MECHANISM OF MITOCHONDRIAL SWELLING .3. 2 FORMS OF ENERGIZED SWELLING

The characteristics of energized swelling of beef heart mitochondria are described and compared with those of pseudoenergized swelling. Both processes are ultimately dependent upon ion gradients. The essential difference between these two types of swelling resides in the way the ion gradient is generated. In pseudoenergized swelling in sucrose-free media containing certain alkali metal salts (e.g., sodium acetate), the salts readily penetrate the mitochondrion by passive or facilitated diffusion and achieve an equilibrium distribution determined by the Dorman effect. As a result of this equilibration and Donnan distribution, swelling takes place. In energized swelling in a sucrose-free medium containing appropriate alkali metal salts (e.g., potassium acetate), swelling is also the result of the equilibration of salts coupled with the resulting Donnan ion distribution. However, in the latter case the penetration of the cristael membrane by salts is achieved by energy dependent translocation rather than by passive or facilitated diffusion. In energized swelling in sucrose media, the salt must be concentrated interiorily by an active transport mechanism. Translocation of ions thus leads to accumulation of sufficient salt in the osmotically active space to provide an osmotic gradient in excess of that imposed by the sucrose medium, and swelling takes place. Energized swelling in sucrose-free media can be arrested by addition of uncouplers or of reagents which inhibit the energizing process. Energized swelling in sucrose-containing media is not only arrested, but also the process is reversed by the addition of these reagents. Pseudoenergized swelling is neither arrested nor reversed by this means. However, imposition of an external osmotic gradient by addition of sucrose can reverse pseudoenergized swelling and can reverse energized swelling in a sucrose-free medium which has been arrested by addition of respiratory inhibitors. © 1969.