Assessment of Cardiac Function of Rbm 20−/− Rats Using Pressure‐Volume Loop Analysis After 28 Days of Angiotensin II Treatment

Abstract

RNA binding motif 20 (Rbm20), a muscle specific splicing factor for the sarcomeric protein titin, affects diastolic and systolic properties of the heart per the Frank‐Starling mechanism. Failure to alter titin expression from the predominant fetal isoform N2BA to the shorter, adult N2B isoform in Rbm20−/− (KO) rats, results in impaired cardiomyocyte relaxation, increased compliance of the ventricular walls, and dilated cardiomyopathy. These pathologies are similar to those seen in humans with this mutation, which often results in early, sudden death in both species. Angiotensin II (AII) acutely causes vasoconstriction, and chronically results in cardiac hypertrophy, characterized by an increase in cardiac wall stiffness. We hypothesized that 28 days of treatment with AII would increase the stiffness of the myocardium, resulting in improved cardiac function in KO rats. KO rats and age‐matched wild type (WT) controls were fitted with subdermal osmotic pumps, delivering AII continuously (0.25 μL·hr −1) for 28 days. After AII exposure, cardiac function was assessed in vivo using pressure‐volume loop analysis. Under isoflurane anesthesia, loops were recorded under baseline, brief inferior vena cava occlusion, and hypertonic saline infusion (20–40 μL) conditions. The rat was then heparinized, and blood collected for cuvette calibration. No group differences (p<0.05) were found in cardiac output (23.3±0.8 KO; 26.9±2.5 mL·min−1 WT), heart rate (295±21 KO; 341±16 b·min−1 WT), and stroke volume (80.8±9.1 KO; 79.5±7.6 μL WT). However, significant reductions were found in contractility (preload recruitable stroke work; 41.6±10.8 KO; 86.9±8.2 mmHg WT), stroke work (5.13±0.73; 8.13±0.86 mmHg·min WT), and ejection fraction (49.8±4.2 KO; 74.7±7.4 % WT) in KO rats. KO rats were able to maintain stroke volume, despite impaired contractility, due to a significant increase in preload (169±16 KO; 113±7 μL WT) and decrease in afterload (84.4±8.7 KO; 113±9 mmHg WT). We conclude that KO rats failed to improve contractility with 28 days of AII treatment, but maintained normal cardiac output through compensatory changes in preload and afterload.Support or Funding InformationThis project is supported in part by a grant from the National Institute of General Medical Sciences (2P20GM103432) from the National Institutes of Health. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.