Inward rectifier potassium channel Kir2.1 (Kir2.1)

The inward rectifier potassium channel Kir2.1 is a member of the classical inwardly rectifying potassium channels encoded by the KCNJ2 gene. It forms a tetrameric ion-conducting pore that allows potassium ions (K⁺) to move more easily into cells than out, a property termed "inward rectification." This feature arises because intracellular polyamines and magnesium block outward current at depolarized potentials while permitting inward flow at hyperpolarized potentials. Kir2.1 plays an essential role in maintaining the resting membrane potential across excitable cell membranes—especially in cardiac myocytes and neurons—thereby stabilizing electrical activity required for normal heart rhythm, muscle contraction, neuronal signaling, insulin secretion from pancreatic beta cells, and overall electrolyte homeostasis. Structurally, each subunit contains two transmembrane helices flanking an extracellular selectivity filter with cytoplasmic N-terminal and C-terminal domains that contribute regulatory sites for lipids like PIP₂ as well as protein-protein interactions. The functional tetramer forms a central pore selective for K⁺. Genetic defects in KCNJ2 cause diseases such as Andersen-Tawil syndrome—characterized by periodic paralysis, ventricular arrhythmias, and dysmorphic features—and have also been linked to short QT syndrome due to altered repolarization dynamics. In research contexts—including neurogenetics—the overexpression or manipulation of Kir2.1 is used experimentally to hyperpolarize cells or modulate their excitability; its trafficking sequence has also been adapted for optogenetic tools like eNpHR3.0. No approved drugs specifically target Kir2.1 clinically; however experimental blockers such as barium are commonly used tools in electrophysiological studies, while genetic testing identifies pathogenic variants relevant to inherited disease diagnosis. Overall, Kir2.1 represents a critical molecular determinant of cellular excitability with major implications for cardiovascular health—and dysfunction when mutated—making it both a fundamental physiological regulator and an important disease-associated ion channel target.

Other names

KCNJ2 (gene name)IRK1Potassium inward rectifier 2.1IK1 channel (in cardiac context)

For blockers such as barium and cesium, the mechanism is direct pore blockade, preventing potassium ion flow through the channel at specific voltages by physically occluding the conduction pathway.