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Previous data suggested that reversible structural changes occur in mammalian kidneys exposed to hypoxia. Since one of the concomitants of tissue hypoxia is 'swelling,' with an uptake of external sodium ion, the formed elements of kidney homogenates were isolated in media containing 0.15 M NaCl, 0.15 M KCl, or 0.3 M sucrose in order to mimic ionic conditions surrounding these structures in normoxic and hypoxic conditions and to compare these with usual nonionic isolation procedures capable of producing relatively intact structures. NADH oxidase, ATPase, and light-scattering changes on acidification were measured. It was found that both cations had deleterious effects on NADH oxidase and light-scattering changes of mitochondrial and microsomal fractions. The 0.15 M KC1 acted as a stimulator of microsomal ATPases and supported mitochondrial ATPases. The 0.15 M NaCl caused a dramatic inhibition of mitochondrial ATPases, but produced nearly the same microsomal ATPase activity as microsomes isolated in sucrose. These results indicate rather dramatic regulatory effects of monovalent cations on energy-utilizing (ATPases) and energy-producing (NADH oxidases) cellular reactions, together with striking effects on sensitivity of structural elements to changes in hydrogen ion content, as shown by light-scattering measurements. (Author)