Ion channels are a class of membrane-bound proteins that are present on the surface of all cells as well as on intracellular organelles. Ion channels typically function by creating and maintaining an ion gradient across either cellular or organelle membranes. These channels, comprised of a variety of different protein subunits, contain a pore that can be as narrow as a single atom, allowing for precise control of ion passage.

Ion channels play a critical role in the proper functioning of the human nervous system. Voltage-gated ion channels are present on all neurons and it is the voltage gradient created and maintained by these channels that permits signal propagation; a change in the voltage across the membrane can cause the channel to open or close.

Ion channels, such as those that are present at neuronal synapses, can also be ligand-gated in which the binding of a specific ligand will result in a conformational change in the ion channel resulting in pore opening. In addition to voltage- and ligand-activated ion channels, ion channels can also be activated by heat, temperature, or mechanical stress.

Ion channels have a variety of biological functions, including roles in neuronal signal transmission, muscle contraction, T-cell activation, and insulin release from beta cells. Dysfunctional ion channel activity is the basis of many human diseases. For instance, cystic fibrosis is a result of a genetic mutation in the CFTR gene, which encodes a protein component of a chloride ion channel^[1]. Specific natural or synthetic toxins can also affect the functional ability of ion channels; the puffer fish produces tetrodotoxin (TTX), which inhibits the function of sodium channels and can cause respiratory paralysis and death.

1. Rogan, et al. 2011. Cystic fibrosis transmembrane conductance regulator intracellular processing, trafficking, and opportunities for mutation-specific treatment. Chest. 139(6):1480-90.