Ion channel

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Ion channels are pore-forming membrane proteins that allow ions to pass through the channel pore. Their functions include establishing a resting membrane potential, shaping action potentials and other electrical signals by gating the flow of ions across the cell membrane, controlling the flow of ions across secretory and epithelial cells, and regulating cell volume. Ion channels are present in the membranes of all cells. Ion channels are one of the two classes of jonophoric proteins, the other being ion transporters.

The study of ion channels often involves biophysics, electrophysiology, and pharmacology, while using techniques including voltage clamp, patch clamp, immunohistochemistry, X-ray crystallography, fluoroscopy, and RT-PCR. Their classification as molecules is referred to as channelomics.

Basic features

There are two distinctive features of ion channels that differentiate them from other types of ion transport protein:

One. The rate of ion transport through the channel is very high (often one hundred million ions per second or greater).

Two. Ions pass through channels down their electrochemical gradient, which is a function of ion concentration and membrane potential, "downhill", without the input (or help) of metabolic energy (e.g. ATP, co-transport mechanisms, or active transport mechanisms).

Ion channels are located within the membrane of all excitable cells, and of many intracellular organelles. They are often described as narrow, water-filled tunnels that allow only ions of a certain size and/or charge to pass through. This characteristic is called selective permeability. The archetypal channel pore is just one or two atoms wide at its narrowest point and is selective for specific species of ion, such as sodium or potassium. However, some channels may be permeable to the passage of more than one type of ion, typically sharing a common charge: positive (cations) or negative (anions). Ions often move through the segments of the channel pore in a single file nearly as quickly as the ions move through the free solution. In many ion channels, passage through the pore is governed by a "gate", which may be opened or closed in response to chemical or electrical signals, temperature, or mechanical force.

Ion channels are integral membrane proteins, typically formed as assemblies of several individual proteins. Such "multi-subunit" assemblies usually involve a circular arrangement of identical or homologous proteins closely packed around a water-filled pore through the plane of the membrane or lipid bilayer. For most voltage-gated ion channels, the pore-forming subunit (s) are called the alpha subunit, while the auxiliary subunits are denoted beta, gamma, and so on.

Biological role

Diversity

Classification by gating

Voltage-gated

Ligand-gated (neurotransmitter)

Lipid-gated

Other gating

Some potassium channels:

Calcium-activated potassium

Light-gated channels like

Classification by type of ions

Potassium channels

Calcium-activated potassium channels e.g., BKCa or Maxik, SK, etc.

Two-pore-domain potassium

Sodium channels

Epithelial sodium channels

Proton channels

Classification by cellular localization

Plasma membrane channels

Intracellular channels, which are further classified into different organelles

Other classifications

Detailed structure

Pharmacology

Ion channel blockers

Ion channel activators

Diseases

History

Overview

The document details the functions and structures of ion channels, emphasizing their importance in cellular processes including action potentials in neurons and muscle contraction. It also explores the diverse classifications of ion channels based on gating mechanisms and ion selectivity.

Key Points

1Ion channels are vital for establishing resting membrane potentials and shaping action potentials
2There are numerous types of ion channels classified by gating and ion specificity
3Ion channels play key roles in various physiological processes and are targets for drug development
4Voltage-gated and ligand-gated channels are among the primary classifications of ion channels
5Ion channels exhibit selective permeability to specific ions, crucial for cellular function.

Details

Category: Biology and Natural Sciences

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