Cold-induced changes in the energy coupling and the UCP3 level in rodent skeletal muscles

The mechanism of thermoregulatory uncoupling of respiration and phosphoryla tion in skeletal muscles has been studied. It is found that 24 h cold expos ure results in (i) a 3-fold increase in the amount of UCP3 protein in rat s keletal muscle mitochondria, and (ii) pronounced lowering of the membrane p otential in isolated rat or mouse skeletal muscle mitochondria. The decreas e in membrane potential is reversed by adding bovine serum albumin. Cold ex posure is also found to sensitize the membrane potential to the uncoupling action of added fatty acid (laurate). After laurate addition, the recouplin g effects of GDP and carboxyatractylate decrease whereas that of albumin in creases in mitochondria from cold-treated rats or mice. Changes similar to those induced by cold can be initiated by the in vivo addition of thyroxine . Cold exposure does not affect energy coupling in liver mitochondria. The possible involvement of UCP3 isoforms in nucleotide-sensitive and -insensit ive uncoupling is discussed. (C) 2001 Elsevier Science B,V. All rights rese rved.