Fig. (6).

Possible relationships between nutrient availability, cell stress, cytosolic Ca²⁺ levels and autophagy. Starvation and an increased cell stress correlate with a high level of cytosolic Ca²⁺ generated from the ER and/or mitochondria and this induces autophagy. On the other hand, when nutrients are available to cells and no stress occurs, cytosolic Ca²⁺ remains at a low level and, consequently, basal autophagic activity is maintained.