| In a comparison between the control limbs of 6 and 24 month old rats , the mRNA levels of UCP 3 , heart type fatty acid binding protein ( HFABP ) , and glucose transporter 4 ( GLUT 4 ) were considerably lower in the gastrocnemius muscles of the older rats , whereas no significant differences in the mRNA levels of those genes as well as UCP 2 and cytochrome oxidase subunit 4 ( COX 4 ) were observed in the soleus muscles of young and old rats . ^^^ These results indicate that the effects of aging and denervation on the gene expression of UCPs , HFABP , GLUT 4 , and COX 4 are different between the muscle types . ^^^ |