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Potassium voltage-gated channel, shaker-related subfamily, member 3, also known as KCNA3 or Kv1.3, is a protein that in humans is encoded by the ''KCNA3'' gene.〔(【引用サイトリンク】 url = http://www.ncbi.nlm.nih.gov/sites/entrez?Db=gene&Cmd=ShowDetailView&TermToSearch=3738 )〕 Potassium channels represent the most complex class of voltage-gated ion channels from both functional and structural standpoints. Their diverse functions include regulating neurotransmitter release, heart rate, insulin secretion, neuronal excitability, epithelial electrolyte transport, smooth muscle contraction, and cell volume. 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). This gene encodes a member of the potassium channel, voltage-gated, shaker-related subfamily. This member contains six membrane-spanning domains with a shaker-type repeat in the fourth segment. It belongs to the delayed rectifier class, members of which allow nerve cells to efficiently repolarize following an action potential. It plays an essential role in T cell proliferation and activation. This gene appears to be intronless and is clustered together with KCNA2 and KCNA10 genes on chromosome 1.〔 == Function == ''KCNA3'' encodes the voltage-gated Kv1.3 channel, which is expressed in T and B lymphocytes.〔 All human T cells express roughly 300 Kv1.3 channels per cell along with 10-20 calcium-activated KCa3.1 channels. Upon activation, naive and central memory T cells increase expression of the KCa3.1 channel to approximately 500 channels per cell, while effector-memory T cells increase expression of the Kv1.3 channel.〔〔 Among human B cells, naive and early memory B cells express small numbers of Kv1.3 and KCa3.1 channels when they are quiescent, and augment KCa3.1 expression after activation. In contrast, class-switched memory B cells express high numbers of Kv1.3 channels per cell (about 1500/cell) and this number increases after activation.〔 Kv1.3 is physically coupled through a series of adaptor proteins to the T-cell receptor signaling complex and it traffics to the immunological synapse during antigen presentation. However, blockade of the channel does not prevent immune synapse formation.〔 Kv1.3 and KCa3.1 regulate membrane potential and calcium signaling of T cells.〔 Calcium entry through the CRAC channel is promoted by potassium efflux through the Kv1.3 and KCa3.1 potassium channels.〔〔 Blockade of Kv1.3 channels in effector-memory T cells suppresses calcium signaling, cytokine production (interferon-gamma, interleukin 2) and cell proliferation.〔〔〔 In vivo, Kv1.3 blockers paralyze effector-memory T cells at the sites of inflammation and prevent their reactivation in inflamed tissues. In contrast, Kv1.3 blockers do not affect the homing to and motility within lymph nodes of naive and central memory T cells, most likely because these cells express the KCa3.1 channel and are, therefore, protected from the effect of Kv1.3 blockade.〔 Kv1.3 has been reported to be expressed in the inner mitochondrial membrane in lymphocytes. The apoptotic protein Bax has been suggested to insert into the outer mitochondrial membrane and occlude the pore of Kv1.3 via a lysine residue. Thus, Kv1.3 modulation may be one of many mechanisms that contribute to apoptosis.〔〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「KCNA3」の詳細全文を読む スポンサード リンク
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