The Acute Regulation of Mitochondrial Proton Conductance in Cells and Mitochondria from the Brown Fat of Cold‐Adapted and Warm‐Adapted Guinea Pigs

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Abstract
Cells and mitochondria were prepared from the brown adipose tissue of adult guinea-pigs adapted to either 4.degree.-7.degree. C or 22.degree.-25.degree. C. The cold-adapted cells displayed noradrenaline[norepinephrine]-stimulated, propranolol-sensitive respiration but noradrenaline failed to increase the respiration of the warm-adapted cells. Purine-nucleotide-sensitive proton conductance was greater in cold-adapted mitochondria than in warm-adapted controls. At the same time cold-adapted mitochondria were extremely sensitive to the uncoupling effect of endogenous and infused fatty acids, and resembled the mitochondria from the brown adipose tissue of cold-adapted hamsters. Warm-adapted mitochondria were 9-fold less sensitive, and resembled liver mitochondria. With cold-adapted, but not warm-adapted mitochondria, respiration increased proportionately to the rate of fatty acid infusion. The presence of the 32,000-MW proton conductance pathway is necessary for the expression of a high sensitivity to fatty acid uncoupling, suggesting that the fatty acids interact directly with this protein to modulate the proton conductance during the acute regulation of thermogenesis.

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