(K) WT MEFs carrying Su9-GFP were treated with DMSO or 10 ng/ml oligomycin for 1 h and viewed by laser scanning confocal microscopy for 30 min with 10-s intervals in the presence of TMRE. The arrows indicate mitochondria that showed flickering. Three frames from the time-lapse analysis are shown (please also see Movie EV1 and EV5). Scale bar, 10 µm. 