Effect of sympathetic de-activation on thermogenic function and membrane lipid composition in mitochondria of brown adipose tissue.

Male Long-Evans rats (9 weeks of age) were exposed to cold (5 degrees C) for 10 days. Then, sympathetic de-activation of brown adipose tissue (BAT) was performed either by BAT surgical denervation (Sy) or by warm re-exposure at 28 degrees C (WE) for 4 days. The incidence of the two treatments on thermogenic activity of BAT mitochondrial membranes and their lipid composition was investigated. Sy and WE induced a large decrease in GDP binding on the uncoupling protein (UCP) (43% and 82%, respectively). Several parameters of mitochondrial energization were investigated. Sy and WE substantially decreased UCP-dependent proton conductance (CmH+) over the whole range of protonmotive force. CmH+ showed greater variation than GDP binding. The low basal UCP-independent CmH+ was the same in all groups. Comparison of GDP binding and CmH+ with UCP content which is not modified revealed a masking of both the nucleotide binding site and the proton channel. Sy and WE induced the same increase of phosphatidylcholine to phosphatidylethanolamine ratio (16%) but had opposite effects on fatty acid unsaturation. The results were discussed with reference to functional significance of these variations in BAT mitochondrial thermogenic activity and lipid composition.