Inwardly rectifying potassium channel

Inwardly rectifying potassium channels (Kir) are a specific subset of potassium channels. Inward rectification refers to the property of these channels to allow more inward current (into the cell) than outward current (out of the cell). This unique property is crucial for maintaining resting membrane potential, as well as other physiological processes such as the regulation of heart rate and insulin secretion.

Structure

Inwardly rectifying potassium channels are tetramers, composed of four subunits that span the cell membrane. Each subunit consists of two transmembrane domains (M1 and M2), with a pore-forming loop between them. The N- and C-termini of the protein are located on the cytoplasmic side of the membrane.

Function

The primary function of Kir channels is to regulate the flow of potassium ions across the cell membrane. They allow potassium ions to flow into the cell, but not out. This inward flow of potassium ions helps to maintain the resting membrane potential of the cell.

In addition to maintaining resting membrane potential, Kir channels also play a role in other physiological processes. For example, they are involved in the regulation of heart rate and insulin secretion. In the heart, Kir channels help to repolarize the cardiac muscle cells after each beat. In the pancreas, they are involved in the secretion of insulin in response to increased blood glucose levels.

Types

There are seven known families of Kir channels, designated Kir1.x through Kir7.x. Each family is further divided into subtypes, based on their specific properties and functions. For example, Kir2.x channels are involved in maintaining the resting membrane potential, while Kir6.x channels are involved in insulin secretion.

Clinical significance

Mutations in the genes encoding Kir channels can lead to a variety of diseases, known as channelopathies. These include Andersen-Tawil syndrome, Bartter syndrome, and neonatal diabetes. In addition, drugs that target Kir channels are used in the treatment of several conditions, including hypertension, angina, and arrhythmia.

See also

• Potassium channel
• Ion channel
• Channelopathy