Abstract

In recent years, mitochondria have emerged as important targets of agonist-dependent increases in cytosolic Ca 2+ concentration. Here, we analyzed the significance of Ca 2+ signals for the modulation of organelle function by directly measuring mitochondrial and cytosolic ATP levels ([ATP] m and [ATP] c , respectively) with specifically targeted chimeras of the ATP-dependent photoprotein luciferase. In both HeLa cells and primary cultures of skeletal myotubes, stimulation with agonists evoking cytosolic and mitochondrial Ca 2+ signals caused increases in [ATP] m and [ATP] c that depended on two parameters: ( i ) the amplitude of the Ca 2+ rise in the mitochondrial matrix, and ( ii ) the availability of mitochondrial substrates. Moreover, the Ca 2+ elevation induced a long-lasting priming that persisted long after agonist washout and caused a major increase in [ATP] m upon addition of oxidative substrates. These results demonstrate a direct role of mitochondrial Ca 2+ in driving ATP production and unravel a form of cellular memory that allows a prolonged metabolic activation in stimulated cells.