Introduction:
The underlying mechanisms contributing to uremic cardiomyopathy during chronic kidney disease (CKD) are poorly understood, limiting treatment options.
Hypothesis:
We aimed to determine if altered calcium (Ca2+) handling in cardiomyocytes contributes to diastolic dysfunction in a mouse model of CKD.
Methods:
CKD was induced in male 129X1/SvJ mice through five-sixths nephrectomy in a two-stage surgery. Age-matched mice served as controls. Transthoracic echocardiography and speckle-tracking based strain analysis (Vevo2100, VisualSonics, Toronto, Canada) were performed at 8 weeks post-CKD (n=7-8) to assess heart structure and function. Cardiomyocytes isolated from mice with or without CKD (n=3 mice per group, 10-12 cells/mouse) were loaded with Fura 2-AM, paced by field stimulation (1 Hz), and imaged with a dual-excitation fluorescence photomultiplier system (IonOptix Inc, Milton, MA) to measure Ca2+ transients and sarcomere length. Sarcoplasmic reticulum Ca2+ content was determined following rapid application of caffeine.[[Unable to Display Character: 
]]
Results:
CKD mice displayed left ventricular hypertrophy (LVAW;d 1.46 ± 0.134 vs 1.04 ± 0.129 mm; p<0.001) and decreased longitudinal strain (19 ± 4.1% vs 30 ± 2.3%; p<0.0001) compared to control mice. Resting sarcomere length was significantly shorter in cardiomyocytes isolated from CKD mice compared to normal mice (1.86 ± 0.054 vs 1.89 ± 0.047 nm; p = 0.016), but relaxation time was unchanged (0.21 ± 0.12 vs 0.21 ± 0.15 seconds, p=0.4). Unexpectedly, the baseline cytosolic Ca2+ content was lower in uremic myocytes (1.22 ± 0.353 vs 1.46 ± 0.252 AU, p=0.002). However, the Ca2+ transient amplitude (0.39 ± 0.177 vs 0.41 ± 0.167 AU, p=0.4) and sarcoplasmic reticulum Ca2+ content (1.15 ± 0.321 vs 1.24 ± 0.550 AU, p=0.4) were comparable between CKD and normal cardiomyocytes.[[Unable to Display Character: 
]]
Conclusions:
Mice with CKD have signs of left ventricular hypertrophy and diastolic dysfunction on echocardiography. Cardiomyocytes isolated from mice with CKD have shorter diastolic sarcomere length implying impaired relaxation, yet paradoxically have decreased diastolic calcium. Thus Ca2+ accumulation during diastole does not appear to contribute to impaired relaxation in this model.
INSIGHTS INTO DIASTOLIC DYSFUNCTION IN PATIENTS WITH LEFT VENTRICULAR HYPERTROPHY AND T-WAVE INVERSION ON THE 12-LEAD ELECTROCARDIOGRAM