Targeting of reporter molecules to mitochondria to measure calcium, ATP, and pH.

The study of isolated mitochondria, dating back to the 60ties, has provided a wealth of information on the biochemical routes allowing these organelles, deriving from the adaptation of primordial symbionts, to couple oxidation of substrates to the production of ATP. In this work, concepts were acquired (such as, to name a few, the chemiosmotic mechanism of energy conservation, the import into mitochondria of most organelle proteins, the existence of a resident genome with a different genetic code encoding the remaining 13 polypeptides) that are now established dogmas of modern biology. At the same time, the availability of highly efficient probes and imaging systems has allowed cell biologists to obtain a deep insight into how extracellular signals are conveyed and translated in living cells. An example of this insight has been the demonstration that a variety of extracellular stimuli cause a rise in intracellular Ca2+ concentration of high spatio-temporal complexity, that in turn is specifically decoded by intracellular effectors. Among these effectors are mitochondria themselves, that, endowed with low-affinity transport system for Ca2+, can however be recruited by microdomains generated in their proximity by the opening of Ca2+ channels.