Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC26
Atrial IP3 receptor expression is increased in patients with left ventricular systolic dysfunction
T. Chong1, A. J. Workman2, A. C. Rankin2, S. Currie1
1. University of Strathclyde, Glasgow, United Kingdom. 2. University of Glasgow, Glasgow, United Kingdom.
Introduction: The arrhythmogenic mechanisms of atrial fibrillation (AF) are poorly understood, but likely involve a contribution from a pathological remodelling of atrial intracellular Ca2+-handling proteins. One candidate, highly expressed in human atrium, is the inositol 1,4,5-trisphosphate receptor (IP3R). It is unknown whether heart failure or left ventricular systolic dysfunction (LVSD), major causes of AF and atrial remodelling, also affect the expression of human atrial IP3R. Aims: To compare atrial IP3R protein expression levels between patients with and without LVSD, and to investigate correlations between IP3R expression and the LV ejection fraction (LVEF). Methods: Right atrial appendage tissues were obtained from 20 consenting patients with or without LVSD, who were in sinus rhythm and undergoing cardiac surgery. Tissues were homogenised and stored at -80 °C. After randomisation and blinding of homogenates, IP3R2 levels were quantified by western blotting using anti-IP3R type 2 antiserum and GAPDH as an internal control. To ensure that the protein load of homogenates was in the linear range of the densitometer, a pre-determined range of protein concentrations was tested, and protein loads of 6, 9 and 12 µg were selected. IP3R2:GAPDH ratios were obtained at each protein load, and the slope of the three IP3R2:GAPDH ratios was calculated for each sample. The mid-range (9 µg) load was also evaluated alone for comparison. Results: Patients with moderate or severe LVSD had a significantly higher atrial IP3R2:GAPDH ratio (9 µg protein load) than those with no LVSD (3.97±0.47, n=10 patients versus 2.54±0.13, n=10 patients; p<0.05, unpaired 2-tailed Student’s t-test with Welch’s correction). There was a correspondingly higher gradient of the slope of IP3R2:GAPDH ratios (6-12 µg protein load) in patients with moderate or severe LVSD than in those with no LVSD (0.33±0.02 versus 0.20±0.01, p<0.001). Furthermore, in the patient cohort as a whole, there was a significant correlation between the patients’ LVEF value (where available) and the IP3R2:GAPDH ratio (9 µg protein load), such that a decreasing LVEF correlated with increasing expression of IP3R2 (p<0.05, Spearman r= -0.70, n=9 patients). Conclusions: In patients in sinus rhythm and undergoing cardiac surgery, an increased expression of the atrial Ca2+-handling protein IP3R2 was independently associated with worsening LV systolic function. Such increased IP3 receptor expression might have the potential to contribute to the predisposition to AF in patients with LVSD or heart failure.
Where applicable, experiments conform with Society ethical requirements