Reversal of various types of mitochondrial swelling by adenosine triphosphate.

A number of agents have been shown to cause swelling of mitochondria in vitro. These include five substances of known intracellular occurrence, namely, thyroxine (l-3)) inorganic phosphate (4, 5), Ca++ (I, 4), reduced glutathione (6), and the unidentified endogenous uncoupling agent, U factor (7). In addition, other agents such as p-chloromcrcuribenzoate (8)) arsenate (5), Zn++ (5), phlorizin (9), and simple hypotonicity (4) also cause mitochondrial swelling. In preceding papers it has been demonstrated that the mito,chondrial swelling produced by thyroxine may be readily reversed with extrusion of water by addition of ATP alone (3, 10). Qther nucleoside triphosphates were inactive. The reversal by ATP occurred in a buffered saline medium or in distilled water, but not in 0.3 M sucrose media. It may proceed independently of respiration and phosphorylation, since it is not inhibited by dinitrophenol or cyanide. However, it is inhibited by azide, arsenate, Dicumarol, and gramicidin, suggesting some relationship of mitochondrial contraction to intermediate reactions of oxidative phosphorylation. It became of interest to determine whether mitochondrial swelling produced by agents other than thyroxine could also be reversed by a similar ATP-dependent process in view of some indications that the swelling induced by different agents may differ in chemical mechanism and in the morphological configuration produced (6, 9). Also, earlier experiments showed that spontaneous mitochondrial swelling could not be reversed by ATP under conditions which were adequate for reversal of thyroxine-induced swelling (10). This paper describes the results of a comparative survey of the requirements for ATP-linked reversal of mitochondrial swelling induced by a wide variety of agents. The results show that only thyroxine-induced swelling can be reversed by addition of ATP alone but that mitochondrial swelling produced by Ca++, phosphate, U factor, oleate, hypotonicity, phlorizin, and other agents can also be reversed in vitro by ATP if Mg++ (or Mn++) and serum albumin or EDTA’ are also present, in addition to ATP. The findings point to an ATP-specific mechanism, possibly contractile in nature, which can cause reversal of mitochondrial swelling induced by a variety of agents.