Kir2

Kir2 refers to a family of inwardly rectifying potassium ion channels, also known as G protein-coupled inwardly rectifying potassium channels (GIRKs). These channels are crucial for regulating cellular excitability and membrane potential in various tissues, including the heart, brain, and smooth muscle. The Kir2 family is comprised of four main subtypes: Kir2.1, Kir2.2, Kir2.3, and Kir2.4.

Inward rectification means that these channels conduct potassium ions more easily when the membrane potential is negative (inward current) than when it is positive (outward current). This property is due to the voltage-dependent block of the channel pore by intracellular polyamines and magnesium ions. When the membrane potential hyperpolarizes, these blocking ions are expelled from the pore, allowing potassium ions to flow out of the cell, thus tending to hyperpolarize the membrane further. Conversely, when the membrane depolarizes, these ions can enter the pore and block potassium efflux, limiting outward current.

Kir2 channels play significant roles in cardiac function, contributing to the resting membrane potential and action potential repolarization in cardiomyocytes. In neurons, they are involved in setting the resting membrane potential and influencing neuronal firing patterns. Mutations in Kir2 genes have been linked to various diseases, including cardiac arrhythmias like the Long QT syndrome (specifically LQT7, caused by Kir2.1 mutations) and neurological disorders. Their function is often modulated by G protein signaling, hence the alternative name GIRKs.