Reduced Expression of the Cardiomyocyte GLUT4 Transporter is Associated with Cardiac Hypertrophy and Disturbances in Excitation–Contraction Coupling

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Abstracts

ABSTRACTS

525 Analysis of Dihydropyridine and Ryanodine Receptor Clusters in Healthy and Failing Human Cardiac Myocytes David Crossman 1,∗ , Christian Soeller 1 , Peter Ruygrok 2 , Mark Cannell 1 1 The

University of Auckland, Auckland, New Zealand; City Hospital, Auckland, New Zealand

2 Auckland

Excitation contraction coupling in cardiac ventricular muscle is regulated through calcium-induced calcium release (CICR). This process is where the action potential triggers the opening of voltage sensitive calcium channel or dyhyropyridine receptor (DHPR) on the plasma or t-tubular membrane of cardiac myocytes. This allows a small influx of Ca2+ (L-type current) into the cardiac cells which then induces the opening of the sarcoplasmic reticulum ryanodine receptor causing a much larger release of Ca2+ in the form of a calcium spark. Propagation of these sparks throughout the cell allows cytoplasmic build up of Ca2+ that in turn triggers muscle contraction. The close association of DHPR and RYR2 in a structure termed the dyad is critical to successful CICR. Several animal models of heart failure have demonstrated dyssynchronous Ca2+ release is associated with disrupted t-tubular network including a decrease in DHPR/RYR colocalisation. We hypothesised that similar disorganisation in myocyte architecture may be found in human heart failure and contribute to poor calcium signalling. To test this hypothesis diseased and normal human cardiac tissue obtained with informed consent was analysed in 3D. This involved fluorescently immunolabelling tissue for DHPR and RYR and imaging with a confocal microscope followed by 3D digital deconvolution to increase signal to noise ratio and enhance resolution. The results from this analysis will be presented and its implications for human heart failure discussed.

Heart, Lung and Circulation 2008;17S:S219–S241

excitation–contraction-coupling mechanisms in insulinresistant cardiomyopathy. Cardiac specific GLUT4 knock-out (GLUT4-KO) mice and their littermate controls which show a global GLUT4 knock-down (GLUT4-KD) were used for this study. We have previously reported that GLUT4-KO and GLUT4KD exhibit >95% and 85% reduction in GLUT4 expression respectively, relative to wild-type C57Bl6. Cardiomyocytes were isolated enzymatically from hearts of 15 to 35-week-old male mice. The GLUT4-KO mice exhibited significantly greater heart weight (380.5 ± 16.8 vs. 217 ± 6.0 mg, p < 0.001) and cardiac weight index (14.2 ± 0.6 vs. 7.8 ± 0.2 mg/g, p < 0.001) compared to GLUT4-KD mice. Myocyte Ca2+ currents and Na+ /Ca2+ exchanger currents were measured using whole cell patch clamp recording techniques, and normalized for myocyte size determined by capacitance measurement (pA/pF). Mean capacitance of GLUT4-KO myocytes was significantly greater than GLUT4-KD (437 ± 28 vs. 269 ± 15 pF, p < 0.0001). In GLUT4KO, peak voltage-activated (holding potential −90 mV) Ca2+ channel current density was significantly reduced compared with GLUT4-KD (−2.82 ± 0.3 vs. −5.33 ± 0.7 pA/pF, p < 0.05). The Ni-sensitive Na+ /Ca2+ exchange currents were significantly larger in the GLUT4-KO in both inward (−1.56 ± 0.29 vs. −0.83 ± 0.16 pA/pF, p < 0.05) and outward modes (1.82 ± 0.25 vs. 1.09 ± 0.1 pA/pF, p < 0.02). Thus, cardiac-specific knockout of the GLUT4 transporter results in significant cardiac hypertrophy and major alterations in cardiomoycyte Ca2+ homeostasis. Further exploration of this perturbation in Ca2+ flux is required. doi:10.1016/j.hlc.2008.05.580 527 Prevention of Cardiovascular Damage in Hypertensive Rats by Resveratrol Rebecca Vella ∗ , Candice Bowen, Andrew Fenning

doi:10.1016/j.hlc.2008.05.579

CQU, Rockhampton, QLD, Australia

526 Reduced Expression of the Cardiomyocyte GLUT4 Transporter is Associated with Cardiac Hypertrophy and Disturbances in Excitation–Contraction Coupling

Reactive oxygen species are implicated in the generation of inflammation, decrease of vascular and tissue nitric oxide (NO) concentrations and damage to the cardiovascular system following hypertension. The aim of this study was to examine the antioxidant, antiinflammatory and cardio-protective effects of resveratrol (R) (2 mg/(kg day) for 8 weeks) in 2-month-old spontaneously hypertensive rats (SHR). The WKY rat was used as the control. Rats were divided into WKY, WKY + R, SHR and SHR + R treated groups. SHR rats developed hypertension (WKY 150.7 ± 4.8; SHR 195.6 ± 6.3*), increased heart rates, decreased developed pressures (WKY 118 ± 6; SHR 58 ± 6*), and rates of contraction, decreased vascular responses to noradrenaline (NA), acetylcholine (ACh) and sodium nitroprusside (NaN), increased left ventricular mass and serum concentrations of MDA (WKY 57.8 ± 6.8; SHR 91.7 ± 11.8*), and TNF␣ with a decrease in NO concentrations (WKY 2.2 ± 0.2; SHR 1.5 ± 0.3*). Hypertension did not induce changes in cardiac stiffness or circulating

Vennetia Danes 1,∗ , Vennetia Danes 2 , Claire Curl 1 , Jenny Favaloro 1 , Joseph Proietto 1 , Lea Delbridge 1 1 University

of Melbourne, Melbourne, Victoria, Australia; Ratulangi University, Manando, North Sulawesi Province, Indonesia

2 Sam

Impaired myocardial glut4-mediated glucose uptake is associated with cardiac hypertrophy and contractile dysfunction. The cellular mechanisms that underlie these pathologies, specifically the disturbances in ionic homeostasis relating to excitation–contraction coupling have yet to be clarified. In this study we used a cre-lox GLUT4-deficient murine model to investigate changes in