Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC17
The effect of a non-obesogenic high-fat diet on excitation-contraction coupling in cardiomyocytes
B. Littlejohns1, H. Lin1, G. Angelini1, M. Suleiman1
1. Univeristy of Bristol, Bristol, United Kingdom.
High-fat diet can trigger cardiomyopathies that are normally associated with obesity-induced co-morbidities (e.g. diabetes, hypertension). However, high-fat diet can also directly trigger cardiac changes without obesity, by altering cardiac metabolism/function. The aim of this work was to investigate the effects of high-fat diet, pre-obesity and associated co-morbidities, on cardiomyocyte contractility and calcium cycling. Male C57BL/6 mice were fed either a normal rodent diet (13% kcal from fat) or a high-fat diet (45% kcal from fat and 0.15% cholesterol) for 24 weeks. Cardiomyocytes were isolated using a perfusion protocol which contained collagenase type-1 and protease to digest the heart. The isolated cells were then perfused with a HEPES buffer (pH 7.4). Ca2+ transients were measured using the ratiometric Fura-2 AM dye and the contraction was monitored using an edge tracking device. Data are presented as mean±SEM and analysed using ANOVA with Fisher’s PLSD post-hoc test. Feeding male C57BL/6 mice a high-fat diet for 24 weeks elevated blood cholesterol (148±10 to 214±11mg/dl, n=18-25/group) and triglycerides (79±16 to 187±14mg/dl, n=18-25/group) but had little effect on body weight (31.77±0.31 vs. 32.37±0.43g, n>50/group) and did not change blood glucose (135±25 vs. 136±7mg/dl, n=18-25/group). Percentage of twitch contraction (stimulated at 0.2Hz) increased from 7.2±0.3% in the normal diet to 12.7±0.3% in the high-fat diet, P<0.0001 (n=23-41 cells/group from 4-6 hearts/group). However, the amplitude of the Ca2+ transient was not different between the normal and high-fat diets (139±3% vs. 136±5%, P>0.05, n=19-32 cells/group from 2-4 hearts/group). This effect was also seen at different stimulation frequencies (0.5, 1.0 and 2.0Hz). In each frequency tested the time to peak contraction was significantly quicker in the high-fat group compared to the normal diet group, P<0.05. This did not correspond to a faster time to peak of the Ca2+ transient in high-fat diet compared to normal diet, P>0.05, except at 0.2Hz, P<0.05. These data show that isolated cardiomyocytes from mice fed a high-fat diet had a decreased time to peak shortening and increased amplitude of shortening during contraction compared to normal diet cardiomyocytes, which did not correlate with a faster time to peak and greater amplitude of the Ca2+ transient respectively. This contractility modification by high-fat diet could be attributed to increased myofilament sensitivity to Ca2+, or a change in the viscoelastic properties of the cardiomyocytes. Modifications to contractility and Ca2+ handling could have implications in the increased vulnerability to ischaemia-reperfusion in the high-fat group, either through Ca2+ overload and mitochondrial permeability transition pore opening or changes in ATP usage.
Where applicable, experiments conform with Society ethical requirements