Inwardly rectifying and Ca2+-permeable AMPA-type glutamate receptor channels in rat neocortical neurons.
Inwardly rectifying and Ca2+-permeable AMPA-type glutamate receptor channels in rat neocortical neurons. J. Neurophysiol. 78: 2592-2605, 1997. Current-voltage (I-V) relations and Ca2+ permeability of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)type glutamate receptor channels were investigated in neurons of rat neocortex by using the whole cell patch-clamp technique in brain slices. To activate AMPA receptor channels, kainate was used as a nondesensitizing agonist. A patch pipette was filled with solution containing 100 mu M spermine to maintain the inward rectification of Ca2+-permeable AMPA receptor channels. Three types of responses to kainate were observed: type I response with outwardly rectifying I-V relation, type II response with I-V relation of marked inward rectification, and intermediate response with I-V relation of weaker inward rectification. Neurons with type I, type II and intermediate I-V relations were referred to as type I, type II, and intermediate neurons, respectively. Of a total of 223 recorded cells, 90 (40.4%) were type I, 129 (57.8%) intermediate, and 4 (1.8%) type II neurons. Properties of AMPA receptor channels were examined in the former two types of neurons. The value of PCa:PCs, the ratio of the permeability coefficients of Ca2+ and Cs+, was estimated from the reversal potentials of kainate responses in the outside-out patches bathed in Na+-free solution containing 100 mM Ca2+ according to the constant-field equation. They ranged from 0.05 to 0.10 (0.08 +/- 0. 02, mean +/- SD, n = 8) for type I neurons and from 0.14 to 1.29 (0. 60 +/- 0.37, n = 11) for the intermediate neurons. There was a close correlation between the inward rectification and the Ca2+ permeability in AMPA receptor channels in these neurons. Intermediate neurons stained with biocytin were nonpyramidal cells with ellipsoidal-shaped somata. Type I neurons had either triangular- or ellipsoidal-shaped somata. Excitatory postsynaptic currents (EPSCs) recorded in both type I and intermediate neurons had 6-cyano-7-nitroquinoxaline-2,3-dione-sensitive fast and -2-amino-5-phosphonovalerate-sensitiveslow components. The I-V relation of the fast component exhibited inward rectification in the intermediate neuron, whereas that in the type I neuron showed slight outward rectification. The fast component of EPSCs in the intermediate neuron was suppressed more prominently (to 56 +/- 15% of the control, n = 12) than that in the type I neuron (to 78 +/- 6% of the control, n = 6) by bath application of 1 mM spermine. These results indicate that inwardly rectifying and Ca2+-permeable AMPA receptor channels are expressed in a population of neurons of rat neocortex and are involved in excitatory synaptic transmission.
Itazawa
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Department of Physiology, Gunma University School of Medicine, 3-39-22 Showa-machi, Maebashi, Gunma 371.
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Ozawa
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D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D000818:Animals; D001640:Bicuculline / Q000031:analogs & derivatives / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D004553:Electric Conductivity; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D007608:Kainic Acid / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009412:Nerve Fibers / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D009778:Occipital Lobe / Q000502:physiology*; D018408:Patch-Clamp Techniques; D051381:Rats; D018091:Receptors, AMPA / Q000502:physiology*; D011963:Receptors, GABA-A / Q000502:physiology; D013096:Spermine / Q000494:pharmacology; D013569:Synapses / Q000187:drug effects / Q000502:physiology; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid / Q000494:pharmacology*
D015220:Calcium Channels; D018091:Receptors, AMPA; D011963:Receptors, GABA-A; D013096:Spermine; C036615:bicuculline methobromide; D015763:2-Amino-5-phosphonovalerate; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; D007608:Kainic Acid; D002118:Calcium; D001640:Bicuculline