Vibeke S. M. Bernson

The Identification of the Component in the Inner Membrane of Brown Adipose Tissue Mitochondria Responsible for Regulating Energy Dissipation

The proton conductance of the inner membrane of hamster brown adipose tissue mitochondria can be regulated in vitro by exogenous purine nucleotides, which bind to a component on the outer face of the inner membrane. This unique mechanism has been proposed to represent the molecular site of non-shivering thermogenesis in this tissue. Using a photo-affinity analogue of ATP, we have identified the nucleotide binding component as a protein of 32,000 daltons.

Metabolic consequences of limited substrate anion permeability in brown fat mitochondria from a hibernator, the golden hamster

Brown fat mitochondria obtained from a hibernator, the golden hamster, were investigated in order to elucidate the significance of membrane permeability for metabolic functioning at different temperatures. The mitochondria were shown to have active permeases for phosphate and pyruvate, but very poorly developed permeases for di- and tricarboxylate substrate anions. This was shown with both osmotic swelling techniques and respiration-driven uptake studies. It was shown that the very limited malate permeation observed was compatible with it being a non-carrier-mediated diffusion process. The role of malate transport in supporting fatty-acid oxidation in vitro as a function of temperature was studied in detail. The results support our earlier suggestion that physiologically pyruvate carboxylase probably functions to generate oxaloacetate when high concentrations of condensing partner are needed during thermogenesis. They may also explain earlier observations that acetate was produced from palmitoyl-carnitine at low temperatures even when malate was present; this is here shown to be due to the limited malate permeability at these low temperatures. Thus, even at the body temperature of the hibernating hamster (4-5 degrees C), brown fat is probably able to combust fatty acids totally.

A comparison of the cellular toxicity of exhausts from cars driven on present and future fuels

A cellular test system (brown-fat-cell-test) (BFC-test) has been used to evaluate the toxicity of the particulate phase of exhaust emission from vehicles fuelled with gasoline and alcohol-mixed fuels. The results were evaluated by an analysis of variance with multiple contrasts. The exhaust extracts from cars driven on commercially available gasoline were found to be significantly more toxic to the cellular oxygen consumption than a similar extract of exhausts from cars driven on alcohol-mixed fuels. The lowest toxicity was found with extracts from catalyst processed exhausts.

The evaluation of air sample extracts on the phagocytosis of alveolar macrophages and studies of macrophage-mediated mutagenesis in co-cultivated V79 Chinese hamster cells

Abstract The purpose of utilizing rabbit pulmonary alveolar macrophages (PAMs) in screening air sample extracts for cytotoxicity, was to evaluate particulate air pollutants from a biological point of view, using a relevant cell type. Phagocytic capacity of PAMs was used as the test parameter. The cytotoxicity of extracts of particulate air pollutants (φ 50 ) was determined and expressed as μg particles per mL medium. The mean values of samples representing five tested categories of environmental conditions was evaluated: a rural area, IC = 471 μ g/mL; a city street, IC 50 = 270 μ g/mL; a roof of a five-storied city building, IC 50 = 124 μ g/mL; a tunnel for automotive traffic, IC 50 = 143 μ g/mL; gasoline exhaust particles, IC 50 = 5 μ g/mL. Since air sample extracts have been shown to be mutagenic, the influence of particle ingestion (phagocytosis) on macrophage-mediated mutagenesis of polycyclic aromatic hydrocarbons in V79 Chinese hamster cells was studied. The results suggest that the mutagenicity of 7,8-dihydroxy-7,8-dihydro-benzo(α)pyrene is enhanced tenfold when PAMs are stimulated with particles. The mechanism by which the phagocytic uptake of particles by the PAMs enhanced the mutagenicity of the PAH can so far only be a matter for speculation.

SUCCINATE OXIDATION IN HAMSTER BROWN ADIPOCYTES.

In a suspension of isolated hamster brown adipocytes succinate can be oxidized at a high rate. This oxidation capacity is found to be mainly extracellular and can be totally blocked by the SH-reagent DTNB. In the intact cell succinate is found to be oxidized very slow probably as a function of a low transport rate over the membrane(s). Succinate potentiates, however, NE-induced respiration by supplying a condensing partner for entry into the citric acid cycle, thereby promoting a higher rate and extent of acetyl CoA oxidation.