Ion channels are intrinsic proteins with a distinctive pore running through the middle. They are found in lipid bilayer membranes of cells and organelles. They allow the passage of ions in and out of cells and organelles via various modes of transport such as facilitated diffusion and active transport, and also allow a voltage gradient to be maintained.Ion channels are selective by the size and charge of the Ion. The pore must be narrow enough to only allow the selected ion through causing close contact between the ion and the channel.The narrowest part of the channel is called the selectivity filter. One way in which ion channels can be categorized is by their gating.
There are three types of ion gated channels:
Voltage Gated ion channels
Voltage-gated ions channels are important in nerve and muscles cells. They are based around the movement of charges. For these particular cells they involve the movement of sodium (Na+) and potassium (K+) ions. These ions are important at creating action potentials by the depolarising, repolarising and hyperpolarising of the internal cell membrane in relation to the outside. The Potassium gated ion channels are slower at opening and closing and this is what causes hyperpolarisation of the membrane.
Ligand Gated ion channels
Ligand-gated ion channels are found on the postsynaptic membrane at a neuromuscular junction. In this case, the postsynaptic membrane is that of a muscle cell. The channel is opened and closed by the binding and releasing of the neurotransmitter acetylcholine. The receptor on the channel protein is called the nicotinic acetylcholine receptor and allows the passage of K+ out of the cell and Na+ into the cell.
Intracellular messenger-gated ion channels
By measuring the current of a single ion channel in a single cell we can learn three things: The conductance of the channel, the open state probability of the channel, and the selectivity of the channel (i.e. which ions move across the channel).