title: Evidence for Ca(2+)-permeable AMPA receptors in the olfactory bulb.
abstract: alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors (AMPARs), a subtype of glutamate receptor, contribute to olfactory processing in the olfactory bulb (OB). These ion channels consist of various combinations of the subunits GluR1-GluR4, which bestow certain properties. For example, AMPARs that lack GluR2 are highly permeable to Ca(2+) and generate inwardly rectifying currents. Because increased intracellular Ca(2+) could trigger a host of Ca(2+)-dependent odor-encoding processes, we used whole cell recording as well as histological and immunocytochemical (ICC) techniques to investigate whether AMPARs on rat OB neurons flux Ca(2+). Application of 1-naphthylacetyl spermine (NAS), a selective antagonist of Ca(2+)-permeable AMPARs (CP-AMPARs), inhibited AMPAR-mediated currents in subsets of interneurons and principal cells in cultures and slices. The addition of spermine to the electrode yielded inwardly rectifying current-voltage plots in some cells. In OB slices, olfactory nerve stimulation elicited excitatory responses in juxtaglomerular and mitral cells. Bath application of NAS with d,l-2-amino-5-phosphonovaleric acid (AP5) to isolate AMPARs suppressed the amplitudes of these synaptic responses compared with responses obtained using AP5 alone. Co(2+) staining, which involves the kainate-stimulated influx of Co(2+) through CP-AMPARs, produced diverse patterns of labeling in cultures and slices as did ICC techniques used with a GluR2-selective antibody. These results suggest that subsets of OB neurons express CP-AMPARs, including functional CP-AMPARs at synapses. Ca(2+) entry into cells via these receptors could influence odor encoding by modulating K(+) channels, N-methyl-d-aspartate receptors, and Ca(2+)-binding proteins, or it could facilitate synaptic vesicle fusion.
authors.affiliation: Department of Biological Science, Florida State University, Tallahassee, FL 32306-4340, USA.
authors.forename: L J
authors.initials: LJ
authors.lastname: Blakemore
authors.forename: M
authors.initials: M
authors.lastname: Resasco
authors.forename: M A
authors.initials: MA
authors.lastname: Mercado
authors.forename: P Q
authors.initials: PQ
authors.lastname: Trombley
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D005786:Gene Expression Regulation; D008564:Membrane Potentials; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D009830:Olfactory Bulb / Q000166:cytology / Q000378:metabolism*; D010539:Permeability; D051381:Rats; D017207:Rats, Sprague-Dawley; D018091:Receptors, AMPA / Q000235:genetics / Q000378:metabolism*; D013569:Synapses / Q000378:metabolism; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid / Q000378:metabolism
chemical_list: D018091:Receptors, AMPA; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; D002118:Calcium