Ion transport by heart mitochondria. XXII. Spontaneous, energy-linked accumulation of acetate and phosphate salts of monovalent cations.

Abstract The accumulation of monovalent cations by isolated beef heart mitochondria has been studied by evaluating the efficiency of energy-dependent osmotic swelling. Extensive osmotic swelling occurs spontaneously when isolated heart mitochondria are suspended in 0.1 m acetate or phosphate salts. The swelling and ion uptake depend on either respiration or the presence of exogenous ATP, and the initial rate of swelling is proportional to the initial rate of respiration or ATP hydrolysis, respectively. The efficiency of the reaction varies somewhat from preparation to preparation but approaches a limit of about 2 cations accumulated per pair of electrons traversing a phosphorylation site. All monovalent cations tested support the reaction, but the most efficient energy-dependent swelling occurs with K + . Weak acid anions are required for the ion accumulation and swelling and the reaction appears to depend on the amount of free acid available in the suspension. Permeant strong acid anions, such as NO 3 − , fail to support the swelling reaction in the presence of energy. Valinomycin increases both the amount and the efficiency of ion uptake under these conditions. Mg 2+ decreases both of these values whereas p -chloromercuriphenyl sulfonate increases both. These responses are discussed in terms of current models of mitochondrial ion transport.