Intercalated Disk Extracellular Nanodomain Expansion in Patients With Atrial Fibrillation.

Tristan B Raisch,Soufian T Almahameed,D Ryan King,Rengasayee Veeraraghavan,William S Arnold,Joseph W Baker,Matthew S Yanoff,Robert G Gourdie,Mohammed A Farooqui,Steven Poelzing,Timothy R Larsen

doi:10.3389/fphys.2018.00398

Tristan B Raisch, Soufian T Almahameed + Show 9 more

Open Access

https://doi.org/10.3389/fphys.2018.00398

Copy DOI

Abstract

Aims: Atrial fibrillation (AF) is the most common sustained arrhythmia. Previous evidence in animal models suggests that the gap junction (GJ) adjacent nanodomain – perinexus – is a site capable of independent intercellular communication via ephaptic transmission. Perinexal expansion is associated with slowed conduction and increased ventricular arrhythmias in animal models, but has not been studied in human tissue. The purpose of this study was to characterize the perinexus in humans and determine if perinexal expansion associates with AF.Methods: Atrial appendages from 39 patients (pts) undergoing cardiac surgery were fixed for immunofluorescence and transmission electron microscopy (TEM). Intercalated disk distribution of the cardiac sodium channel Nav1.5, its β1 subunit, and connexin43 (C×43) was determined by confocal immunofluorescence. Perinexal width (Wp) from TEM was manually segmented by two blinded observers using ImageJ software.Results: Nav1.5, β1, and C×43 are co-adjacent within intercalated disks of human atria, consistent with perinexal protein distributions in ventricular tissue of other species. TEM revealed that the GJ adjacent intermembrane separation in an individual perinexus does not change at distances greater than 30 nm from the GJ edge. Importantly, Wp is significantly wider in patients with a history of AF than in patients with no history of AF by approximately 3 nm, and Wp correlates with age (R = 0.7, p < 0.05).Conclusion: Human atrial myocytes have voltage-gated sodium channels in a dynamic intercellular cleft adjacent to GJs that is consistent with previous descriptions of the perinexus. Further, perinexal width is greater in patients with AF undergoing cardiac surgery than in those without.

Highlights

Atrial fibrillation (AF) is the most common cardiac arrhythmia affecting an estimated 5.2 million Americans (Colilla et al, 2013)
We have demonstrated in animal models (George et al, 2015, 2016, 2017; Veeraraghavan et al, 2015; Entz et al, 2016; Veeraraghavan and Gourdie, 2016) that altering perinexal width is associated with altered cardiac conduction consistent with the theories of ephaptic coupling (Kucera et al, 2002; Mori et al, 2008; Lin and Keener, 2010; Hichri et al, 2018)
Tissue was washed the following day, placed in phosphate buffered saline (PBS), and stored at 4◦C prior to transport to the Virginia-Maryland College of Veterinary Medicine for transmission electron microscopy (TEM) slide preparation and imaging. 46 patients were enrolled in the study, tissue was retrieved from 39 patients, 7 patient samples were not collected as cannulation occurred outside of the atria

Summary

Introduction

Atrial fibrillation (AF) is the most common cardiac arrhythmia affecting an estimated 5.2 million Americans (Colilla et al, 2013). A number of studies in animal models and humans have demonstrated that gap junction (GJ) remodeling is associated with abnormal atrial conduction and AF (Lübkemeier et al, 2013; Yan et al, 2013; Dhillon et al, 2014; Rothe et al, 2014). Recent studies suggest that GJs are not the only mechanism for electrical communication between cardiac myocytes. Our research suggests that ephaptic coupling, via the generation of electric fields and ion accumulation/depletion transients within restricted intercalated disk domains, can well describe a number of conduction abnormalities associated with GJ, sodium channel, and ionic modulation (Veeraraghavan et al, 2012, 2015, 2016; George et al, 2015, 2016, 2017; Entz et al, 2016)

Methods

Results

Discussion

Conclusion