MiPsummer Programme pdf - Mitochondrial Physiology Society

57
Time dependence of diet-induced conduction disturbances in the heart
Abstract # 28
Christa Funch Jensen 1 , Lasse Skibsbye 1 , Emil Daniel Bartels 2 , Lars Bo Nielsen 2 , Niels-Henrik Holstein-
Rathlou 1 , Thomas Jespersen 1 , Morten Schak Nielsen 1 , and Lene Nygaard Axelsen 1
1 Department of Biomedical Sciences and The Danish National Research Foundation Centre for Cardiac
Arrhythmia, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark; 2 Department of
Clinical Biochemistry, Copenhagen University Hospital Rigshospitalet, Copenhagen, Denmark
E-mail: christafjen@sund.ku.dk
Background: Diabetes and metabolic syndrome causes cardiac complications, including electrical
abnormalities that increase the risk for cardiac arrhythmias and sudden death. The pathogenesis, however,
remains unknown. We have previously established fructose and fat fed rats (FFFRs) as a pre-diabetic model,
which within 6 weeks of feeding exhibit intramyocardial lipid accumulation, decreased cardiac conduction
velocity (CV), and increased risk of ventricular fibrillation following ischemia-reperfusion. The CV slowing
is not explained by Na + -channel, K + -channel or gap junction conductance levels or kinetics, however, CV
may be altered by a depolarized resting membrane potential resulting in decreased Na + channel availability.
Furthermore, acute cardiac lipid loading does not reduce CV per se, but changes in cardiac lipid profile may
contribute to CV slowing over time. Therefore, the aim of this study is to investigate the time dependence of
1) diet-induced cardiac CV disturbances and 2) changes in resting membrane potential and action potential
(AP) morphology.
Methods: Age-matched male Sprague-Dawley rats are divided into 2 groups. One group is fed unlimited
normal chow and the other a special diet consisting of 60 % fat in the chow and 10 % fructose in the drinking
water. Following 1, 3 and 6 weeks of feeding, cardiac CV, AP morphology as well as lipid content is
determined.
CV is measured by placing a ventricular tissue strip in a fluid chamber. A stimulation electrode is placed
on the apex end, propagating an impulse from apex to base. Two measuring electrodes are placed in series on
a muscle fiber bundle, and the conduction delay is determined. CV is thus calculated as the interelectrode
distance divided by the impulse delay.
Another ventricular tissue strip is placed in a separate fluid chamber, for resting membrane potential and
AP morphology characterization. A bipolar silver electrode is used for tissue stimulation and APs are
recorded with standard intracellular microelectrodes.
Ventricular triglyceride levels are quantified by thin layer chromatography following lipid extraction.
Lipid droplet volume percentage and intracellular localization are determined by confocal microscopy
subsequent to BODIPY staining.
Results: Preliminary data indicate that CV slowing occurs in FFFRs somewhere between 3 and 6 weeks of
feeding, which indicate that diet-induced CV disturbances takes relatively long time to develop. The results
on resting membrane potential and AP morphology are pending.