TNFα Modulates Cardiac Conduction by Altering Electrical Coupling between Myocytes

Abstract

Background: Tumor Necrosis Factor α (TNFα) upregulation during acute inflammatory response has been associated with numerous cardiac effects including modulating Connexin43 and vascular permeability. This may in turn alter cardiac gap junctional (GJ) coupling and extracellular volume (ephaptic coupling) respectively. We hypothesized that acute exposure to pathophysiological TNFα levels can modulate conduction velocity (CV) in the heart by altering electrical coupling: GJ and ephaptic.Methods and Results: Hearts were optically mapped to determine CV from control, TNFα and TNFα + high calcium (2.5 vs. 1.25 mM) treated guinea pig hearts over 90 mins. Transmission electron microscopy was performed to measure changes in intercellular separation in the gap junction-adjacent extracellular nanodomain—perinexus (WP). Cx43 expression and phosphorylation were determined by Western blotting and Cx43 distribution by confocal immunofluorescence. At 90 mins, longitudinal and transverse CV (CVL and CVT, respectively) increased with control Tyrode perfusion but TNFα slowed CVT alone relative to control and anisotropy of conduction increased, but not significantly. TNFα increased WP relative to control at 90 mins, without significantly changing GJ coupling. Increasing extracellular calcium after 30 mins of just TNFα exposure increased CVT within 15 mins. TNFα + high calcium also restored CVT at 90 mins and reduced WP to control values. Interestingly, TNFα + high calcium also improved GJ coupling at 90 mins, which along with reduced WP may have contributed to increasing CV.Conclusions: Elevating extracellular calcium during acute TNFα exposure reduces perinexal expansion, increases ephaptic, and GJ coupling, improves CV and may be a novel method for preventing inflammation induced CV slowing.

Intercalated Disk Extracellular Nanodomain Expansion in Patients With Atrial Fibrillation

“…This nanodomain, termed the “perinexus,” is an extracellular space in the intercalated disk directly adjacent to GJ plaques that is narrow (on the scale of 5–30 nm), can be dynamically altered, and contains a high density of the cardiac isoform of the voltage gated sodium channel ( Rhett et al, 2012 ; Veeraraghavan et al, 2015 , 2016 ; Veeraraghavan and Gourdie, 2016 ). Furthermore, 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 ). While evidence has grown suggesting the importance of non-gap junctional coupling mediating conduction velocity in animal models, it is unknown whether the perinexus can be found in human myocardium, and more specifically the atria.…”

“…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 ).…”

“…Previously, we reported that perinexal separation in guinea pig ventricular myocardium is approximately 12 nm ( Veeraraghavan et al, 2015 ). We later found with different observers that perinexal separation can vary between 10 and 25 nm depending on the ex vivo perfusate used to sustain the heart through studies ( George et al, 2015 , 2016 , 2017 ; Entz et al, 2016 ; Greer-Short et al, 2017 ).…”

The Role of Cardiac Macrophage and Cytokines on Ventricular Arrhythmias

“…CV is determined by the ion channel and cellular interconnections. George et al (2017) demonstrated that TNFα could reduce CV by altering electrical coupling between myocytes in guinea pig hearts. The effects of TNF-α on gap junction coupling have been extensively studied.…”

“…The effects of TNF-α on gap junction coupling have been extensively studied. TNF-α alters Cx43 expression, reduces Cx43 phosphorylation, and alters Cx43 redistribution, which is important in modulating Cx43 channel conductance (Fernandez-Cobo et al, 1999;Sawaya et al, 2007;George et al, 2017).…”