Monitoring mitochondrial calcium and metabolism in the beating MCU-KO heart.

Optical methods for measuring intracellular ions including Ca(2+) revolutionized our understanding of signal transduction. However, these methods are not extensively applied to intact organs due to issues including inner filter effects, motion, and available probes. Mitochondrial Ca(2+) is postulated to regulate cell energetics and death pathways that are best studied in an intact organ. Here, we develop a method to optically measure mitochondrial Ca(2+) and demonstrate its validity for mitochondrial Ca(2+) and metabolism using hearts from wild-type mice and mice with germline knockout of the mitochondria calcium uniporter (MCU-KO). We previously reported that germline MCU-KO hearts do not show an impaired response to adrenergic stimulation. We find that these MCU-KO hearts do not take up Ca(2+), consistent with no alternative Ca(2+) uptake mechanisms in the absence of MCU. This approach can address the role of mitochondrial Ca(2+) to the myriad of functions attributed to alterations in mitochondrial Ca(2+).