Observations of globular membranes and apparent elementary particles in rat mitochondria, in situ.

Ultrastructural details of rat skeletal muscle, fixed in a PIPES-buffered glutaraldehyde solution, included the globular configuration of the outer and inner mitochondrial membranes as well as small transparent particles (80--100A diameter) distributed throughout the matrix of these organelles. The size of these particles and their intimate relationship with the innermost surface of the cristae suggests that they may represent an in situ visualization of the elementary particles once reported in intact cells and frequently observed in negatively stained mitochondrial preparations. The membrane configurations and particles were not discernable in these tissues when a phosphate buffer system was used in the fixation regimen.