Decreased SERCA pump expression and activity have been implicated in diastolic dysfunction and heart failure. To better define the role of decreased SERCA pump expression we developed a SERCA2 gene knockout (-/+) model. However, heterozygous mice (born with only a single functional allele of the SERCA2 gene) induce several compensatory alterations in expression and activity of other Ca2+ handling proteins to make up a decrease in SERCA pump function. Thus, a chronic reduction in SERCA2 activity results in a new equilibrium set point for the regulation of cardiomyocyte Ca2+ homeostasis. To overcome this problem we will develop a Conditional knockout (cKO) mouse model to ablate the SERCA2 gene in a heart specific and inducible manner in adult stages. Studies also indicate that SERCA2a and 2b are co-expressed in the heart and SERCA2b can substitute for SERCA2a function. Compared with SERCA2a, SERCA2b has 49 extra C-terminal amino acids and has a higher Ca2+ affinity and lower turnover rate. We hypothesize that SERCA2b plays a unique role in SR Ca2+ uptake (because of its high apparent affinity for Ca2+ ion) and is important for maintaining low cytosolic Ca2+ content. To define the role of SERCA2b we will use adenoviral-mediated SERCA gene transfer into adult rat myocytes. In addition, we have preliminary data to suggest that SERCA protein either forms a complex or co-localizes with its regulatory molecules (PLB, sarcolipin, PKA, CaMKII, Phosphatase 1 and 2a, tethered via anchoring molecules) for efficient regulation of SR Ca2+ uptake function. In this proposal we seek to identify the SERCA macromolecular complex using immuno-precipitations and 2D gel analyses and MASS spectrometry. Collectively, these studies will allow us to better understand the role of SERCA2a and 2b pumps in the beat-to-beat function of the myocardium. As such, these studies are likely to suggest novel clinical strategies that might be pursued for the management of chronic heart failure in humans. ? ?
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