Abstract 5326: S100A1 Prevents Arrhythmogenic Diastolic Sarcoplasmic Reticulum Calcium Leak In Ventricular Cardiomyocytes

Abstract

Background: S100A1 is an inotropic calcium (Ca) sensor protein in cardiomyocytes interacting with the cardiac ryanodine receptor (RyR2). Previous studies of our group have shown that S100A1 protein can decrease Ca spark frequency in permeabilized ventricular cardiomyocytes (CMs). We therefore hypothesized that S100A1 might prevent arrhythmogenic sarcoplasmic reticulum (SR) Ca leak in CMs. Methods and Results: Ventricular rat cardiomyocytes were enzymatically isolated and transfected either with 10 MOI of a CMV-GFP control or CMV-S100A1/CMV-GFP adenovirus resulting in GFP fluorescence in >99% of cultured GFP-CMs and S100A1-CMs as assessed by epifluorescent microscopy after 24-hours. Expression analysis revealed a 3-fold increase in S100A1 protein in S100A1-CM levels compared to GFP-CM. Confocal line-scan microscopy yielded a 50% reduction in Ca spark frequency in rhodamin2-AM loaded quiescent S100A1-CMs and epifluorescent imaging showed a 20% and 50% increase in the SR Ca content and systolic Ca transient amplitude, respectively, in FURA2-AM loaded 2Hz-stimulated S100A1-CM (37°C, 1.8 mM Ca) compared with GFP-CMs. Pathophysiological diastolic SR Ca leak was induced subjecting 2Hz-stimulated FURA2-AM loaded CMs to 0.5 mM caffeine and 10–7 M isoproterenol (caff/iso) as previously published by Isner and co-workers. As expected, this protocol resulted in permanent diastolic Ca waves in 100% (n=60/60) of 2Hz-stimulated iso/caff-treated GFP-CMs and was accompanied by significantly increased diastolic Ca levels and reduced systolic Ca transient amplitudes compared with iso-treated GFP-CMs. However, S100A1 efficiently protected more than 80% of iso/caff treated S100A1-CMs (n=49/60 cells, P<0.05 vs. iso/caff GFP-CMs) from diastolic Ca waves and further alterations of CM Ca handling. Importantly, similar results were obtained in caff/iso-treated failing rat GFP- and S100A1-CMs (data not shown). Conclusions: Here we show for the first time that S100A1 can both diminish the physiological SR Ca leak and protect from arrhythmogenic Ca waves in CMs. Given its beneficial effects in the context of experimental HF animal models, S100A1 therapeutic inotropic actions might be complemented by an antiarrhythmic effect targeting dysfunctional RyR2.