KCNJ3 and cardiac arrhythmia: In summary, alteration of miR-221 and -222 expression can contribute to changed L-type Ca2+ channel density, GIRK1/4 density, and, perhaps, Kir2.1 density resulting in slower excitation propagation and possibly disturbed electromechanical coupling, prolonging the QT interval, and thereby making the heart more vulnerable to arrhythmias.