EFFECTS OF COLD ENVIRONMENT ON MITOCHONDRIAL GENOME EXPRESSION IN THERAT - EVIDENCE FOR A TISSUE-SPECIFIC INCREASE IN THE LIVER, INDEPENDENT OF CHANGES IN MITOCHONDRIAL GENE ABUNDANCE

The abundance of the mitochondrially encoded mRNA for subunit II of cy tochrome c oxidase (COII mRNA) increases in the liver of rats exposed to environmental cold stress (4-degrees-C ambient temperature). Only t ransient increases or no changes in COII mRNA levels were observed in brown fat and soleus muscle respectively. The time course of the liver COII mRNA increase was compared with the effects of cold stress on mi tochondrial 16S ribosomal RNA expression and indicated that cold induc es a rapid (few hours) increase in the liver mitochondrial mRNA levels and high levels of both messenger and ribosomal RNA mitochondrial tra nscripts are present after a few days of cold exposure. No changes in mitochondrial DNA abundance relative to total cellular DNA were observ ed in the liver of rats at any time during cold stress. It is conclude d that mitochondrial genome expression is specifically increased in th e liver of cold-exposed rats through different mechanisms, independent of changes in mitochondrial genome abundance.