The mitochondrial calcium uniporter in the heart: energetics and beyond

Ca2+ and mitochondria are inextricably linked to cardiac function and dysfunction. Ca2+ is central to cardiac excitation-contraction coupling and stimulates mitochondrial energy production to fuel contraction. Under pathological conditions of dysregulated Ca2+ cycling, mitochondrial Ca2+ overload activates cellular death pathways. Thus, in the cardiomyocyte, the mitochondrial Ca2+ microdomain is where contraction, energy and death collide. A key component of mitochondrial Ca2+ signalling is the mitochondrial Ca2+ uniporter complex (uniplex), an inner membrane Ca2+ transporter and major pathway of mitochondrial Ca2+ entry. Once known only as the unidentified target for ruthenium red and related compounds, in recent years, the uniplex has evolved into a complex multiprotein assembly. The identification of the molecular constituents of the uniplex has made possible the generation of targeted genetic models to interrogate uniplex function in vivo. This review will summarize our current understanding of the molecular structure of the uniplex, its impact on mitochondrial energetics and cardiac physiology, its contribution to cardiomyocyte death, and its expanding roles in cardiac biology.