Ligand-gated ion channels bind a ligand, such as a neurotransmitter, and open a channel through the membrane that allows specific ions to pass through. To form a channel, this type of cell-surface receptor has an extensive membrane-spanning region. To interact with the phospholipid fatty acid tails that form the center of the plasma membrane, many of the amino acids in the membrane-spanning region are hydrophobic. Conversely, the amino acids that line the inside of the channel are hydrophilic to allow for the passage of water or ions. When a ligand binds to the extracellular region of the channel, there is a conformational change in the protein’s structure that allows ions such as sodium, calcium, magnesium, and hydrogen to pass through. The ligand-binding region is known as an allosteric site. It is located away from the actual ion channel but induces a conformational change in the channel to cause it to open.

Note that ligand-gated ion channels are not to be confused with voltage-gated channels, which only rely on a difference in membrane potential. Voltage-gated ion channels respond to a change in membrane potential by undergoing a conformational change that allows the channel to open. They are usually selective for a specific type of ion.

One commonplace to find gated ion channels is in electrically excitable cells like neurons, which need to react very quickly to a stimulus. When a gated ion channel opens, it rapidly lets ions move through the channel, either into or out of the cell depending on the concentration gradient of ions across the plasma membrane (AKA the membrane potential). This converts an extracellular ligand signal into an intracellular electrical signal and will cause a change in the electrical properties of the cell.