Glial cells in the mouse hippocampus express AMPA receptors with an intermediate Ca2+ permeability.
Recently, we could demonstrate the 'complex' glial cells in mouse hippocampal slices express glutamate receptor changes of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate subtypes. In the present study, we further characterized this glial receptor. Since voltage-clamp control is imperfect and diffusion barriers hinders the quantitative analysis of the receptor currents in situ, the patch-clamp technique was applied to glial cells acutely isolated from the mouse hippocampal CA1 stratum radiatum subregion. A concentration-clamp technique was used which enabled very fast exchange of the extracellular solutions. Thus, it was possible to characterize the transient receptor currents with high time resolution. Application of L-glutamate, AMPA and L-homocysteate induced rapidly activating and fast desensitizing receptor currents in the suspended glial cells. In contrast, kainate induced non-desensitizing currents. The corresponding dose-response curve revealed a half-maximum of current activation at 350 microM. The current/voltage relationship of the kainate-evoked response was linear with a reversal potential at approximately 9 mV. Analysis of the reversal potential in solutions containing high concentrations of CaCl2 confirmed earlier in situ data by demonstrating significant Ca2+ permeability of the glial glutamate receptor channels in the hippocampus. The kainate-induced receptor currents were markedly increased by cyclothiazide, a substance which selectively potentiates glutamate receptors of the AMPA subtype. We conclude that glial cells of the juvenile hippocampus mainly express heteromeric high-affinity AMPA receptors. Most probably, the receptor channels are assembled from the low Ca(2+)-permeable glutamate receptor-2 subunit together with Ca(2+)-permeable AMPA-preferring subunits.
Institute of Physiology, Friedrich-Schiller University, Jena, Germany.
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D000818:Animals; D001581:Benzothiadiazines / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002463:Cell Membrane Permeability / Q000502:physiology; D004058:Diffusion; D004232:Diuretics; D004566:Electrodes; D005260:Female; D006624:Hippocampus / Q000166:cytology / Q000378:metabolism*; D006710:Homocysteine / Q000378:metabolism; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D007700:Kinetics; D051379:Mice; D009457:Neuroglia / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D018091:Receptors, AMPA / Q000096:biosynthesis*; D018092:Kainic Acid Receptors / Q000187:drug effects; D049993:Sodium Chloride Symporter Inhibitors / Q000494:pharmacology
D001581:Benzothiadiazines; D002118:Calcium; D004232:Diuretics; D006710:Homocysteine; D018091:Receptors, AMPA; D018092:Kainic Acid Receptors; D049993:Sodium Chloride Symporter Inhibitors; C004639:cyclothiazide