Dominant-negative suppression of IK1 in the mouse heart leads to altered cardiac excitability

The inward rectifier potassium current in the heart, IK1, has been suggested to play a significant role in cardiac excitability by contributing to the late phase of action potential (AP) repolarization and the stabilization of resting potential. To further assess the role of IK1 in cardiac excitability we have produced transgenic mice expressing a dominant-negative subunit of the Kir2.1 channel, a major molecular determinant of IK1 in the heart, and studied the effects of IK1 suppression on major potassium currents, APs and the overall electrical activity of the heart. Kir2.1 channel subunits with a mutated signature sequence (AAA for GYG substitution) were expressed in the heart under control of the α-myosin heavy chain promoter. Two lines of transgenic mice were established, both expressing high levels of Kir2.1-AAA-GFP (GFP, green fluorescent protein) subunits in all major parts of the heart. In ventricular myocytes isolated from transgenic mice, IK1 was reduced by 95% in both lines, leading to a significant prolongation of APs. Surface ECG recordings from anesthetized transgenic mice revealed significant changes in key parameters of excitability, including prolongation of QRS complexes and QT intervals. This study confirms the significant role of IK1 in control of AP repolarization and major ECG intervals in the intact heart.