Abstract
1. The excessive accumulation of Ca(2+) by mitochondria suspended in an iso-osmotic buffered potassium chloride medium containing oxidizable substrate and phosphate led to extensive swelling and release of accumulated Ca(2+) from the mitochondria. When the Ca(2+) was removed from the medium by chelation with ethylene glycol bis(aminoethyl)tetra-acetate, the swelling was reversed in a respiration-dependent contraction. The contracted mitochondria were shown to have regained some degree of respiratory control. 2. The respiration-dependent contraction could be supported by electron transport through a restricted portion of the respiratory chain, and by substrates donating electrons at different levels in the respiratory chain. 3. Respiratory inhibitors appropriate to the substrate present completely inhibited the contraction. Uncoupling agents, and the inhibitors oligomycin and atractyloside, were without effect. 4. When the reversal of swelling had been prevented by respiratory inhibitors, the addition of ATP induced a contraction of the mitochondria. In the absence of added chelating agent the contraction was very slow. The ATP-induced contraction was completely inhibited by oligomycin and atractyloside, was incomplete in the presence of uncoupling agents and was unaffected by respiratory inhibitors. 5. The relationship between the energy requirements of respiration-dependent contraction and the requirements of ion transport and other contractile systems are discussed.