Ion Channels

Hello everyone,

Today I will be writing about Ion Channels

Certain cells, commonly called excitable cells, are unique because of their ability to generate electrical signals. Although several types of excitable cells exist — including neurons, muscle cells, and touch receptor cells — all of them use ion channel receptors to convert chemical or mechanical messages into electrical signals.

Ion channels are pore-forming membrane proteins whose 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 acrosss ecretory and epithelial cells, and regulating cell volume. Ion channels are present in the membranes of all cells. Ion channels are considered to be one of the two traditional classes of ionophoric proteins, with the other class known as ion transporters (including the sodium-potassium pump, sodium-calcium exchanger, and sodium-glucose transport proteins, amongst others)

The three main groups of ion channels are

 1) the voltage-gated channels such as the sodium and potassium channels of the nerve axons and nerve terminals,

 2) the extracellular ligand-activated channelswhich includes channels such as GABA and glycine receptor channels, most of which are regulated by ligands that are "neurotransmitters". These channels are often named according to the ligand they bind to. 3) Intracellular ligand-gated ion channels.

     

 Ion channel Receptors are usually multimeric proteins located in the plasma membrane. Each of these proteins arranges itself so that it forms a passageway or pore extending from one side of the membrane to the other. These passageways, or ion channels, have the ability to open and close in response to chemical or mechanical signals. When an ion channel is open, ions move into or out of the cell in single-file fashion. Individual ion channels are specific to particular ions, meaning that they usually allow only a single type of ion to pass through them. Both the amino acids that line a channel and the physical width of the channel determine which ions are able to wiggle through from the cell exterior to its interior, and vice versa. The opening of an ion channel is a fleeting event. Within a few milliseconds of opening, most ion channels close and enter a resting state, where they are unresponsive to signals for a short period of time.

Function of Ion channels

•        Mediate the generation, conduction and transmission of electrical signals in the                   nervous system.
•        Control the release of neurotransmitters and hormones
•        Initiate muscle contraction
•        Transfer small molecules between cells (gap junctions)
•        Mediate fluid transport in secretory cells
•        Control motility of growing and migrating cells
•        Provide selective permeability properties important for various intracellular organelles.

     -Dixy