Effect of mitochondrial clustering on O2 supply in hepatocytes.

Isolated rat hepatocytes were treated with digitonin to selectively disrupt the plasma membrane and allow study of the O2 dependence of mitochondria within the cell cytoskeleton, but without cytosol. Half-maximal oxidation of cytochrome c occurred at 2.0 microM O2 in treated cells incubated under State 3 conditions, whereas in intact cells it was 6.0 microM and in isolated mitochondria (State 3) 0.69 microM. the intermediate value for treated cells indicates that both the geometry of mitochondrial packing and the intracellular diffusion coefficient are important in determining intracellular mitochondrial O2 dependence. Analysis of intracellular diffusion, assuming that the mitochondrial clustering increases the effective mitochondrial radius, indicates that an intracellular diffusion coefficient of between 10(-6) and 4 X 10(-6) cm2 . s-1 and an effective mitochondrial radius of approximately 2 micron would account for the observed intracellular O2 dependence of mitochondrial function.