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Doctor of Philosophy (PhD)




In order to determine if mutations made to phospholemman (PLM) could increase PLM binding to the Na/K-ATPase (NKA) and cause positive inotropy we performed scanning mutagenesis of the transmembrane domain of PLM and measured FRET between each mutant and NKA. We observed increased binding to NKA for several PLM mutants compared to WT, including L27A, L30A, and I32A. In isolated cardiomyocytes, overexpression of WT PLM increased the amplitude of the Ca2+ transient compared to GFP control. Ca2+ transient amplitude was further increased by L30A PLM overexpression. L30A mutation also delayed Ca2+ extrusion and increased the duration of the cardiomyocyte contraction. This mimics aspects of the effect of cardiac glycosides, which are known to increase contractility through inhibition of NKA. No significant differences between WT and L30A PLM overexpression were observed after treatment with isoproterenol, suggesting that the effects of L30A are reversible with β-adrenergic stimulation. The results implicate L30 as an important functional determinant and suggest that expression of L30A PLM could increase cardiac contractility while providing physiological reversibility of NKA inhibition.

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