science

Voltage-gated potassium channel

Voltage-gated potassium channel is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Voltage-gated potassium channel rather than just read about it. In short: Voltage-gated potassium channels (VGKCs) are transmembrane channels specific for potassium and sensitive to voltage changes in the cell's membrane potential. During action potentials, they play a crucial role in returning the depolarized cell to a resting state.

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Reference excerpt

Voltage-gated potassium channels (VGKCs) are transmembrane channels specific for potassium and sensitive to voltage changes in the cell's membrane potential. During action potentials, they play a crucial role in returning the depolarized cell to a resting state.

Classification

Alpha subunits Alpha subunits form the actual conductance pore. Based on sequence homology of the hydrophobic transmembrane cores, the alpha subunits of voltage-gated potassium channels are grouped into 12 classes. These are labeled Kvα1-12. The following is a list of the 40 known human voltage-gated potassium channel alpha subunits grouped first according to function and then subgrouped according to the Kv sequence homology classification scheme:

Delayed rectifier slowly inactivating or non-inactivating

Kvα1.x - Shaker-related: Kv1.1 (KCNA1), Kv1.2 (KCNA2), Kv1.3 (KCNA3), Kv1.5 (KCNA5), Kv1.6 (KCNA6), Kv1.7 (KCNA7), Kv1.8 (KCNA10) Kvα2.x - Shab-related: Kv2.1 (KCNB1), Kv2.2 (KCNB2) Kvα3.x - Shaw-related: Kv3.1 (KCNC1), Kv3.2 (KCNC2) Kvα7.x: Kv7.1 (KCNQ1) - KvLQT1, Kv7.2 (KCNQ2), Kv7.3 (KCNQ3), Kv7.4 (KCNQ4), Kv7.5 (KCNQ5) Kvα10.x: Kv10.1 (KCNH1)

A-type potassium channel rapidly inactivating

Kvα1.x - Shaker-related: Kv1.4 (KCNA4) Kvα4.x - Shal-related: Kv4.1 (KCND1), Kv4.2 (KCND2), Kv4.3 (KCND3)

Outward-rectifying Kvα10.x: Kv10.2 (KCNH5)

Inwardly-rectifying Passes current more easily in the inward direction (into the cell, from outside).

Kvα11.x - ether-a-go-go potassium channels: Kv11.1 (KCNH2) - hERG, Kv11.2 (KCNH6), Kv11.3 (KCNH7)

Slowly activating Kvα12.x: Kv12.1 (KCNH8), Kv12.2 (KCNH3), Kv12.3 (KCNH4)

Modifier/silencer Unable to form functional channels as homotetramers but instead heterotetramerize with Kvα2 family members to form conductive channels.

Kvα5.x: Kv5.1 (KCNF1) Kvα6.x: Kv6.1 (KCNG1), Kv6.2 (KCNG2), Kv6.3 (KCNG3), Kv6.4 (KCNG4) Kvα8.x: Kv8.1 (KCNV1), Kv8.2 (KCNV2) Kvα9.x: Kv9.1 (KCNS1), Kv9.2 (KCNS2), Kv9.3 (KCNS3)

Beta subunits Beta subunits are auxiliary proteins that associate with alpha subunits, sometimes in a α4β4 stoichiometry. These subunits do not conduct current on their own but rather modulate the activity of Kv channels.

Kvβ1 (KCNAB1) Kvβ2 (KCNAB2) Kvβ3 (KCNAB3) minK (KCNE1) MiRP1 (KCNE2) MiRP2 (KCNE3) MiRP3 (KCNE4) KCNE1-like (KCNE1L) KCNIP1 (KCNIP1) KCNIP2 (KCNIP2) KCNIP3 (KCNIP3) KCNIP4 (KCNIP4) Proteins minK and MiRP1 are putative hERG beta subunits.

Animal research The voltage-gated K+ channels that provide the outward currents of action potentials have similarities to bacterial K+ channels. These channels have been studied by X-ray diffraction, allowing determination of structural features at atomic resolution. The function of these channels is explored by electrophysiological studies. Genetic approaches include screening for behavioral changes in animals with mutations in K+ channel genes. Such genetic methods allowed the genetic identification of the "Shaker" K+ channel gene in Drosophila before ion channel gene sequences were well known. Study of the altered properties of voltage-gated K+ channel proteins produced by mutated genes has helped reveal the functional roles of K+ channel protein domains and even individual amino acids within their structures.

Structure Typically, vertebrate voltage-gated K+ channels are tetramers of four identical subunits arranged as a ring, each contributing to the wall of the trans-membrane K+ pore. Each subunit is composed of six membrane spanning hydrophobic α-helical sequences, as well as a voltage sensor in S4. The intracellular side of the membrane contains both amino and carboxy termini. The high resolution crystallographic structure of the rat Kvα1.2/β2 channel has recently been solved (Protein Databank Accession Number 2A79), and then refined in a lipid membrane-like environment (PDB: 2r9r).

Selectivity

Voltage-gated K+ channels are selective for K+ over other cations such as Na+. There is a selectivity filter at the narrowest part of the transmembrane pore. Channel mutation studies have revealed the parts of the subunits that are essential for ion selectivity. They include the amino acid sequence (Thr-Val-Gly-Tyr-Gly) or (Thr-Val-Gly-Phe-Gly) typical to the selectivity filter of voltage-gated K+ channels. As K+ passes through the pore, interactions between potassium ions and water molecules are prevented and the K+ interacts with specific atomic components of the Thr-Val-Gly-[YF]-Gly sequences from the four channel subunits [1]. It may seem counterintuitive that a channel should allow potassium ions but not the smaller sodium ions through. However in an aqueous environment, potassium and sodium cations are solvated by water molecules. When moving through the selectivity filter of the potassium channel, the water-K+ interactions are replaced by interactions between K+ and carbonyl groups of the channel protein. The diameter of the selectivity filter is ideal for the potassium cation, but too big for the smaller sodium cation. Hence the potassium cations are well "solvated" by the protein carbonyl groups, but these same carbonyl groups are too far apart to adequately solvate the sodium cation. Hence, the passage of potassium cations through this selectivity filter is strongly favored over sodium cations.

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Illustrations

Worked examples

Example 1 — a first encounter with Voltage-gated potassium channel

Start with the simplest possible case. Write down what Voltage-gated potassium channel claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Voltage-gated potassium channel before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Voltage-gated potassium channel ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Voltage-gated potassium channel

In research: Voltage-gated potassium channel appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Voltage-gated potassium channel in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Voltage-gated potassium channel is common in secondary-school and first-year university syllabi. It links to neighbouring topics Electrophysiology, Potassium channels, Voltage-gated ion channels, so understanding it makes those chapters shorter.
In everyday life: Look for Voltage-gated potassium channel outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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