The role of Ca2+ changes in the commitment to apoptosis has been appreciated for more than two decades. However, early work focused on increases in cytosolic Ca2+ levels that may not be associated with most examples of programmed cell death. Rather, recent studies indicate that release of Ca2+ from the endoplasmic reticulum (ER) and subsequent mitochondrial Ca2+ uptake plays a more important role by regulating release of cytochromecfrom mitochondria. These apoptosis-associated Ca2+ fluxes are regulated by members of the BCL-2 family of proteins and may therefore be critical targets of their evolutionarily conserved actions. Therefore, the availability of reliable techniques for measuring organelle-associated Ca2+ fluxes is critical to ongoing research in the field, yet these techniques present unique challenges not associated with the more routine measurements of cytosolic Ca2+ levels. In this chapter, we provide detailed methods for measuring cytosolic, ER, and mitochondrial Ca2+ levels in whole using commercially available fluorescent dyes, identifying key potential pitfalls and alternative strategies.
