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Energy Costs of Ion Pumping by Animal Tissues²

Department of Animal Science, University of Alberta, Edmonton, Canada T6G 2P5

Results from recent in vitro studies indicate that in excess of 20% of the energy expenditure of skeletal muscle, duodenal epithelium and liver of domestic ruminants is to achieve Na⁺ and K⁺ transport across the plasma membrane. The energy cost of active Ca²⁺ transport is less clear but is likely less than 10% of the total expenditure of skeletal muscle at rest. Energy expenditure on Na⁺ and K⁺ transport was quite sensitive to the physiological state of the animal. During lactation, Na⁺ and K⁺ transport accounted for nearly half of the in vitro O₂ uptake of skeletal muscle, duodenal epithelium and liver. The energetic cost of supporting Na⁺ and K⁺ transport was also elevated in young, as compared with older animals, by feed intake and by exposure to cold. Na⁺ and K⁺ transport appears to be a substantial component of the maintenance energy expenditure of ruminant tissues. Its variation, therefore, implies that change of maintenance energy expenditures with physiological state of the animal warrants serious attention.

KEY WORDS: • maintenance energy expenditure • ion transport • energy cost of Na⁺,K⁺-ATPase • tissue respiration • Na⁺ and K⁺ transport • Ca²⁺-transport • changes in ion transport

² Work in our laboratory was supported by the Natural Sciences and Engineering Research Council of Canada and the Alberta Agricultural Research Council.

³ Current address: Department of Animal and Poultry Science, University of Guelph, Guelph, Canada N1G 2W2.

Manuscript received 6 March 1985. Revision accepted 28 June 1985.

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