Intracellular ATP Levels: Challenge to the Current Consensus and Its Implications for Intracellular Signaling

Work with novel indicators that report intracellular ATP concentrations with improved spatial and temporal resolution have challenged the current consensus that under physiological conditions, intracellular ATP concentrations are not rate-limiting to enzymatic reactions. Recent data from cardiac myocytes and cultured neurons show marked fluctuations of intracellular ATP levels, as well as evidence for compartmentalization. It is likely that the availability of these genetically encoded indicators will produce rapid progress in the mapping of the dynamics of intracellular ATP concentrations in various types of cells. Here, a brief account of the most recent indicators is provided as well as a review of how natural evolution appears to have obviated the potential shortage of the ATP supply to one of key enzymes of the cyclic AMP signaling cascade, adenylyl cyclase 9.