Brown‐Adipose‐Tissue Mitochondria

Abstract

1.Endogenously uncoupled mitochondria from the brown adipose tissue of cold-adapted hamsters, rats and guinea-pigs swell in KC1, KBr, KNO, 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.2. Albumin has no effect on the swelling rates in these potassium salts plus valinomycin, but is strongly inhibitory with both potassium salts plus nigericin and wit,h 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. 3.These results are interpreted in terms of electrogenic entry of C1-, Br-, NO,-and CNS-, and of a high native proton permeability which is abolished by albumin.4. GDP inhibits swelling in KC1 and KBr in the presence of either valinomycin or nigericin. The inhibition is not reversed by uncoupler. Exchange of 38Cl-both into and out of the sucroseimpermeable space is strongly inhibited by GDP. The effectiveness of different nucleotides in inhibiting 36Cl-efflux is identical t o their effectiveness previously observed for uncoupler-releasable respiratory inhibition in the presence of albumin.5. GDP 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 permation is observed which may be reversed by carbonyl cyanide p-trifluoromethoxyphenylhydrazone.6. The entry of sodium appears to be by electroneutral exchange and not to be affected by albumin or nucleotide.7. The use of the ion permeability properties as a tool to investigate the relationship between membrane structure and energy conservation is discussed.Mitochondria prepared from brown adipose tissue of cold-adapted hamsters, rats or guinea-pigs show no evidence of energy conservation when prepared by methods which are appropriate for other tissues [I to 41. I n order to demonstrate uncoupler stimulation of respiration it is necessary both to remove fraction of the endogenously bound fatty acids, either by oxidation [4] or by addition of albumin [5], and also to provide a nucleotide in the incubation medium [6,6]. Very little information is currently available as to the mode of action of the added nucleotides, except that their action is to raise the energy potential of the respiring mitochondrion, as judged by phosphate potential mitochondria1 energy conservation and ion permeation, the previous observation from this laboratory [9] of a substantial permeability to chloride of hamster brown-adipose-tissue mitochondria (at neutral p H in the absence of respiration) has prompted this study to determine whether factors which influence energy conservation are effective in modifying the ion permeability properties of brownadipose-tissue mitochondria. MATERIALS AND METHODSRat-liver and heart mitochondria were prepared from animal...

Fatty acid circuit as a physiological mechanism of uncoupling of oxidative phosphorylation

“…It is interesting that non-specificity of the thermogenin-induced conductance was already recognized by its first students, Nicholls and Lindberg [28], who found that brown fat mitochondria are permeable not only to H ~ but ~lso to CI-. Garlid and co-workers [27, 29,31] reconstituted CI-transport in thermogenin proteoliposomes and ~hnwccl that, ~_!nlike in the case of H* transport, fatty anions are no: nece~:~ary for this process.…”

Carnitine cycle in brown adipose tissue mitochondria as a tool for studying the regulatory role of fatty acids in the uncoupling protein function

“…Apart from other types of mitochondria they possess the uncoupling protein (UP), a unique proton translocator [2,3], converting A/~H + into heat. H + fluxes through the UP are inhibited by purine nucleotides [4][5][6][7][8] and activated by fatty acids [3,[8][9][10]. Both regulatory mechanisms were also demonstrated in a reconstituted system [3], but the activation by fatty acids was disputed in another laboratory [2].…”

Regulation of GDP binding and uncoupling-protein concentration in brown-adipose-tissue mitochondria. The effects of cold-acclimation, warm-reacclimation and noradrenaline

“…In order to relate changes in GDP binding to the function of the proton conductance pathway, mitochondrial swelling and GDP binding were assayed on BAT mitochondria prepared from rats housed at 22 "C or at 4 "C for either 3 h or 7 days. Mitochondrial swelling, in the presence of potassium acetate and valinomycin, is an indication of the proton permeability of the mitochondrial inner membrane (Nicholls & Lindberg, 1973;Rial & Nicholls, 1984). Fig.…”

“…Mitochondrial permeability to protons was determined as the initial rate of swelling of non-respiring mitochondria in iso-osmotic media containing valinomycin (Nicholls & Lindberg, 1973). Mitochondria were prepared by the procedure outlined above but in 250 mmsucrose/5 mM-Tes/1 mM-EDTA, pH 7.2 at 4 'C.…”