Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC25
IP3R expression is increased in a minimally invasive surgical mouse model of cardiac hypertrophy
T. Martin1, T. S. Chong1, M. MacDonald1, S. Currie1
1. University of Strathclyde, Glasgow, United Kingdom.
Cardiac hypertrophy is an adaptation to cardiac insult and can be used as an accurate predictor for development of heart failure. Abnormal calcium handling is a key process contributing to compromised cardiac function during cardiac hypertrophy. It is unclear whether the inositol-1,4,5-trisphosphate receptor type 2 (IP3R2) calcium release channel plays a role in the cardiac dysfunction that accompanies hypertrophy. Using a minimally invasive surgical model of transverse aortic banding (MTAB), IP3R2 protein expression was assessed in ventricular tissue from sham-operated and MTAB animals. Mice (20-25g, adult C57) were anaesthetised with 3% isofluorane and maintained on 1% isofluorane, both in 100% oxygen. Aortic arch ligation was performed without entering the pleural space (minimally invasive). A 27G needle was used to control the tightness of the band. Sham animals underwent the same procedure except the arch was not ligated. Contractile function was measured by echocardiography 14 days and 28 days after surgery. Left ventricular (LV) wall thickness (anterior wall and posterior wall thickness) and internal dimensions during diastole and systole (LVEDD/LVESD) were measured. LV fractional shortening, relative wall thickness and LV mass were calculated from short-axis view M-mode measurements. After hemodynamic recordings were completed, the hearts were rapidly excised following pentobarbital sodium overdose (intraperitoneal, 10 μl/g). Ventricular tissue was homogenized for quantitative western blotting or processed for histology. MTAB animals developed severe hypertrophy by week 4 as assessed by a significant increase in heart weight to body weight ratio (5.25±0.33 v’s 8.83±0.58, p=0.000, sham, n=7 v’s MTAB, n=11 respectively) with a 1.7-fold increase in LV mass in the mouse heart. Fractional shortening was decreased by 50.5% (49.00±3.34 v’s 24.78±2.44, p=0.001, sham, n=6 v’s MTAB, n=9 respectively) by week 4. Evidence for fibrosis was indicated by significantly increased collagen deposition as assessed by pico-sirius red staining (0.55±0.2 v’s 5.9±1.6, p=0.03, sham, n=4 v’s MTAB, n=6 respectively). IP3R2 protein expression (normalised to GAPDH) increased by approximately 2.9 fold in hearts from MTAB mice in comparison to sham (IP3R2:GAPDH ratio: 0.378±0.06 v’s 1.303±0.03, p=0.002, sham, n=7 v’s MTAB, n=11 respectively). There was a significant correlation between the gradient of slopes of IP3R2:GAPDH ratio and fractional shortening, where a decreased fractional shortening correlated with an increased IP3R2 expression (p<0.05, Spearman r= -0.73, n=13). In summary, there is a significant elevation in ventricular IP3R2 protein expression following pressure-overload -induced cardiac hypertrophy. A strong correlation exists between increasing IP3R2 protein levels and progression of cardiac dysfunction. Further investigations will explore the mechanistic contribution of altered channel expression to cardiac function.
Where applicable, experiments conform with Society ethical requirements