The small EF-hand Ca²⁺ binding protein S100A1 increases contractility and Ca²⁺ cycling in rat cardiac myocytes

Abstract

S100A1 is an interesting Ca²⁺ binding protein with respect to muscle physiology as it is preferentially expressed in cardiac muscle and colocalizes with the sarcolemmal and the sarcoplasmic reticulum membranes as well as with the sarcomere. It is therefore conceivable that S100A1 may play a specific role in the regulation of cardiac Ca²⁺ homeostasis and contractility. We therefore investigated the impact of adenoviral S100A1 overexpression on fractional shortening (FS%) and systolic Ca²⁺ transients in adult rat cardiomyocytes as well as of S100A1 protein on SERCA activity in skinned cell preparation. In our setting S100A1 gene transfer increased FS% by 55 %, systolic Ca²⁺ amplitudes by 62 %, while S100A1 protein increased SERCA activity by 28 %. Importantly, the gain in systolic Ca²⁺ supply was not only seen on basal conditions but also with isoproterenol-stimulated Ca²⁺ cycling. Thus, S100A1 enhances cardiac contractility by increasing intracellular Ca²⁺ fluxes at least in part due to a modulation of SERCA. Since earlier observations demonstrated S100A1 protein levels to be increased in compensatory hypertrophy and significantly downregulated in end stage heart failure, these functional data suggest that S100A1 is a novel determinant of cardiac function whose expression levels are causally related to the prevailing contractile state of the heart.