Altered Calcium Handling Is Critically Involved in the Cardiotoxic Effects of Chronic β-Adrenergic Stimulation

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Abstract
Background— Chronic adrenergic stimulation leads to cardiac hypertrophy and heart failure in experimental models and contributes to the progression of heart failure in humans. The pathways mediating the detrimental effects of chronic β-adrenergic stimulation are only partly understood. We investigated whether genetic modification of calcium handling through deletion of phospholamban in mice would affect the development of heart failure in mice with transgenic overexpression of the β 1 -adrenergic receptor. Methods and Results— We crossed β 1 -adrenergic receptor transgenic (β 1 TG) mice with mice homozygous for a targeted deletion of the phospholamban gene (PLB −/− ). Phospholamban ablation dramatically enhanced survival of β 1 TG mice. The decrease of left ventricular contractility typically observed in β 1 TG mice was reverted back to normal by phospholamban ablation. Cardiac hypertrophy and fibrosis were significantly inhibited in β 1 TG/PLB −/− mice compared with β 1 TG mice, and the heart failure–specific gene expression pattern was normalized. Analysis of intracellular calcium transients revealed increased diastolic calcium levels and decreased rate constants of diastolic calcium decline in β 1 TG mice. In β 1 TG/PLB −/− mice, diastolic calcium concentration was normal and rate constants of diastolic calcium decline were greater than in wild-type mice. Conclusions— We conclude that modification of abnormal calcium handling in β 1 TG mice through ablation of phospholamban resulted in a rescue of functional, morphological, and molecular characteristics of heart failure in β 1 -adrenergic receptor–transgenic mice. These results imply altered calcium handling as critical for the detrimental effects of β 1 -adrenergic signaling.