Who or what are Ion Channels?
Ion channels are proteins that act as the doorman of the cell, controlling the flow of small
charged molecules known as chemical ions into and out of the cell. They are proteins that sit
Ion channels are proteins that act as the doorman of the cell...
in across the membranes of all cells, forming a door in the wall that protects the inside of
the cell from the harsh environment outside. This means that the cell needs a way to control
what enters through this door and what exits. The ions that these channels transport are needed
by the cell for many of its activities, including those as important as growth and reproduction.
There are several hundreds types of ion channels and each one may work with only one or two ions.
If they fail to function correctly, the effects are very damaging to the cell and hence, to an
individual. Indeed, the malfunction of these channels causes the conditions known collectively
as 'Channelopathies'.
Below: Schematic drawing of an ion channel
(palid orange) embedded in the membrane. Ions can be found on either side
of the membrane but they must pass through the ion channel to enter
or exit the cell.
What do Ion Channels do?
So, ion channels direct the flow of ions between the inside and outside of the cell and a cell
cannot survive without them. Moreover, if they do not function correctly they cause severe problems
in an individual
Ion channels are normally found on the surfaces of cells, inserted in the membrane. They usually
if the ion channels do not function correctly they cause severe problems...
form a cylindrical or tube-like structure in the membrane. The pore at the centre of the ion channel
is where the ions and water pass through the membrane. It is also here where the ion channel decides
which types of ions it will allow through.
The flow of ions through the pores is controlled by gates. As might be imagined, gating is the
way in which a channel opens and closes its pore. A gate can be completely open or closed, or it
may be in a intermediate where it can decide whether or not to permit the entry of an ion: on the
latch so to speak.
While different gates are influenced by distinct factors, some of these gates are sensitive to
the electrical impulses received by cells. Thus, ion channels provide a way to regulate nervous
excitability in the central and peripheral nervous system, and in the muscles.
In stressing the importance of ion channels, we only have to consider that they are responsible
for regulating the amount of water that enters a cell. Too much water and a cell may burst, not
enough and it may shrink and become too sticky.
Ion channels are also important in the internal messages that cell transmits, known as
"intracellular signalling". These signals often involve changes in the amount of calcium ions
(Ca2+) in the cell, which are produced by the passage of Ca2+ ions through Calcium channels.
These processes are particular important in muscle contraction and nerve transmission and help
the cell to adapt its environment.
Ion channels act exceedingly rapidly when compared to normal human activities. Many channels
are capable of allowing ions through at the rate of 100 million ions each second, and many of
these channels stay open less than a millisecond at a time before closing again. This rapid flow
of ions enables the organism to exert a very a fine level of control over what goes in and out
of a nerve or muscle cell.
The first ion channels discovered were the so-called voltage-gated ion channels in nerve and
muscle cells. These include ion channels for sodium, potassium, and calcium, which must open and
close for neurons to conduct electrical impulses.