Ultrastructural analysis of isolated Rh-123^low (A) and Rh-123^high (B) HSC. The original magnification was 8,200X in each case. Pronounced mitochondrial clustering is apparent in the nuclear cleft region of the Rh-123^high cell (B), correlating with the bipolar perinuclear localization of Rh-123 staining seen in Fig 7B. Activated mitochondria in (B) can be identified by increased electron density due to thickening of cristae and by the characteristic structural collapse and “wagon wheel” appearance of actively respiring mitochondria; these features were rarely noted in micrographs of Rh-123^low cells (A). The micrographs are representative of 17 images of Rh-123^low cells and 32 images of Rh-123^high cells.