Murine Gap Junction Remodelling Induced By Subdiaphragmatic Pacing
File(s)
Author(s)
Kontogeorgis, Andrianos
Type
Thesis
Abstract
This thesis aims to adapt and develop a mouse model for stable dyssynchronous pacing and
systematic investigation of mechanisms of structural gap-junctional remodelling (GJR) and
correlation to functional changes. GJR, an altered abundance or localisation of connexin
proteins strongly correlates with arrhythmogenic substrates.
Wild type Cx43+/+ and heterozygous Cx43 knockout Cx43+/− (66% mean reduction in Cx43)
mice were paced in vivo subxiphisternally at 10-15% above anaesthetised sinus rates for one
to six hours avoiding intubation, vascular access, thoracic or mediastinal disruption.
In Cx43+/+ mice, pacing resulted in electrical and mechanical dyssynchrony.
Echocardiographic (ECHO) and electrocardiogram (ECG) indices, ventricular effective
refractory period (VERP) and arrhythmia inducibility were not significantly altered. Pacing
attenuated transmural gradients of Cx43 immunosignal in the LV free wall. Significant
reductions in Cx43 mRNA abundance at the LV free wall occurred. Cx43, its isoforms and
interacting protein expression were unchanged. Fractionation studies of 6hr-paced hearts
demonstrated reduced Cx43 in membrane fractions while cytosolic fractions increased
significantly. Cx43 degradation studies demonstrated substantially increased ubiquitinated
forms with pacing.
Cx43 protein expression in paced and unpaced Cx43+/− mice hearts was unchanged. In
contrast to Cx43+/+ cells, Cx43+/− mice demonstrated significantly shorter action potential
durations (APD), increased steady-state (Iss) and inward rectifier (IK1) potassium currents.
Pacing prolonged action potential duration (APD) at 50ms and 90ms increased VERP at
80ms/100ms and significantly reduced Iss in Cx43+/− vs. unpaced Cx43+/− hearts.
Pacing induces electro-mechanical dyssynchrony in wildtype Cx43 (Cx43+/+) hearts, results
in remodelling of the cardiac gap junctions without sustained measurable effects or increased
arrhythmia inducibility. Transgenic hearts (Cx43+/−) respond quite differently to pacing,
which may be relevant in cardiac disease, where Cx43 is focally reduced. Pacing could lead
to the remodelling of repolarisation currents in regions of reduced Cx43, enhancing
dispersion of refractoriness and potentially creating a substrate for arrhythmia re-entry.
systematic investigation of mechanisms of structural gap-junctional remodelling (GJR) and
correlation to functional changes. GJR, an altered abundance or localisation of connexin
proteins strongly correlates with arrhythmogenic substrates.
Wild type Cx43+/+ and heterozygous Cx43 knockout Cx43+/− (66% mean reduction in Cx43)
mice were paced in vivo subxiphisternally at 10-15% above anaesthetised sinus rates for one
to six hours avoiding intubation, vascular access, thoracic or mediastinal disruption.
In Cx43+/+ mice, pacing resulted in electrical and mechanical dyssynchrony.
Echocardiographic (ECHO) and electrocardiogram (ECG) indices, ventricular effective
refractory period (VERP) and arrhythmia inducibility were not significantly altered. Pacing
attenuated transmural gradients of Cx43 immunosignal in the LV free wall. Significant
reductions in Cx43 mRNA abundance at the LV free wall occurred. Cx43, its isoforms and
interacting protein expression were unchanged. Fractionation studies of 6hr-paced hearts
demonstrated reduced Cx43 in membrane fractions while cytosolic fractions increased
significantly. Cx43 degradation studies demonstrated substantially increased ubiquitinated
forms with pacing.
Cx43 protein expression in paced and unpaced Cx43+/− mice hearts was unchanged. In
contrast to Cx43+/+ cells, Cx43+/− mice demonstrated significantly shorter action potential
durations (APD), increased steady-state (Iss) and inward rectifier (IK1) potassium currents.
Pacing prolonged action potential duration (APD) at 50ms and 90ms increased VERP at
80ms/100ms and significantly reduced Iss in Cx43+/− vs. unpaced Cx43+/− hearts.
Pacing induces electro-mechanical dyssynchrony in wildtype Cx43 (Cx43+/+) hearts, results
in remodelling of the cardiac gap junctions without sustained measurable effects or increased
arrhythmia inducibility. Transgenic hearts (Cx43+/−) respond quite differently to pacing,
which may be relevant in cardiac disease, where Cx43 is focally reduced. Pacing could lead
to the remodelling of repolarisation currents in regions of reduced Cx43, enhancing
dispersion of refractoriness and potentially creating a substrate for arrhythmia re-entry.
Version
Open Access
Date Issued
2013-06
Date Awarded
2014-09
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Peters, Nicholas
Kaba, Riyaz
Sponsor
British Heart Foundation
National Institutes of Health (U.S.)
American Heart Association
Grant Number
RG/05/009
HL081336 / HL066140
Publisher Department
National Heart & Lung Institute
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)