(41) A THERMODYNAMIC MODEL TO PREDICT THE FOLDING OF THE INNER MEMBRANE OF MITOCHONDRIA

C. Renken¹, G. Perkins², G. Siragusa¹, P. Salamon¹, M. Ellisman² and T. Frey^1
1San Diego State University, Department of Biology, San Diego, CA 92182
²NCMIR University of California, San Diego, CA

The use of electron tomography in the study of mitochondria has lead to a better understanding of the topology of the inner membrane. One feature of crista junctions in orthodox mitochondria is their uniform diameter of approximately 30 nm observed in mitochondria studied in situ from rat brain, brown fat, sciatic nerve, chick cerebellum, and N. crassa. Similar structures were found by Mannella et al. (1994) in rat liver mitochondria both in situ and in purified mitochondria. An exception is seen in isolated mitochondria of various sources; these mitochondria have a very condensed matrix space and enlarged crista junctions. Under some circumstances, when the matrix volume of these mitochondria increases, crista junctions become smaller (mean of 24 nm) and may even pinch off, leaving some cristae unattached to the inner boundary membrane. These observations suggest that while there may be some regulation of crista junction diameter in orthodox or moderately condensed mitochondria, large changes in osmotic pressure across the inner mitochondrial membrane that cause extreme changes in matrix volume, disrupt whatever forces stabilize crista junction size.

We are attempting to model these changes based on the energy of membrane curvature. Starting with the simplest assumption that the inner membrane is a simple vesicle and its curvature energy is minimized for a given surface area and enclosed volume, we explain the nature of crista junctions as thermodynamically stable structures that minimize the bending energy involved in forming such junctions. A theoretical model is built from shape equations constrained by the total membrane energy of the inner membrane, and predictions from this model are compared with experimental results from mitochondria fixed at varying osmotic conditions.

© 1999 Wadsworth Center, All Rights Reserved. Legal & Privacy Notices