Figure 6. Substructure measurements of rod and cone mitochondria from 3-D tomographic reconstructions

Measurements were conducted, using the NIH Image program, on the tomographic reconstructions from seven rods and seven cones from four different mice on equally spaced slices through their volumes. The histograms represent means ± SEMs. A two-tailed Student's t-test was used to determine significant differences: *p < 0.05; **p < 0.005. A, B, and C: Comparison of cristae measurements. The reconstructed portion of the mitochondrion was segmented along membranes: outer membrane, inner boundary membrane and cristae membranes. The program XDend calculated the volume and surface area values for the outer membrane (used for "mito" in the denominator) and each crista. The values for individual cristae were summed to provide the numerator of the ratios (a and b) or number per volume C. Examples of "segments" and "constrictions" are shown in Figure 2. D: Surface density of contact site classes. Contact sites were divided into two classes: classical and bridge. The classical contact site is where the outer and inner boundary membranes join together, whereas the bridge contact site spans across the intermembrane space (forms a bridge) without a change in distance between the outer and inner membranes [52]. E: Size of mitochondrial substructures. The outer to inner membrane distance was measured perpendicular to the membranes, from the outer edge of the outer membrane through to the inner edge of the inner membrane at randomly selected points along the periphery that were not contact sites. The contact width was measured perpendicular to the membranes, from the outer edge of the outer membrane through to the inner edge of the inner membrane. The contact diameter was measured parallel to the membranes. The crista junction is the largest opening at sites where the inner boundary membrane involutes into the interior. The crista width is the width of the intracristal space at randomly selected points along cristae at sites other than junctions. All sizes are in nanometers (nm).