Figure 7.

The diagram illustrates how radiation enhanced mitochondrial biogenesis and metabolic hyperactivation results in the increased formazan formation per cell. Ionizing radiation leads to increased intracellular Ca²⁺ (step 1), which further accumulates in mitochondria and activate mitochondrial biogenesis signaling (step 2). Activation of Ca²⁺ dependent signaling results in PGC-1α over-expression (step 3), which further transactivates the over-expression of Tfam (step 4), which induces mitochondrial biogenesis (step 5). Enhanced mitochondrial mass buffers cytoplasmic Ca²⁺ and turns in to metabolically hyperactive mitochondria (step 6).