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.
Muennich
Elizabeth A L
EA
Department of Anatomy and Physiology, Wright State University, Dayton, OH 45435, USA.
Fyffe
R E W
RE
D000344:Afferent Pathways / Q000378:metabolism / Q000648:ultrastructure; D000818:Animals; D051668:Delayed Rectifier Potassium Channels; D007150:Immunohistochemistry; D007395:Interneurons / Q000378:metabolism / Q000648:ultrastructure; D008297:Male; D016253:Microscopy, Immunoelectron; D009046:Motor Neurons / Q000378:metabolism* / Q000648:ultrastructure; D015221:Potassium Channels / Q000378:metabolism*; D024642:Potassium Channels, Voltage-Gated; D051381:Rats; D017207:Rats, Sprague-Dawley; D051669:Shab Potassium Channels; D013116:Spinal Cord / Q000378:metabolism* / Q000648:ultrastructure; D013569:Synapses / Q000378:metabolism*
D051668:Delayed Rectifier Potassium Channels; C496991:Kcnb1 protein, rat; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D051669:Shab Potassium Channels