A high GluR1 : GluR2 expression ratio is correlated with expression of Ca2+-binding proteins in rat forebrain neurons.
alpha-Amino-3-hydroxy-5-methyl-4-isoxazle propionic acid (AMPA) receptors are ubiquitously expressed; however, their subtypes and abundance vary from region to region. We classified the neurons in various forebrain regions (hippocampus, striatum, amygdala, piriform cortex and somatosensory cortex) into six types: [R1+/R2+], [R1-/R2+], [R1+/R2-], [R1-/R2-], [R1++/R2+] and [R1++/R2-], and analysed the expression of Ca2+-binding proteins, such as parvalbumin and calbindin-D28k, using a triple-staining method. The neurons showing a high GluR1 : GluR2 expression ratio, [R1+/R2-], [R1++/R2+] and [R1++/R2-] neurons, comprised 13-30% of the total neuronal population. In addition, the expression of Ca2+-binding proteins was mainly observed in these three types of neurons. The results suggest that Ca2+-binding protein-positive neurons express Ca2+-permeable AMPA receptors, because the Ca2+-permeability of AMPA receptors is enhanced by the relative scarcity of the GluR2 subunit. To directly test the possibility that Ca2+-binding protein-positive neurons express Ca2+-permeable AMPA receptors, we performed Ca2+-imaging experiments in cultured cortical neurons. Ca2+ influx through AMPA receptors was measured selectively by addition of AMPA together with cyclothiazide in the presence of blockers of other Ca2+ influx routes. More than half of the calbindin-D28k-positive neurons showed a large increase in the intracellular Ca2+ concentration ([Ca2+]i), whilst most of the calbindin-D28k-undetectable neurons exhibited only a slight rise in [Ca2+]i after AMPA addition. These results suggest that the expression of calbindin-D28k is related to the expression of Ca2+-permeable AMPA receptors.
Kondo
M
M
Department of Neurobiology, Tokyo Metropolitan Institute for Neuroscience, 2-6 Musashidai, Fuchu 183-8526, Japan. mkondo@tmin.ac.jp
Okabe
S
S
Sumino
R
R
Okado
H
H
D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology; D001581:Benzothiadiazines / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D064092:Calbindin 1; D064026:Calbindins; D002118:Calcium / Q000032:analysis / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002478:Cells, Cultured; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D015870:Gene Expression / Q000502:physiology; D017403:In Situ Hybridization; D009474:Neurons / Q000145:classification / Q000166:cytology / Q000378:metabolism*; D010320:Parvalbumins / Q000032:analysis / Q000235:genetics; D016548:Prosencephalon / Q000737:chemistry / Q000166:cytology / Q000502:physiology*; D011810:Quinoxalines / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D018091:Receptors, AMPA / Q000032:analysis / Q000235:genetics*; D064030:S100 Calcium Binding Protein G / Q000032:analysis / Q000235:genetics*; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid / Q000494:pharmacology
D000959:Antihypertensive Agents; D001581:Benzothiadiazines; D064092:Calbindin 1; D064026:Calbindins; D002118:Calcium; D002121:Calcium Channel Blockers; D018690:Excitatory Amino Acid Agonists; D018691:Excitatory Amino Acid Antagonists; D010320:Parvalbumins; D011810:Quinoxalines; D012333:RNA, Messenger; D018091:Receptors, AMPA; D064030:S100 Calcium Binding Protein G; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; C576500:Calb1 protein, rat; C062865:2,3-dioxo-6-nitro-7-sulfamoylbenzo(f)quinoxaline; C104722:glutamate receptor ionotropic, AMPA 2; C004639:cyclothiazide