Studies on the mechanism by which anaerobiosis prevents swelling of mitochondria in vitro: effect of electron transport chain inhibitors.

Several years ago it was observed that strict anaerobiosis prevented the swelling of isolated liver mitochondria. This was true for spontaneous swelling and for swelling induced by phosphate, certain metal ions, and other substances (l-3). This observation created a sharp paradox with the generally accepted view that adenosine triphosphate or active phosphorylation was essential in maintaining mitochondrial structure and integrity (4, 5), for under anaerobic conditions one would expect the mitochondrial ATP level to fall to low levels. Subsequent studies1 (6-S) have indicated that anaerobiosis protects against virtually every agent known to induce mitochondrial swelling by a selective action. In addition, the unexpected observation that some uncoupling agents, like 2,4-dinitrophenol, can prevent mitochondrial swelling has been firmly established as fact (7, 9-11). In our earlier experiments (1) we concluded that blocking the electron transport chain at cytochrome oxidase with NaCN did not result in protection against swelling, whereas anaerobiosis did. This resulted in the suggestion that the effect of anaerobiosis was to prevent some easily oxidizable group in the mitochondrial membrane from undergoing the oxidative change essential for the permeability change responsible for swelling. In reinvestigating this question, Lehninger and Ray (6) observed good protection with 1O-3 M NaCN. They postulated (6, 7) that the action of anaerobiosis and NaCN resulted in keeping one or more components of the electron transport chain in the reduced form. This paper reports additional studies which bear on the possible role of the state or the activity of the electron transport chain in controlling the permeability of the mitochondrial membrane and thereby determining mitochondrial swelling. Using dilute mitochondrial suspensions we have obtained effects with NaCN very similar to those reported by Lehninger and Ray (6, 7). The exact reason for the discrepancy with the earlier results with more concentrated suspensions has not been established. Studies with other blocking agents for the electron transport chain and with various substrates suggest that active electron transfer or some dynamic state is essential for swelling rather than just the oxidized state. Blocking the electron trans-