CHANGES OF MITOCHONDRIAL VOLUME AND FUNCTIONAL-ACTIVITY IN RELATION TO ION-TRANSPORT

We studied changes in mitochondrial volume, oxygen uptake, the state of mitochondrial pyridine nucleotides, and pH and potassium ion concentration in the external medium induced by an oxidation substrate or ADP (Phaseolus aureus Roxb.). It is established that rapid shrinkage of mitochondria occurred under the influence of succinate, such shrinkage being accompanied by alkalization of the medium and decline of potassium ion concentration. Oxygen uptake appeared later, at the same time as mitochondrial swelling, which was preceded by reduction of NAD(P). Addition of ADP led to increase in the rate of oxygen uptake, shrinkage of mitochondria, oxidation of NAD(P).H2, and ejection of protons from and entry of potassium into mitochondria. Proton ejection was soon replaced by alkalization of the medium. Reduction of NAD(P) occurred in clear correlation with changes in pH of the medium at the point of completion of shrinkage and was followed by swelling. The question of significance of the indicated processes to the task of ensuring mitochondrial functional activity is discussed in the paper. It is hypothesized that shrinkage of the organelles promotes establishment of contacts between components of electron transport chains (ETC) and coupling factors of the two opposed membranes needed for performance of phosphorylation.