Evaluation of autophagy in the AF cells under electronic microscope. Electron micrographs of annulus fibrosus (AF) cell after 24 hours of starvation. (a) AF cell in autophagy, observed by electronic microscopy in 8,000×. (b and c) A typical autophagosome in 50,000× and 150,000×. Double-limiting membrane could be observed in the autophagosome (arrowheads). The contents of the autophagosome might be a cellular organelle, mitochondria or RNA.