Morphological changes in isolated rat-liver mitochondria during swelling and contraction

Morphological changes of rat-liver mitochondria brought about by swelling and ATP-induced contraction were studied by electron microscopy. The course of swelling is proposed to be as follows: Entering of water (and solutes) causes breakage of the outer membrane and formation of protrusion of the inner membrane. The distention of the inner membrane is accompanied by loss of density of the matrix and by disapperance and change of shape of the cristae, probably due to their unfolding and evagination. Both membranes seem to possess a limited ability to stretch.

Addition of ATP to mitochondria swollen in the presence of either orthophosphate, oleate and thyroxine gave rise to structures different from mitochondria before the onset of swelling. Restoration of the mitochondrial morphology was not observed. It is thought that the processes initiated by ATP are not a simple reversal of swelling.