Ligand gated ion channels

Ligand-gated ion channels (LGICs) are a group of transmembrane ion-channel proteins that open to allow ions such as Na+, K+, Ca2+, and/or Cl− to pass through the membrane in response to the binding of a chemical messenger (i.e., a ligand), such as a neurotransmitter.

Structure

The LGICs are formed by a pentameric arrangement of subunits. These subunits can be the same (homomeric) or different (heteromeric). Each subunit comprises four transmembrane domains (M1, M2, M3, and M4). The M2 domain lines the ion channel pore.

Function

The primary role of a ligand-gated ion channel is to convert biochemical messages, in the form of neurotransmitter substances, into electrical signals. The ion channels are directly linked to ionotropic receptors. This direct linkage enables the ion channel to open immediately upon the binding of the neurotransmitter, leading to a rapid response.

Classification

Ligand-gated ion channels are classified into three superfamilies which include:

• The Cys-loop receptors
• The Ionotropic glutamate receptors
• The ATP-gated channels

Clinical significance

Defects in LGICs can lead to a range of neurological diseases, such as epilepsy, myasthenia gravis, and hyperekplexia. Furthermore, LGICs are the target of various drugs, including benzodiazepines, barbiturates, ethanol, and nicotine.

See also

• Voltage-gated ion channel
• Receptor (biochemistry)
• Ion channel