Ion transport underlying metabolically controlled volume changes of isolated mitochondria.

An earlier study has indicated that the swelling of isolated mitochondria induced by inorganic phosphate (P(i)) can be accounted for largely or completely by the accumulation of ions. In the present study, a similar uptake was shown to be induced by a wider range of P(i) concentrations. Addition of ADP, KCN, or 2,4-dinitrophenol initiates a shrinkage which can be accounted for by the efflux of ions. The results are consistent with the explanations that (a) P(i) induces a transport of ions and a concomitant osmotic swelling, and (b) the addition of substances which compete or interfere with the energy available for transport results in ion efflux and a corresponding mitochondrial shrinkage. The results are not consistent with proposals that the changes in the light scattered by mitochondrial suspensions with alterations in metabolic states reflect a mechanochemical coupling phenomenon.