VARIATIONS IN ENERGIZATION PARAMETERS AND PROTON CONDUCTANCE INDUCED BY COLD ADAPTATION AND ESSENTIAL FATTY-ACID DEFICIENCY IN MITOCHONDRIA OF BROWN ADIPOSE-TISSUE IN THE RAT

Male weanling Long-Evans rats were fed on a low-fat semipurified diet (control diet, 2% sunflower oil; essential fatty acid (EFA) deficient diet, 2% hydrogenated coconut oil) for 9 weeks. In order to modulate need for non-shivering thermogenesis, groups of rats on each diet were exposed at 28°C (thermoneutrality) and at 5°C (cold acclimation) for the last 5 weeks. In brown adipose tissue (BAT) mitochondria, several parameters of mitochondrial energization, protonmotive force (Δp) and its components ΔpH and membrane potential, Δψ, were investigated. Simultaneous measurement of oxygen consumption and Δψ (the main component of Δp) was performed by varying α-glycerophosphate concentration and the force / flux relationship of the mitochondria was established by comparison of proton conductance, CmH, over the whole range of protonmotive force, Δp. In the absence of GDP, at 28°C, EFA deficiency induced a marked increase in CmH. Cold acclimation led to comparable enhanced CmH in control and EFA-deficient mitochondria. In the presence of GDP which binds and inhibits the BAT 32 kDa uncoupling protein, CmH was the same in 28°C and 5°C control mitochondria, but EFA deficiency led to an enhanced GDP independent CmH at 28°C and to a lesser extent at 5°C. These results are discussed with reference to substantial changes in mitochondrial lipid composition induced by the deficiency. © 1990.