What are Ion-Channels?
Ion-channels are a type of membrane protein that exist in nearly all living cells. These proteins allow dissolved salts in the form of charged ions to pass through the impermeable lipid cell membrane. Specialised ‘excitable’ cells contain ion-channels in abundance and can elicit electrical activity as a result of stimulation (examples include: neurons, muscle cells, and some endocrine cells).
How Ion-Channels Work
Ion-channels create a gated pore within a cell. These gates are kept shut but allow certain ions to pass through the channel pore, such as sodium (Na+) or potassium (K+) ions, when stimulated. This stimulation can take the form of mechanical, voltage, and chemical events. The types of gates, an ion channel may take, include:
Voltage-gated — where the ion-channel opens in reaction to the membrane’s electrical potential. Examples of voltage gated channels include those which gate sodium, potassium and calcium ions. Voltage gated calcium channels will open upon depolarisation allowing calcium ions to diffuse through the pore and out of the cell.
Ligand-gated — where the ion-channel’s gate reacts to certain ligand molecules. Ligand molecules act like keys to a gate, opening the ion-channel for certain ions when the molecule attaches to the gate. Examples of ligand gated ions include “nicotinic” Acetylcholine and anion permeable γ-aminobutyric acid which allows GABAA inside the cell.
Other-gated — where the ion-channel’s gate reacts to messengers within the cell membrane rather than from molecules or voltage from outside the cell. Potassium ions are sometimes allowed into the ion-channels in this way. These can act in various ways, one example are light gated channels where the ion-channel are opened by photons stimulating the gate to open.
Where are Ion-Channels Commonly Found in the Body?
The best example of ion-channels used in the body are neurons and their neurotransmitters. Neurons release neurotransmitters when the electrical signal reaches the end of the neuron. Those neurotransmitters binds to the neuron cell on the other side of the synapse through the ion channel receptor. Once the ion channel receptor opens, the electrical signal propagates across the receiving neuron and the process begins again.
