**1.5 Confocal microscopy**

LSMLGPI cells were seeded onto glass coverslips and exposed to IR. The mitochondria were stained with a probe as described by Claro [20] in living cells.

For analysis of the KΨmito, 0.5 μM DiOC6(3) was used in DMEM, in vivo. The fluorescence was measured between 546/500 nm. To confirm the mitochondrial accumulation of DiOC6(3), the cells were incubated with KΨmito inhibitors [34] for different periods of time.

## **1.6 Electron micrography**

The cells were seeded as described by Claro [21], and were then radiated and fixed before being analyzed with a transmission electron microscope (1200 EXII, JEOL, Tokyo, Japan).
