Distribution of neurones expressing inwardly rectifying and Ca(2+)-permeable AMPA receptors in rat hippocampal slices.
1. Current-voltage (I-V) relationships and Ca2+ permeability of receptor channels activated by bath application of kainate, a non-desensitizing agonist of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, were examined in various types of neurones in hippocampal slices of 5- to 13-day-old rats by using the tight-seal patch clamp recording technique. 2. Three types of responses were observed: type I response with outwardly rectifying I-V relationship, type II response with I-V relationship of marked inward rectification, and intermediate response with I-V relationship of weaker inward rectification. Neurones with type I, type II and intermediate I-V relationships of kainate responses were referred to as type I, type II and intermediate neurones, respectively. 3. Permeability of Ca2+ ions was estimated by the reversal potential of kainate response in the outside-out patch in Na(+)-free extracellular solution containing 100 mM Ca2+. The reversal potentials were -44.4 +/- 14.0 mV (mean +/- S.D.) for type I (n = 7), +11.8 +/- 3.6 mV for type II (n = 5), and -8.7 +/- 7.4 mV for the intermediate neurones (n = 7). The values of PCa/PCs, the ratios of the permeability coefficients of Ca2+ and Cs+, estimated according to the constant-field equation were 0.08 for type I, 1.71 for type II, and 0.50 for the intermediate neurones. 4. Type II and intermediate responses were observed mainly in non-pyramidal neurones in various areas of the hippocampus, most frequently observed in the stratum molecular of the dentate gyrus and in the stratum radiatum and the stratum lacunosum-molecular of both the CA1 and CA3 regions. Both type II and intermediate neurones stained with biocytin had round- or ellipsoidal-shaped somata and issued divergent axonal projections to the surrounding structures. 5. Excitatory postsynaptic currents (EPSCs) recorded in type II neurones had 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX)-sensitive fast and D-2-amino-5-phosphonovalerate (APV)-sensitive slow components. The I-V relationship of the fast component showed a strong inward rectification, indicating that inwardly rectifying AMPA receptors are involved in excitatory synaptic transmission.
Isa
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Department of Physiology, School of Medicine, Gunma University, Japan.
Itazawa
S
S
Iino
M
M
Tsuzuki
K
K
Ozawa
S
S
D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D006624:Hippocampus / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D066298:In Vitro Techniques; D007608:Kainic Acid / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000378:metabolism* / Q000648:ultrastructure; D018408:Patch-Clamp Techniques; D051381:Rats; D018091:Receptors, AMPA / Q000378:metabolism*; D009435:Synaptic Transmission / Q000502:physiology; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid / Q000494:pharmacology
D018690:Excitatory Amino Acid Agonists; D018691:Excitatory Amino Acid Antagonists; D018091:Receptors, AMPA; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D015763:2-Amino-5-phosphonovalerate; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; D007608:Kainic Acid; D002118:Calcium