Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
Comparative Study
. 2008 Apr;27(7):1686-99.
doi: 10.1111/j.1460-9568.2008.06141.x. Epub 2008 Mar 25.

Unique clustering of A-type potassium channels on different cell types of the main olfactory bulb

Mihaly Kollo  1 , Noémi Holderith, Miklós Antal, Zoltan Nusser
Affiliations
Comparative Study

Unique clustering of A-type potassium channels on different cell types of the main olfactory bulb

Mihaly Kollo et al. Eur J Neurosci. 2008 Apr.

Abstract

Theoretical and functional studies predicted a highly non-uniform distribution of voltage-gated ion channels on the neuronal surface. This was confirmed by recent immunolocalization experiments for Na+, Ca2+, hyperpolarization activated mixed cation and K+ channels. These experiments also indicated that some K+ channels were clustered in synaptic or non-synaptic membrane specializations. Here we analysed the subcellular distribution of Kv4.2 and Kv4.3 subunits in the rat main olfactory bulb at high resolution to address whether clustering characterizes their distribution, and whether they are concentrated in synaptic or non-synaptic junctions. The cell surface distribution of the Kv4.2 and Kv4.3 subunits is highly non-uniform. Strong Kv4.2 subunit-immunopositive clusters were detected in intercellular junctions made by mitral, external tufted and granule cells (GCs). We also found Kv4.3 subunit-immunopositive clusters in periglomerular (PGC), deep short-axon and GCs. In the juxtaglomerular region some calretinin-immunopositive glial cells enwrap neighboring PGC somata in a cap-like manner. Kv4.3 subunit clusters are present in the cap membrane that directly contacts the PGC, but not the one that faces the neuropil. In membrane specializations established by members of the same cell type, K+ channels are enriched in both membranes, whereas specializations between different cell types contain a high density of channels asymmetrically. None of the K+ channel-rich junctions showed any of the ultrastructural features of known chemical synapses. Our study provides evidence for highly non-uniform subcellular distributions of A-type K+ channels and predicts their involvements in novel forms of intercellular communication in the olfactory pathway.

PubMed Disclaimer

Figures

Fig. 1
Fig. 1
Distribution of A-type potassium channel subunits Kv4.2 and Kv4.3 in the main olfactory bulb (MOB). (A) Identical labeling was obtained with two antibodies, raised against different parts of the Kv4.2 subunit, indicating that the observed immunosignal is due to specific antibody-Kv4.2 subunit interaction. (B) No labeling was observed in Kv4.2 knockout mouse with the rabbit anti-Kv4.2 antibody, further validating the specificity of the immunoreaction. The strongest immunoreaction is seen in the granule cell layer (GCL) and external plexiform layer (EPL). (C) The specificity of Kv4.3 immunolabeling was tested by performing triple labeling experiments with three different antibodies (rabbit (R): red, goat (G): green, mouse (M): blue). The identical labeling of the MOB indicates that all signals are the consequence of specific antibody-Kv4.3 subunit interaction. The glomerular layer (GL) shows the most intense labeling for the Kv4.3 subunit. Scale bar is 100 μm and applies to all panels.
Fig. 2
Fig. 2
Distribution of the Kv4.2 and Kv4.3 subunits in the granule cell layer. (A) Clustered Kv4.2 subunit immunolabeling is observed in a subpopulation of granule cells (arrowheads). (B) A large deep short axon cell (*) is strongly labeled for the Kv4.3 subunit. A small number of granule cells also shows clustered labeling (arrowhead). (C) Double immunofluorescent labeling for the Kv4.2 and Kv4.3 subunits. Some granule cells express clusters of either the Kv4.2 (green arrowheads) or the Kv4.3 subunits (red arrowheads), whereas in some other granule cells Kv4.2 and Kv4.3 subunits colocalize (yellow arrowheads). (D) Strongly Kv4.3 subunit immunolabeled clusters (red arrowheads) are found in a deep short axon cell (*) close to strongly Kv4.2 subunit immunopositive granule cells (green arrowheads). Scale bars: 30 μm (A and B); 10 μm (C and D).
Fig. 3
Fig. 3
Electron microscopic immunogold localization reveals the subcellular distribution of the Kv4.2 and Kv4.3 subunits in the granule cell layer. (A) Immunogold particles for Kv4.2 subunit are clustered in membrane specializations (filled arrowheads) between granule cell somata (GCs) and dendrites (GCd). A part of the granule cell plasma membrane, which is not in direct contact with other granule cell processes (open arrowheads), contains a low density of labeling. (B) In such K+ channel-rich specializations, both apposing granule cell membranes are strongly labeled for the Kv4.2 subunit. (C) Kv4.2 subunit immunopositive junctions (filled arrowheads) are frequently observed between granule cell dendrites (GCd) in the GCL. Open arrowhead points to a synaptic junction. (D) Clustered immunolabeling for Kv4.2 subunit (filled arrowheads) is occasionally found around symmetrical synapses (e.g. open arrowhead) on a granule cell dendrite. (E and F) Clusters of gold particles for the Kv4.3 subunit (filled arrowheads) are observed in a deep short-axon cell (dSAC) contacting a granule cell soma (GCs). The high density of labeling is absent from other parts of the plasma membrane (open arrowheads in E). (F) Light microscopic image of the cells shown in E taken before EM sectioning. (G) A higher magnification image of the Kv4.3 subunit-rich specializations (filled arrowheads) between a dSAC and a granule cell soma (GCs). (H) Rare Kv4.3 subunit immunopositive junctions (filled arrowheads) between granule cell somata (GCs) are shown. Note that both apposing parts of the membrane specializations are labeled. Scale bars: 1.5 μm (A); 0.1 μm (B); 0.3 μm (C-E, G, H); 2 μm (E); 10 μm (F).
Fig. 4
Fig. 4
Distribution of the Kv4.2 and Kv4.3 subunits in the mitral cell and external plexiform layer. (A) Strongly Kv4.2 subunit immunolabeled dendrites (open arrowheads) dominate the homogeneous labeling of the neuropil of the external plexiform layer. A few immunopositive cell bodies are also observed (e.g. filled arrowhead) in the EPL. (B) A few Kv4.3 subunit immunopositive cell bodies (e.g. open arrowheads) stand out from the homogeneous labeling of the neuropil. (C) Double immunofluorescent labeling for the Kv4.2 and Kv4.3 subunits demonstrate their colocalization in clusters on mitral cells somata (yellow open arrowheads). (D and E) Distal parts of mitral cell apical dendrites are outlined by Kv4.2 (D) and Kv4.3 (E) subunit labeling. (F) Parvalbumin (red) immunonegative cell bodies are decorated by Kv4.2 subunit immunopositive clusters (green open arrowheads). (G) A parvalbumin immunopositive cell (green open arrowhead) of the EPL is decorated by strong Kv4.3 subunit positive clusters. Scale bars: 50 μm (A and B); 10 μm (C-G).
Fig. 5
Fig. 5
Electron microscopic immunogold localization of the Kv4.2 subunit in the mitral cell and external plexiform layers. (A) Clusters of immunogold particles for the Kv4.2 subunits are observed in membrane specializations (filled arrowheads) between two mitral cell dendrites (MCd). Note that gold particles are present in the membrane of both cells. A low intensity labeling was also found in MC lateral dendrites (open arrowheads). (B) Immunogold labeling is present in the glial sheet wrapping mitral cell apical dendrites (MCd). (C and D) A granule cell dendrite (GCd in C) and a gemmule (GCg in D) form strongly immunopositive membrane specializations with mitral cell dendrites (MCd). At these junctions, gold particles (filled arrowheads) are only found in the plasma membrane of the mitral cells. A lower density of labeling is also observed in these cells outside the specializations (open arrowheads). (E) Kv4.2 subunit immunopositive specializations are shown between granule cell dendrites (GCd) ascending into the EPL (filled arrowheads). (F) Kv4.2 immunopositive specializations (filled arrowheads) are observed in the soma of a short axon cell (SAC). Scale bars: 0.3 μm.
Fig. 6
Fig. 6
Distribution of the Kv4.2 and Kv4.3 subunits in the glomerular layer. (A) In addition to the weak neuropil labeling of the glomeruli, some juxtaglomerular cells (open arrowheads) are strongly Kv4.2 subunit immunopositive. (B) The uneven distribution of Kv4.2 subunit immunolabeling is revealed at higher magnifications. Small clusters are arranged either in disk-like (open arrowhead) or string-like (filled arrowhead) shapes. (C and D) Kv4.2 (red) subunit immunopositive cells are VGLUT2 (green) expressing external tufted cells. (E) Reticular-like labeling of the glomerular neuropil is found for the Kv4.3 subunit, in addition to a small number of immunopositive periglomerular cells (open arrowheads). (F) Double Kv4.3 subunit (green) and calretinin (CR: red) immunolabeling reveals that the intense Kv4.3 subunit clusters are often present on CR+ cells. (G) A strongly Kv4.3 subunit immunopositive process of a CR+ cell (open arrowheads) envelops another juxtaglomerular cell (*, note the nucleus on the DIC image). epifluorescent images (A and C-F); ‘extended focal image’ projection of 18 optical sections taken at 0.38 μm (B); single confocal sections (G); Scale bars: 25 μm (A and E); 20 μm (F); 10 μm (B, C, D and G).
Fig. 7
Fig. 7
Electron microscopic immunogold localization of the Kv4.2 and Kv4.3 subunits in the glomerular layer. (A) Clusters of immunogold particles for the Kv4.2 subunit (filled arrowheads) are shown along the somatic plasma membrane of an external tufted cell (ETC) that is in direct contact with a periglomerular cell (PGC). Part of the plasma membrane that faces the neuropil (open arrowheads) is not labeled. (B) A high magnification view of an immunopositive cluster (filled arrowheads) on an ETC soma reveals that the gold particles are enriched in a membrane specialization. (C and D) Glial processes wrapping mitral/tufted cell dendrites (MCd) are labeled for the Kv4.2 subunit (filled arrowheads). A low density of labeling (open arrowheads) is found on the plasma membrane of mitral/tufted cell dendrites (MCd), which form synapses in the glomerulus (arrows). (E) Strong immunogold labeling for Kv4.3 subunit is seen in a process enwrapping the soma of a periglomerular cell (PGC). The density of the gold particles is much higher along the membrane (filled arrowheads) that touches the PGC soma than that contacting the surrounding neuropil (open arrowheads). (F) A Kv4.3 subunit immunopositive process forms a thin sheet around a PGC. (G and H) Kv4.3 subunit positive clusters are observed on dendrites (d) in the glomerulus, which receive asymmetrical synapses (filled arrowhead) from other dendrites. Scale bars: 0.5 μm (A, C, E, G and H); 0.3 μm (B, D and F).
Fig. 8
Fig. 8
Three-dimensional reconstruction of Kv4.2 and Kv4.3 subunit immunopositive cells and schematic representation of the main cellular elements, containing K+ channel-rich junctions. (A) 3D reconstruction of a periglomerular cell soma (blue) enwrapped by a cap-like process (yellow). (B) Distribution of the Kv4.3 subunit in the plasma membrane of the process (transparent yellow). The density of the immunogold particles on the inner membrane of the cap, contacting the cell body (contact), is much higher than that on the outer membrane (non-contact). Gold particles labeling the Kv4.3 subunit are represented as black dots. An electron micrograph from the series used for the reconstruction is shown. Scale bar: 1 μm. (C) 3D reconstruction of two granule cell somata contacting each other. (D) Distribution of the Kv4.2 subunit in the plasma membrane of one of the granule cells (yellow cell). The labeling is more intense where the cell is in contact (contact) with the other granule cell (blue cell) compared to the rest of the somatic plasma membrane (non-contact). The length of each edge of the cubes: 1 μm. (E) Schematic representation of the clustered subcellular distribution of the Kv4.2 subunit in the MOB. Clusters of the subunit were found on both sides of junctions between: somata of granule cells (green, 1), mitral cells (yellow, 2) and dendrites of mitral cells (3). Asymmetrical enrichment of the Kv4.2 subunit was observed in: mitral cells contacting granule cell dendrites (4), external tufted cells (yellow) contacting periglomerular cell (blue) dendrites (5) and somata (6). The glial sheath surrounding the distal part of the mitral cell apical dendrites also showed clustered immunolabeling (7). (F) Schematic representation of the clustered subcellular distribution of the Kv4.3 subunit. Punctuate labeling of the subunit was found in both sides of conjunctions between the somata of a small number of granule cells (1). Clusters of the subunit were observed in: a subpopulation of deep short-axon cells (light blue) contacting granule cell somata (2), processes of a gliaform juxtaglomerular cell forming perisomatic caps around periglomerular cells (3), and in periglomerular cell dendrites contacting other dendrites in the glomeruli (4).
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

References

    1. Alonso G, Widmer H. Clustering of KV4.2 potassium channels in postsynaptic membrane of rat supraoptic neurons: an ultrastructural study. Neuroscience. 1997;77:617–621. - PubMed
    1. An WF, Bowlby MR, Betty M, Cao J, Ling HP, Mendoza G, Hinson JW, Mattsson KI, Strassle BW, Trimmer JS, Rhodes KJ. Modulation of A-type potassium channels by a family of calcium sensors. Nature. 2000;403:553–556. - PubMed
    1. Antal M, Eyre M, Finklea B, Nusser Z. External tufted cells in the main olfactory bulb form two distinct subpopulations. Eur J Neurosci. 2006;24:1124–1136. - PMC - PubMed
    1. Birnbaum SG, Varga AW, Yuan LL, Anderson AE, Sweatt JD, Schrader LA. Structure and function of Kv4-family transient potassium channels. Physiol Rev. 2004;84:803–833. - PubMed
    1. Boiko T, Rasband MN, Levinson SR, Caldwell JH, Mandel G, Trimmer JS, Matthews G. Compact myelin dictates the differential targeting of two sodium channel isoforms in the same axon. Neuron. 2001;30:91–104. - PubMed

Publication types

Substances