Ionic environment and the contraction of isolated rat-liver mitochondria by adenosine triphosphate

Abstract

Contraction of thyroxine-swollen rat-liver mitochondria by adenosine triphosphate is essentially independent of the ionic environment, since it proceeds maximally in media containing K +, Na +, Li +, Rb +, NH 4 4 or Tris ++ as major cation or Cl −, Br −, I −, F −, NO 3 −, ClO 3 −, ClO 4 −, SO 4 =, or acetate − as major anion. Contraction also occurs over a wide range of osmolarity, as well as in distilled water with minimum possible ionic strength. The adenosine triphosphate-induced contraction also occurs in mitochondria in which the ability for oxidative phosphorylation and for specific K +-binding is completely lost by aging. These findings thus exclude the possibility that water extrusion from mitochondria by adenosine triphosphate is indirect and dependent on active ion fluxes between extra- and intramitochondrial compartments. It is therefore more probable that adenosine triphosphate produces a contractile change in the membrane leading to a decrease in volume by extrusion of water and at least some low-molecular weight solutes.