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Voltage Gated Ion Channels and Ligand Gated Ion Channels

Discover the differences between voltage gated ion channels and ligand gated ion channels. Find out which molecules pass through these types of transporter systems to enter and leave cells.

The membrane of a cell is semi-permeable. It allows certain molecules to enter or leave the cell, while preventing other molecules from crossing the phospholipid bilayer. Molecules which have a path through this barrier usually use a specific way to get in or out. Some are able to pass directly through the cell membrane, such as water molecules. Other more complex molecules, as well as ions which must be tightly regulated, travel through channels to move between the interior and exterior of the cell. Voltage gated ion channels and ligand gated ion channels are two such channels.

Voltage Gated Ion Channels

Voltage gated ion channels transport ions across the cell membrane in response to a change in the electrical potential between the interior environment and the external environment of the cell. This change in membrane potential causes a protein subunit of the ion channel to alter its orientation. As a result, the channel is open or closed to ion flow. One type of voltage gated ion channel is the potassium channel. It regulates the concentration of potassium ions in the cell. The sodium channel is another voltage gated channel. Both of these channels are present in the cell membrane of all cells.

Ligand Gated Ion Channels

Ligand gated ion channels transport ions across the cell membrane in response to an external molecule that binds to the channel. When this molecule comes into contact with the channel, a portion of the channel changes conformation, allowing ions to flow through. Similarly, the channel can close, preventing ions from traveling through the membrane. One example of a ligand gated ion channel is the nicotinic acetylcholine receptor, which is responsible for signaling muscle contraction. The ligand is the molecule acetylcholine, which is released by the motor neuron. It opens the ion channel in the receptor of the muscle cell, triggering the flow of sodium, potassium, and calcium ions.

Reference:

Nelson, David L. Lehninger Principles of Biochemistry 4th ed. W.H. Freeman and Company. 2005

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