Brown-Adipose-Tissue Mitochondria

The Influence of Albumin and Nucleotides on Passive Ion Permeabilities



  • 1Endogenously uncoupled mitochondria from the brown adipose tissue of cold-adapted hamsters, rats and guinea-pigs swell in KC1, KBr, KNO3 and KCNS in the presence of valinomycin. Identical rates of swelling are obtained employing the ammonium salts or the potassium salts in the presence of nigericin.
  • 2Albumin has no effect on the swelling rates in these potassium salts plus valinomycin, but is strongly inhibitory with both potassium salts plus nigericin and with ammonium salts. Albumin inhibits swelling in potassium phosphate plus valinomycin but is without effect in potassium phosphate plus nigericin or in ammonium phosphate. All these inhibitions may be reversed by uncoupler.
  • 3These results are interpreted in terms of electrogenic entry of Cl-, Br-, NO3- and CNS-, and of a high native proton permeability which is abolished by albumin.
  • 4GDP inhibits swelling in KCl and KBr in the presence of either valinomycin or nigericin. The inhibition is not reversed by uncoupler. Exchange of 36Cl- both into and out of the sucroseimpermeable space is strongly inhibited by GDP. The effectiveness of different nucleotides in inhibiting 36Cl- efflux is identical to their effectiveness previously observed for uncoupler-releasable respiratory inhibition in the presence of albumin.
  • 5GDP only partially inhibits NO3- permeation and is without demonstrable effect on thiocyanate, phosphate or acetate entry, but only if no proton movements are involved. Otherwise, in these systems, some limitation of proton permeation is observed which may be reversed by carbonyl cyanide p-trifluoromethoxyphenylhydrazone.
  • 6The entry of sodium appears to be by electroneutral exchange and not to be affected by albumin or nucleotide.
  • 7The use of the ion permeability properties as a tool to investigate the relationship between membrane structure and energy conservation is discussed.