Heat production and Na+-K+-ATPase enzyme units in lean and obese (ob/ob) mice

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Abstract
The ability of young obese (ob/ob) and lean mice to respond to a warm (33.degree. C) or a cold (14.degree. C) environment was evaluated. Heat production of obese and lean mice was more than 2 times greater at 14.degree. C than at 33.degree. C. Because stimulation of cellular thermogenesis by cold exposure was attributed in part to changes in Na pump activity, the number of Na+-K+-ATPase enzyme units in skeletal muscle, liver and kidneys of these mice was estimated from saturable [3H]ouabain binding to particulate tissue fractions. Neither phenotype nor environmental temperature influenced Kd values for specific ouabain binding. The concentration of ouabain binding sites in skeletal muscle and liver of cold-exposed obese and lean mice was approximately double the number observed in warm-exposed counterparts. Because cold-exposed obese mice had 43% less hindlimb muscle than warm-exposed obese mice the total number of [3H]ouabain binding sites in hindlimb muscle of cold-exposed obese mice was not elevated. Obese and lean mice housed at 14.degree. C had higher specific [3H]ouabain binding to kidney preparations than did preparations from mice housed at 33.degree. C but the temperature effect was somewhat less than observed in muscle and liver. Na+-K+-ATPase in young obese mice approximately responds to chronic cold exposure to approximately the same extent observed in young lean mice and changes in Na+-K+-ATPase parallel the increased heat production in the cold-exposed mice.