Electron microscopic tomography of rat-liver mitochondria and their interaction with the endoplasmic reticulum.

Electron microscopic tomography can provide a complete three-dimensional range of information about subcellular structures. Applied to mitochondria, it has shown that the conventional textbook model of this organelle is incorrect. The infoldings of the inner membrane (called cristae) are connected by narrow tubular regions to each other and to the outside, suggesting that internal diffusion of ions, metabolites and proteins may be restricted. Tomographic reconstruction of mitochondria in situ indicates these organelles may occur in clusters with stacks of endoplasmic reticulum, forming extended structures that may be involved in [Ca++] regulation.