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potassium voltage-gated channel, delayed-rectifier, subfamily S, member 1
KV9.1 is member 1 of subfamily S of potassium voltage-gated delayed-rectifier channels, encoded by the gene KCNS1.
Alpha subunits are of 2 types: those that are functional by themselves and those that are electrically silent but capable of modulating the activity of specific functional alpha subunits. The protein encoded by KCNS1 is not functional by itself but can form heteromultimers with member 1 and with member 2 (and possibly other members) of the Shab-related subfamily of potassium voltage-gated channel proteins. This gene belongs to the S subfamily of the potassium channel family.
In contrast to the genes in the other subfamilies, members of the Kv8 and Kv9 subfamilies have been found to be incapable of forming functional channels when expressed either in oocytes or cell lines. Moreover, these mammalian genes appear to have no Drosophila homologs. 
Kcns1 : potassium voltage-gated channel, delayed-rectifier, subfamily S, member 1
Kv2.1 and Kv2.2 Co-assembly
Since previous studies have suggested that Kv9.1 function is linked to coassembly with Kv2.1 and Kv2.2 subunits, we investigated whether Kv9.1 and Kv2 subunits are coexpressed in DRG neurons. To achieve this, we performed ISH for Kv9.1/Kv2.1 (left) and Kv9.1/Kv2.2 (right) in adjacent DRG sections and were able to directly observe colocalization of these mRNAs in single medium-large neurons (arrows). Examining the Kv9.1-positive population, we found that 48.6 and 76.9% of cells coexpressed Kv2.1 or Kv2.2, respectively. The presence of both Kv2 subunits was documented in more than a third of all Kv9.1-positive neurons (36.7%), while only a small number did not express any Kv2 subunit (11.25%) 
The Kv9.1 gene encodes a potassium channel alpha subunit that is expressed in a variety of neurons, including those of the inferior colliculus. When cRNA encoding this subunit is injected into Xenopus oocytes, no functional channels are expressed. Kv9.1 isolated from a rat brain cDNA library alters the kinetics and the voltage-dependence of activation and inactivation of Kv2.1, a channel subunit that generates slowly inactivating delayed rectifier potassium currents. The rate of activation of Kv2.1 is slowed by co-expression with Kv9.1. With Kv2.1 alone, the amplitude of evoked currents increases monotonically with increasing command potentials. In contrast, when Kv2.1 is co-expressed with Kv9.1, the amplitude of currents increases with increasing depolarization up to potentials of only ∼+60 mV, after which increasing depolarization results in a decrease in current amplitude. 
Kv9.1 and Kv9.2 are neuronal modulatory alpha subunits that define a structural family designated as Kv9. They modulate Kv2.alpha subunits but have no functional activity by themselves. 
Expression of Kv9.1 in DRG sections of Rats
We first examined the expression of Kv9.1 transcripts in lumbar DRG sections of naive rats, using ISH. Size-frequency analysis revealed that Kv9.1 mRNA was robustly expressed in medium-large (>30 μm diameter, 89.7 ± 1.5%), but not small (<30 μm diameter, 5.6 ± 1.4%) neurons 
Kv9.1 and Kv9.2, two known members of the Kv9 subfamily, appear to be expressed diffusely in cells of the inferior colliculus .
Kv9.1 Expression in Rat Brain
High levels of expressions are found in the olfactory bulb, cerebral cortex, hippocampal formation, habenula, basolateral amygdaloid nuclei, and cerebellum. Interestingly Kv9.1 and Kv9.2 colocalized with Kv2.1 and/or Kv2.2 α subunits in several regions of the brain 
Inhibitor of Neuronal Excitability
Our study is the first one to address the effect of Kv9.1 in vivo and our results strongly suggest that, in sensory neurons, Kv9.1 is an inhibitor of neuronal excitability . Interestingly, Kv9.1 is not a pore-forming subunit and therefore its influence on sensory neuron excitability must be indirect 
K+ channel functions are included in very diverse processes such as neuronal integration, cardiac pacemaking, muscle contraction, and hormone secretion in ex- citable cells , as well as in cell proliferation, cell volume regulation, and lymphocyte differentiation .
Kv9.1 and Kv9.2 modulate Kv2.alpha subunits but have no functional activity by themselves . I.e., the kinetics of activation and the voltage-dependence of Kv2.1 currents are altered by such co-expression with Kv9.1 .
Of particular interest, we illustrate that Kv9.1 dysfunction can also trigger a form of stimulus-dependent hyperexcitability in sensory neurons. This firing did not depend on any CNS connection as it was observed in axons that were centrally disconnected 
Our results propose that Kv9.1 downregulation after nerve injury may be the molecular switch controlling myelinated sensory neuron hyperexcitability. Intriguingly, a recent wide-genome association screen in humans identified a Kv9.1 polymorphism associated with susceptibility to develop chronic neuropathic pain after back surgery or leg amputation, suggesting that the mechanisms described in our studies will be of direct clinical relevance to human pain  
Kv9.1 Kinetics affect Kv2.2 and Kv1.3
 It is likely that the association of Kv9.1 with functional channel subunits such as Kv2.1 alters their properties in ways other than the relatively minor changes in kinetics and voltage dependence described here. In particular, ‘silent’ subunits, such as Kv9.1, may add new sites for modulation by protein kinases and other second messengers, or may target the resultant channel complex to specific subcellular locations within a neuron. Determination of its real function in neurons, such as those of the inferior colliculus, may eventually require investigation of native potassium currents and firing patterns in cells in which the Kv9.1 gene has been deleted 
Kv9.1 interacts with Kv2.1 in CHO cells
In our experiments, both hKv9.1 and hKv9.3 slowed the deactivation and inactivation of hKv2.1-dependent currents, in keeping with previous results (18, 26). Interestingly, with the cotransfection of either electrically silent subunit with hKv2.1, inactivation and deactivation time courses more closely matched those measured from native human lens cells than did the time courses measured from hKv2.1 alone. Transfection with either hKv2.1-hKv9.1 or hKv2.1-hKv9.3 fusion proteins produces about the same slowing of activation as cotransfection of unfused subunits 
Editor : Admin.
Contributors : Rajnish Ranjan, Michael Schartner, Nitin Khanna
To cite : [Editor], [Contributors]. Accessed on [Date] Channelpedia , http://channelpedia.epfl.ch/ionchannels/30