Focal Aggregation of Voltage-Gated, Kv2.1 Subunit-Containing, Potassium Channels at Synaptic Sites in Rat Spinal Motoneurones

Delayed rectifier K+ currents are involved in the control of alpha-motoneurone excitability, but the precise spatial distribution and organization of the membrane ion channels that contribute to these currents have not been defined. Voltage-activated Kv2.1 channels have properties commensurate with a contribution to delayed rectifier currents and are expressed in neurones throughout the mammalian central nervous system. A specific antibody against Kv2.1 channel subunits was used to determine the surface distribution and clustering of Kv2.1 subunit-containing channels in the cell membrane of alpha-motoneurones and other spinal cord neurones. In alpha-motoneurones, Kv2.1 immunoreactivity (-IR) was abundant in the surface membrane of the soma and large proximal dendrites, and was present also in smaller diameter distal dendrites. Plasma membrane-associated Kv2.1-IR in alpha-motoneurones was distributed in a mosaic of small irregularly shaped, and large disc-like, clusters. However, only small to medium clusters of Kv2.1-IR were observed in spinal interneurones and projection neurones, and some interneurones, including Renshaw cells, lacked demonstrable Kv2.1-IR. In alpha-motoneurones, dual immunostaining procedures revealed that the prominent disc-like domains of Kv2.1-IR are invariably apposed to presynaptic cholinergic C-terminals. Further, Kv2.1-IR colocalizes with immunoreactivity against postsynaptic muscarinic (m2) receptors at these locations. Ultrastructural examination confirmed the postsynaptic localization of Kv2.1-IR at C-terminal synapses, and revealed clusters of Kv2.1-IR at a majority of S-type, presumed excitatory, synapses. Kv2.1-IR in alpha-motoneurones is not directly associated with presumed inhibitory (F-type) synapses, nor is it present in presynaptic structures apposed to the motoneurone. Occasionally, small patches of extrasynaptic Kv2.1-IR labelling were observed in surface membrane apposed by glial processes. Voltage-gated potassium channels responsible for the delayed rectifier current, including Kv2.1, are usually assigned roles in the repolarization of the action potential. However, the strategic localization of Kv2.1 subunit-containing channels at specific postsynaptic sites suggests that this family of voltage-activated K+ channels may have additional roles and/or regulatory components

Focal Aggregation of Voltage-Gated, Kv2.1 Subunit-Containing, Potassium Channels at Synaptic Sites in Rat Spinal Motoneurones

Delayed rectifier K+ currents are involved in the control of alpha-motoneurone excitability, but the precise spatial distribution and organization of the membrane ion channels that contribute to these currents have not been defined. Voltage-activated Kv2.1 channels have properties commensurate with a contribution to delayed rectifier currents and are expressed in neurones throughout the mammalian central nervous system. A specific antibody against Kv2.1 channel subunits was used to determine the surface distribution and clustering of Kv2.1 subunit-containing channels in the cell membrane of alpha-motoneurones and other spinal cord neurones. In alpha-motoneurones, Kv2.1 immunoreactivity (-IR) was abundant in the surface membrane of the soma and large proximal dendrites, and was present also in smaller diameter distal dendrites. Plasma membrane-associated Kv2.1-IR in alpha-motoneurones was distributed in a mosaic of small irregularly shaped, and large disc-like, clusters. However, only small to medium clusters of Kv2.1-IR were observed in spinal interneurones and projection neurones, and some interneurones, including Renshaw cells, lacked demonstrable Kv2.1-IR. In alpha-motoneurones, dual immunostaining procedures revealed that the prominent disc-like domains of Kv2.1-IR are invariably apposed to presynaptic cholinergic C-terminals. Further, Kv2.1-IR colocalizes with immunoreactivity against postsynaptic muscarinic (m2) receptors at these locations. Ultrastructural examination confirmed the postsynaptic localization of Kv2.1-IR at C-terminal synapses, and revealed clusters of Kv2.1-IR at a majority of S-type, presumed excitatory, synapses. Kv2.1-IR in alpha-motoneurones is not directly associated with presumed inhibitory (F-type) synapses, nor is it present in presynaptic structures apposed to the motoneurone. Occasionally, small patches of extrasynaptic Kv2.1-IR labelling were observed in surface membrane apposed by glial processes. Voltage-gated potassium channels responsible for the delayed rectifier current, including Kv2.1, are usually assigned roles in the repolarization of the action potential. However, the strategic localization of Kv2.1 subunit-containing channels at specific postsynaptic sites suggests that this family of voltage-activated K+ channels may have additional roles and/or regulatory components

Differential Distribution of Kv2.1 Channels in Spinal Neurons

Kv2.1 channel subunits are widely expressed in the mammalian CNS. These channels underlie delayed rectifier currents and likely have important roles in the regulation of dendritic excitability and synaptic currents. Previously, using specific antibodies, Kv2.1 channels were localized to high density plasma membrane clusters restricted to the soma and proximal dendrites of cortical and hippocampal neurons. The Kv2.1 clusters in these cells are associated with a variety of specialized membrane regions such as subsurface cisternae as well as surface membrane apposed to astrocytic processes and to some presumed inhibitory synapses. Here, we analyzed the cellular and subcellular distribution of Kv2.1 channels in a variety of defined classes of spinal cord neurons, including motoneurons (MNs), interneurons, and dorsal spinocerebellar tract (DSCT) cells. Use of a specific anti Kv2.1 mAb (Upstate) revealed very large patches of immunostaining localized to the soma and proximal dendrites of MNs. Interneurons in laminae III-VIII and X expressed smaller surface punctae. Notably, DSCT cells and Renshaw cells express less intense Kv2.1 labeling, in much smaller patches, suggesting that the membrane organization of Kv2.1 is cell-type specific. The localization of Kv2.1 in MNs was further explored by double labeling with Abs against a variety of neurotransmitters and receptors. At the light microscope level, almost all of the large Kv2.1 clusters in MNs were closely apposed by large nerve terminals labeled by Abs against the vesicular acetylcholine transporter and appeared to be colocalized with postsynaptic m2 muscarinic receptors. Kv2.1 channels thus appear to be localized at cholinergic C-terminal synapses, which are characterized by their prominent subsurface cisternae. The relationship of Kv2.1 with C-terminals was confirmed at the ultrastructural level

Differential Distribution of Kv2.1 Channels in Spinal Neurons

Kv2.1 channel subunits are widely expressed in the mammalian CNS. These channels underlie delayed rectifier currents and likely have important roles in the regulation of dendritic excitability and synaptic currents. Previously, using specific antibodies, Kv2.1 channels were localized to high density plasma membrane clusters restricted to the soma and proximal dendrites of cortical and hippocampal neurons. The Kv2.1 clusters in these cells are associated with a variety of specialized membrane regions such as subsurface cisternae as well as surface membrane apposed to astrocytic processes and to some presumed inhibitory synapses. Here, we analyzed the cellular and subcellular distribution of Kv2.1 channels in a variety of defined classes of spinal cord neurons, including motoneurons (MNs), interneurons, and dorsal spinocerebellar tract (DSCT) cells. Use of a specific anti Kv2.1 mAb (Upstate) revealed very large patches of immunostaining localized to the soma and proximal dendrites of MNs. Interneurons in laminae III-VIII and X expressed smaller surface punctae. Notably, DSCT cells and Renshaw cells express less intense Kv2.1 labeling, in much smaller patches, suggesting that the membrane organization of Kv2.1 is cell-type specific. The localization of Kv2.1 in MNs was further explored by double labeling with Abs against a variety of neurotransmitters and receptors. At the light microscope level, almost all of the large Kv2.1 clusters in MNs were closely apposed by large nerve terminals labeled by Abs against the vesicular acetylcholine transporter and appeared to be colocalized with postsynaptic m2 muscarinic receptors. Kv2.1 channels thus appear to be localized at cholinergic C-terminal synapses, which are characterized by their prominent subsurface cisternae. The relationship of Kv2.1 with C-terminals was confirmed at the ultrastructural level

Differential Distribution of Kv2.1 Channels in Spinal Neurons

Kv2.1 channel subunits are widely expressed in the mammalian CNS. These channels underlie delayed rectifier currents and likely have important roles in the regulation of dendritic excitability and synaptic currents. Previously, using specific antibodies, Kv2.1 channels were localized to high density plasma membrane clusters restricted to the soma and proximal dendrites of cortical and hippocampal neurons. The Kv2.1 clusters in these cells are associated with a variety of specialized membrane regions such as subsurface cisternae as well as surface membrane apposed to astrocytic processes and to some presumed inhibitory synapses. Here, we analyzed the cellular and subcellular distribution of Kv2.1 channels in a variety of defined classes of spinal cord neurons, including motoneurons (MNs), interneurons, and dorsal spinocerebellar tract (DSCT) cells. Use of a specific anti Kv2.1 mAb (Upstate) revealed very large patches of immunostaining localized to the soma and proximal dendrites of MNs. Interneurons in laminae III-VIII and X expressed smaller surface punctae. Notably, DSCT cells and Renshaw cells express less intense Kv2.1 labeling, in much smaller patches, suggesting that the membrane organization of Kv2.1 is cell-type specific. The localization of Kv2.1 in MNs was further explored by double labeling with Abs against a variety of neurotransmitters and receptors. At the light microscope level, almost all of the large Kv2.1 clusters in MNs were closely apposed by large nerve terminals labeled by Abs against the vesicular acetylcholine transporter and appeared to be colocalized with postsynaptic m2 muscarinic receptors. Kv2.1 channels thus appear to be localized at cholinergic C-terminal synapses, which are characterized by their prominent subsurface cisternae. The relationship of Kv2.1 with C-terminals was confirmed at the ultrastructural level

Clustering of Kv2.1 Potassium Channels in Spinal Neurons

Kv2.1 channel subunits underlie delayed rectifier potassium currents that are expressed in neurons throughout the mammalian CNS. We used confocal and electron microscopy to analyze the subcellular localization of these channels in a variety of rat spinal cord neurons, including motoneurons (MNs), interneurons, and dorsal spinocerebellar tract (DSCT) cells, using a commercially available monoclonal antibody against Kv2.1 (Upstate). Kv2.1 immunoreactivity appeared as distinct surface membrane clusters in somatic and proximal dendritic regions. Clusters varied in size and complexity depending on neuron type, with the largest clusters seen on MNs. Quantitative analysis of Kv2.1 channel clusters (n=225 \u27en face\u27 clusters) on MNs revealed a bimodal size distribution including small

Clustering of Kv2.1 Potassium Channels in Spinal Neurons

Kv2.1 channel subunits underlie delayed rectifier potassium currents that are expressed in neurons throughout the mammalian CNS. We used confocal and electron microscopy to analyze the subcellular localization of these channels in a variety of rat spinal cord neurons, including motoneurons (MNs), interneurons, and dorsal spinocerebellar tract (DSCT) cells, using a commercially available monoclonal antibody against Kv2.1 (Upstate). Kv2.1 immunoreactivity appeared as distinct surface membrane clusters in somatic and proximal dendritic regions. Clusters varied in size and complexity depending on neuron type, with the largest clusters seen on MNs. Quantitative analysis of Kv2.1 channel clusters (n=225 \u27en face\u27 clusters) on MNs revealed a bimodal size distribution including small

Clustering of Kv2.1 Potassium Channels in Spinal Neurons

Kv2.1 channel subunits underlie delayed rectifier potassium currents that are expressed in neurons throughout the mammalian CNS. We used confocal and electron microscopy to analyze the subcellular localization of these channels in a variety of rat spinal cord neurons, including motoneurons (MNs), interneurons, and dorsal spinocerebellar tract (DSCT) cells, using a commercially available monoclonal antibody against Kv2.1 (Upstate). Kv2.1 immunoreactivity appeared as distinct surface membrane clusters in somatic and proximal dendritic regions. Clusters varied in size and complexity depending on neuron type, with the largest clusters seen on MNs. Quantitative analysis of Kv2.1 channel clusters (n=225 \u27en face\u27 clusters) on MNs revealed a bimodal size distribution including small