Inwardly Rectifying and Ca-Permeable AMPA-Type Glutamate Receptor Channels in Rat Neocortical Neurons

Itazawa, Shun-Ichi, Tadashi Isa, and Seiji Ozawa. Inwardly taken from a set of four proteins; GluR1 (GluR-A), GluR2 rectifying and Ca-permeable AMPA-type glutamate receptor (GluR-B), GluR3 (GluR-C), and GluR4 (GluR-D). Exchannels in rat neocortical neurons. J. Neurophysiol. 78: 2592– pression studies have shown that functional properties of 2605, 1997. Current-voltage (I-V ) relations and Ca permeability of AMPA receptor channels depend on their subunit composia-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)tion: receptors possessing the GluR2 subunit exhibit either type glutamate receptor channels were investigated in neurons of a linear or outwardly rectifying I-V relation and little Ca rat neocortex by using the whole cell patch-clamp technique in permeability, whereas those lacking GluR2 show strong inbrain slices. To activate AMPA receptor channels, kainate was ward rectification and high Ca permeability (Burnashev used as a nondesensitizing agonist. A patch pipette was filled with solution containing 100 mM spermine to maintain the inward rectiet al. 1992; Hollmann and Heinemann 1994; Hume et al. fication of Ca-permeable AMPA receptor channels. Three types 1991; Seeburg 1993). of responses to kainate were observed: type I response with outIt was found that AMPA receptor channels exhibited wardly rectifying I-V relation, type II response with I-V relation marked inward rectification and high Ca permeability in of marked inward rectification, and intermediate response with Ia population of cultured rat hippocampal neurons (type II V relation of weaker inward rectification. Neurons with type I, type neurons) , whereas they exhibited an outwardly rectifying II and intermediate I-V relations were referred to as type I, type current-voltage (I-V ) relation and little Ca permeability II, and intermediate neurons, respectively. Of a total of 223 rein the majority of neurons (type I neurons) (Iino et al. 1990; corded cells, 90 (40.4%) were type I, 129 (57.8%) intermediate, Ozawa and Iino 1993; Ozawa et al. 1991b). Using a patchand 4 (1.8%) type II neurons. Properties of AMPA receptor chan-