher in nonpyramidal (P-Ca/P-K approximate to 0.63) than in pyramidal (P-Ca/P-K approximate to 0.05) neurons of rat neocortex. Ana lysis of mRNA in single cells indicated that the relative abundance of GluR-B-specific mRNA was significantly lower in nonpyramidal (GluR-B/ GluR-non-B approximate to 0.3) than in pyramidal (GlUR-B/GluR-non-B a pproximate to 3) cells. This suggests that differences in relative abu ndance of GluR-B-specific mRNA generate functional diversity of AMPA-t ype GluRs in neurons with respect to Ca2+ permeability.