Conformational basis of energy transduction in membrane systems. 8. Configurational changes of mitochondria in situ and in vitro.

Abstract

A method has been devised for the study of configurational changes in mitochondriain situ during the transition from nonenergized to energized conditions. The method depends upon the following component features: (a) subdivision of the tissue into finely diced sections; (b) the use of a modified Krebs-Ringer phosphate solution as the suspending medium; (c) aerobic conditions as the tactic for imposing the energized state; (d) anaerobic conditions or the presence of uncoupler under aerobic conditions as the tactic for imposing the nonenergized state; and (e) rapid fixation of the diced sections by addition of a mixture of formaldehyde and glutaraldehyde at a controlled temperature. Regardless of the tissue of source (heart, liver, skeletal muscle, retina, kidney) or the species (beef, rat, canary), all mitochondria show unambiguous configurational changes during the transition from nonenergized to energized conditions. The present study has revealed various optional features of the configurational states. Thus, there are two nonenergized configurations of the crista—orthodox and aggregated. The osmotic pressure of the suspending medium determines which nonenergized configuration will be observed. There are at least two variant forms of the energized-twisted configuration—tubular and zigzag. Again the osmotic pressure of the medium is an important factor in determining the form of the crista in the energized-twisted configuration. Mitochondria, such as those of heart muscle with relatively little matrix protein, show the clearest and most regular configurational changes, whereas mitochondria, such as those of liver with an abundance of matrix protein, show a more complex and less regular pattern of configurational change. From this comparative study of mitochondriain situ, it can be concluded that no exceptions have been found to the generalization that changes in configurational state of the cristae accompany changes in the energy state; this exact correlation provides additional support for the hypothesis of the conformational basis of energy transduction in the mitochondrion.