Mitochondrial localization of NCXs: Balancing calcium and energy homeostasis.

It is well established that mitochondria are the main source of ATP production within cells. However, mitochondria have other remarkable functions, serving as important modulators of cellular Ca signaling, and it is now generally recognized that control over Ca homeostasis is intrinsically interwoven with mitochondrial abilities to adjust and tune ATP production. In this review, we describe the mechanisms that mitochondria use to balance Ca homeostasis maintenance and cell energy metabolism. In recent years, the knowledge on the molecular machinery mediating Ca influx/efflux has been improved and, albeit still open to further investigations, several lines of evidence converge on the hypothesis that plasma membrane Na/Ca exchanger (NCX) isoforms are also expressed at the mitochondrial level, where they contribute to the Ca and Na homeostasis maintenance. In particular, the connection between mitochondrial NCX activity and metabolic substrates utilization is further discussed here. We also briefly focus on the alterations of both mitochondrial Ca handling and cellular bioenergetics in neurodegenerative diseases, such as Parkinson's and Alzheimer's disease.