User Visitor Login
/images/graph_sv_i.gif
English only
EPFL > FSV > BBP > Channelpedia
Ion channels
References
Reports
SEARCH IN WIKI
Logged in as a Visitor.

K

Potassium channel
Synonyms: . Symbol:

Introductions


Potassium channels represent the most complex class of voltage-gated ion channels from both functional and structural standpoints. Four sequence-related potassium channel genes - shaker, shaw, shab, and shal - have been identified in Drosophila, and each has been shown to have human homolog(s). For example Kv1 (homologous to Drosophila Shaker), Kv2 (Shab), Kv3 (Shaw), Kv4 (Shal), Kv5, Kv6, , Kv8 and the other Kv channels listed in Channelpedia.

Outward rectifiers constitute a large class of voltage-dependent K+ channels. They have six transmembrane domains (S1–S6), one very positively charged (S4), and a typical pore region situated between S5 and S6 [737],[738], [739], [740]. Sequence similarities between members of the Kv family were initially used to define the different subfamilies of alpha subunits. The different members within a given subfamily share only a percentage of 30 –50% with members of others subfamilies. To date 20 functional voltage-gated potassium channels alpha subunits have been described. They belong to six subfamilies designated Kv1 (Shaker), Kv2 (Shab), Kv3 (Shaw), Kv4 (Shal), KvLQT, and EAG. The diversity of potassium channel functions comes from the diversity of potassium channel genes and is increased by alternate splicing (10, 11), regulatory beta subunits (12–14) and heteromultimerization between the different alpha subunits of the same subfamily [741], [733], [734], or sometimes between different subfamilies [742], [743].

Genes


: Potassium channel

RGD ID Chromosome Position Species

Transcripts


Acc No Sequence Length Source

Ontologies


Accession Name Definition Evidence

Interactions


Proteins


Structures


The following is paraphrased from [664]: Kv channels are composed of four subunits that surround the central ion permeation pathway. Each subunit has six transmembrane domains (S1–S6) and a pore region containing the signature sequence GYG characteristic for potassium channels [667], [619]. Post-translational assembly of tetrameric Kv channels takes place in the ER2 membrane; sub- sequently the channels traffic to the plasma membrane [619], [668]. A highly conserved sequence in the cytoplasmic N terminus of Kv channels, the tetramerization domain or T1 domain, has been shown to play an important role in channel assembly [619], [669]. The T1 domain contains some of the molecular determinants for subfamily-specific homo- or heterotetrameric assembly of Kv alpha-subunits [669], [660],[598], [670]. The most striking difference between the T1 domains of Kv1 (Shaker) and Kv2–4 (non-Shaker) channels is the presence of intersubunit-coordinated Zn2+ ions at the assembly interface in non-Shaker channels. The Zn2+ ions are coordinated by a C3H1 motif embedded in a conserved sequence motif (HX5CX20CC) of the T1 domain, which is located near the distal end of the N terminus [671], [672], [673]. These four amino acids are exposed on the subunit interface, with one histidine and two cysteine residues belonging to one subunit and one cysteine residue belonging to the neighboring subunit [671]. The T1 domain facilitates tetrameric assembly of Kv channels. Kv subunits in which the T1 has been deleted have been reported to assemble in a promiscuous way via their transmembrane domains and to form stable, functional channels, but both the rates and the efficiency of channel assembly are significantly lower in the mutant channels as compared with their wild-type counterparts [668], [674]. Heteromeric assembly of channel subunits is a potential source of diversity of K+ channel properties.

Eight different voltage-gated K+ (Kv)3 Shaker-related channel subfamilies (Kv1–Kv6 and Kv8–Kv9) have been identified based on the degree of sequence homology [606]. Fully assembled Kv channels are composed of four α-subunits arranged around a central pore. Each α-subunit consists of six transmembrane segments S1–S6 with a cytoplasmic N and C terminus. The N terminus contains the T1 domain, a tetramerization domain that facilitates the assembly of α-subunits into functional channels. The presence of a T1 domain is not absolutely required for channel assembly because subunits without a T1 domain could also assemble into a functional tetramer, although less efficiently [677], [678], [679]. However, the T1 domain not only promotes but also restricts the formation of possible homo- and heterotetramers by preventing incompatible subunits from assembling [680], [660]. When four compatible T1 domains assemble, they are arranged with the same 4-fold symmetry as the transmembrane segments, forming a hanging gondola structure [681].

Distributions


Expressions


Voltage-gated potassium channels of the Kv family are strongly expressed in the mammalian central nervous system, in the immune system, in muscle cells and in many other cell types. Most neurons express multiple Kv channel subtypes belonging to one or more subfamilies [496], [638], [665].

Functionals


Their diverse functions include regulating neurotransmitter release, heart rate, insulin secretion, neuronal excitability, epithelial electrolyte transport, smooth muscle contraction, and cell volume.

Voltage gated potassium channels play a key role in controlling neuronal excitability and regulate a variety of electrophysiological properties, such as the interspike membrane potential, the waveform of the action potential and the firing frequency [666].

Kinetics


Models


[1] HHK (Model ID = 1)

AnimalSquid 28
CellType giant Axon
Age 0 Days
Temperature9.3°C
Reversal -78.0 mV
Ion K +
Ligand ion
Reference A L Hodgkin et. al; Bull. Math. Biol. 1990
mpower 4.0
mAlpha (0.01*(10-v))/(exp((10-v)/10) - 1.0) If v neq 10
mBeta 0.125 * (exp(-v/80))

MOD xml channelML

[2] KSlow (Model ID = 30)

Animalrat 118
CellType Neocortical L5PC
Age 15 Days
Temperature23.0°C
Reversal -65.0 mV
Ion K +
Ligand ion
Reference A Korngreen et. al; J. Physiol. (Lond.) 2000 Jun 15
mpower 2.0
mInf (1/(1 + exp(-(v+14)/14.6)))
mTau (1.25+175.03*exp(-v * -0.026)) If v lt -50
mTau (1.25+13*exp(-v*0.026)) If v gteq -50
hpower 1.0
hInf 1/(1 + exp(-(v+54)/-11))
hTau 360+(1010+24*(v+55))*exp(-((v+75)/48)^2)

MOD xml channelML

[3] KSlow_S (Model ID = 31)

Animalrat 121
CellType Neocortical L5PC
Age 15 Days
Temperature23.0°C
Reversal -65.0 mV
Ion K +
Ligand ion
Reference A Korngreen et. al; J. Physiol. (Lond.) 2000 Jun 15
mpower 2.0
mInf (1/(1 + exp(-((v-21)+14)/14.6)))
mTau (1.25+175.03*exp(-(v-21) * -0.026)) If v lt -29
mTau (1.25+13*exp(-(v-21)*0.026)) If v gteq -29
hpower 1.0
hInf 1/(1 + exp(-((v-21)+54)/-11))
hTau 360+(1010+24*((v-21)+55))*exp(-(((v-21)+75)/48)^2)

MOD xml channelML

[4] Kfast (Model ID = 32)

Animalrat 124
CellType Neocortical L5PC
Age 15 Days
Temperature23.0°C
Reversal -65.0 mV
Ion K +
Ligand ion
Reference A Korngreen et. al; J. Physiol. (Lond.) 2000 Jun 15
mpower 1.0
mInf 1/(1 + exp(-(v+47)/29))
mTau (0.34+0.92*exp(-((v+71)/59)^2))
hpower 1.0
hInf 1/(1 + exp(-(v+56)/-10))
hTau (8+49*exp(-((v+73)/23)^2))

MOD xml channelML

[5] K_Pst (Model ID = 48)

Animalrat 196
CellType Neocortical L5PC
Age 15 Days
Temperature23.0°C
Reversal -65.0 mV
Ion K +
Ligand ion
Reference A Korngreen et. al; J. Physiol. (Lond.) 2000 Jun 15
mpower 2.0
mInf (1/(1 + exp(-(v+1)/12)))
mTau (1.25+175.03*exp(-v * -0.026))/qt If v lt -50
mTau ((1.25+13*exp(-v*0.026)))/qt If v gteq -50
hpower 1.0
hInf 1/(1 + exp(-(v+54)/-11))
hTau (360+(1010+24*(v+55))*exp(-((v+75)/48)^2))/qt

MOD

[6] K_Tst (Model ID = 49)

Animalrat 199
CellType Neocortical L5PC
Age 15 Days
Temperature23.0°C
Reversal -85.0 mV
Ion K +
Ligand ion
Reference A Korngreen et. al; J. Physiol. (Lond.) 2000 Jun 15
mpower 4.0
mInf 1/(1 + exp(-(v+0)/19))
mTau (0.34+0.92*exp(-((v+71)/59)^2))/qt
hpower 1.0
hInf 1/(1 + exp(-(v+66)/-10))
hTau (8+49*exp(-((v+73)/23)^2))/qt

MOD

[7] KdShu2007 (Model ID = 50)

Animalrat 202
CellType L5PC
Age 17 Days
Temperature23.0°C
Reversal -85.0 mV
Ion K +
Ligand ion
Reference Yousheng Shu et. al; Proc. Natl. Acad. Sci. U.S.A. 2007 Jul 3
mpower 1.0
mInf 1-1/(1+exp((v- -43)/8))
mTau 0.6
hpower 1.0
hInf 1/(1+exp((v- -67)/7.3))
hTau 1500

MOD

References


[262 : 2185861]
[264 : 10856117]
[321 : 19299025]
[375 : 20557422]
[376 : 20551590]
[666 : 1202319]
[496 : 10414301]
[665 : 2457185]
[638 : 9423171]
[598 : 1519059]
[619 : 11551188]
[660 : 7559593]
[664 : 19074135]
[669 : 15664174]
[670 : 8338669]
[671 : 9886290]
[672 : 12372826]
[673 : 12754210]
[674 : 8702552]
[677 : 19717558]
[679 : 10716722]
[680 : 8011897]
[681 : 10956024]
[733 : 8361540]
[734 : 8361541]
[737 : 8271269]
[738 : 8038378]
[739 : 7538310]
[740 : 7748553]
[741 : 2317379]
[742 : 7556617]
[743 : 8816716]
[1499 : 17581873]

Credits


Editor : Admin.

Contributors : Rajnish Ranjan, Michael Schartner

To cite : [Editor], [Contributors]. Accessed on [Date] Channelpedia , http://channelpedia.epfl.ch/ionchannels/188