KCNJ2 and atrial fibrillation: Because inward‐rectifier K+ (Kir) channels and voltage‐gated K+ (Kv) channels are considered to be important regulators of electrophysiology in AF,18 we measured the current density of Kir2.1 (a main member of the Kir2 subfamily) and Kv channels in isolated atrial myocytes.