Freeze-fracture studies on mitochondrial membranes of spermatocytes.

Separation of the two-folded lamina of the mitochondrial cristae occurs in mitochondria of spermatocytes and spermatids. Freeze-fracture exposes large areas of the inner and outer halves of the inner membrane. The surface of the outer half of the inner membrane is concave, with small numbers of intramembranous particles (IMPs). Its distinctive feature is the presence of protruding particles surrounding a pit. On the inner half of the inner membrane, there are large numbers of densely-packed, irregularly-distributed IMPs, among which regular pits are seen. Morphometric analysis and reconstructions suggest that these structures are "channels" in the mitochondrial membrane with an internal diameter of approximately 18 nm. It is uncertain whether such mitochondrial structures are confined to the spermatocyte or whether they may also occur in other cells.