Two-Pore K+ Channel TREK-1 Regulates Sinoatrial Node Membrane Excitability

Two-pore K(+) channels have emerged as potential targets to selectively regulate cardiac cell membrane excitability; however, lack of specific inhibitors and relevant animal models has impeded the effort to understand the role of 2-pore K(+) channels in the heart and their potential as a therapeutic target. The objective of this study was to determine the role of mechanosensitive 2-pore K(+) channel family member TREK-1 in control of cardiac excitability.

Cardiac-specific TREK-1-deficient mice (αMHC-Kcnk(f/f)) were generated and found to have a prevalent sinoatrial phenotype characterized by bradycardia with frequent episodes of sinus pause following stress. Action potential measurements from isolated αMHC-Kcnk2(f/f) sinoatrial node cells demonstrated decreased background K(+) current and abnormal sinoatrial cell membrane excitability. To identify novel pathways for regulating TREK-1 activity and sinoatrial node excitability, mice expressing a truncated allele of the TREK-1-associated cytoskeletal protein βIV-spectrin (qv(4J) mice) were analyzed and found to display defects in cell electrophysiology as well as loss of normal TREK-1 membrane localization. Finally, the βIV-spectrin/TREK-1 complex was found to be downregulated in the right atrium from a canine model of sinoatrial node dysfunction and in human cardiac disease.

These findings identify a TREK-1-dependent pathway essential for normal sinoatrial node cell excitability that serves as a potential target for selectively regulating sinoatrial node cell function.