Role of anions in mitochondrial swelling and contraction

Abstract

Summary 1. The effects of large anions on mitochondria, as compared with chloride, are: (a) Increase in rates of swelling, (b) Increase in rates of oxygen uptake, (c) Inhibition of metabolic contraction, (d) Acceleration of the loss of inorganic phosphate from mitochondria. 2. Addition of agents, which cause contraction and restoration of intramito-chondrial concentration of ATP (EDTA or ATP) in chloride buffers, causes further swelling and loss of intramitochondrial ATP (EDTA only) in buffers, containing large anions. 3. Large anions do not alter the semipermeable properties of mitochondrial membranes, i.e ., osmotic contraction of sodium acetate loaded mitochondria by addition of sucrose can be obtained. 4. Swelling by large anions is independent of respiration. 5. Addition of sulfhydryl reagents which add negative charge to mitochondria ( p -chloromercuriphenylsulfonate) markedly increases swelling under all conditions. However, inactivation of mitochondrial sulfhydryl groups by sulfhydryl reagents which do not add negative charge also does not cause swelling. Both reagents completely inhibit respiration in mitochondria. 6. The above data are interpreted to indicate that mitochondrial shrinking and swelling is very similar to gel—sol transformations of myosin gels, which phenomena is accomplished by alterations in surface charge of the gels. These surface charges are specifically altered by the binding of such substances as Ca 2+ , Mg 2+ , ATP, and p -chloromercuriphenylsulfonate to the gels.