Ion channel

Ion channels are pore-forming transmembrane proteins that electrically charged particles, ions, the crossing of biomembranes allow. Because of this feature they are also referred to as channel proteins or channel proteins. The transport takes place along the existing electrochemical gradient ( the concentration and potential gradient ). Thus they differ from active transport proteins such as ion pumps, which in turn allow energy consumption among the primary active transport through ion channels. Ion channels are found both in the outer cell membrane and in the membranes of cell organelles such as the tonoplast.

Ion channels are, in interaction with other transport proteins, of universal importance for transport processes across the membrane systems of the cell. These include the regulation of the osmotic activity of the acid -base balance, the absorption and excretion of substances as well as the conduction of excitation in nerve and muscle cells.

It was made possible by the patch-clamp technique to measure a few picoamperes large ion currents through single channel proteins and thus to capture their electrical, kinetic, and other properties.

Biophysical properties

Selectivity and conductivity

Ion channels can be described in terms of their pronounced or lack selectivity for certain ions. The higher the selectivity for one type of ion, the lower the conductivity of the pore open for other ions. We know highly specific channels for

• Cations ( positively charged) as: potassium
• Sodium
• Calcium

• Chloride
• Nitrate
• Malate

Ion channels are often named by their selectivity: potassium, sodium, calcium, or chloride channel.

Then there are the so-called non-specific cation channels such as TRP channels, Eng. transient receptor potential channels, which have a similar conductivity of potassium, sodium and calcium ions.

There are a number of ion channels, such as protons for Thermogenin or voltage-controlled proton- channel. Protons are also actively transported under ATP consumption of proton pump; last not belong to the ion channels. Also not to ion channels in the narrow sense the connexons of gap junctions are counted, the molecules can pass up to about 1 kDa.

Control ( gating)

The conductivity of most ion channels is influenced by the existing environment or related signals drastically, it refers to those channels as controlled (English gated ).

Voltage-gated ion channels

A large class of ionic channels is controlled by the membrane potential ( voltage-dependent ion channels). Thus, for example typical voltage-activated sodium channels during the resting membrane potential of non-conductive, but only when they are activated by depolarization.

Ion channel receptors

Another large class of ion channels activated by ligands, ie by molecules that act as messengers ( ligand-gated ion channels ). Thus, for example of acetylcholine receptor, which plays a role in signal transduction from a nerve to the muscle, conductive in the presence of the neurotransmitter acetylcholine.

Other control mechanisms

• Mechanosensitive ion channels by mechanical stimuli ( eg pressure, vibration) are activated.
• Light- gated ion channels (light gated channels ), eg the channelrhodopsins are activated by light of a specific wavelength
• Temperature- gated ion channels can be activated from specific temperatures

Transport rate

Ion channels have in the open state the greatest transmission rate of any transport proteins, it is generally indicated by 106 to 108 ions per second. Thus they form the fastest membrane transport means, compared with kotransportierenden proteins ( symporters and antiporters ) ( 102 to 104 molecules per second) or ATP-driven pumps ( 100 to 102 ions per second).

Trivia

Roderick MacKinnon, who received the 2003 Nobel Prize in Chemistry for his structural elucidation of ion channels, commissioned the German - American artist Julian Voss - Andreae a sculpture based on his experimental data to create.