T3 increases mitochondrial ATP production in oxidative muscle despite increased expression of UCP2 and -3

Date: 
01-26-2001

Triiodothyronine (T3) increases O2 and nutrient flux through mitochondria (Mito)
of many tissues, but it is unclear whether ATP synthesis is
increased, particularly in different types of skeletal muscle,
because variable changes in uncoupling proteins (UCP) and
enzymes have been reported. Thus Mito ATP production was
measured in oxidative and glycolytic muscles, as well as in
liver and heart, in rats administered T3 for 14 days. Relative
to saline-treated controls, T3 rats had 80, 168, and 62%
higher ATP production in soleus muscle, liver, and heart,
respectively, as well as higher activities of citrate synthase
(CS; 63, 90, 25%) and cytochrome c oxidase (COX; 119, 225,
52%) in the same tissues (all P , 0.01). In plantaris muscle
of T3 rats, CS was only slightly higher (17%, P , 0.05) than
in controls, and ATP production and COX were unaffected.
mRNA levels of COX I and III were 33 and 47% higher in
soleus of T3 rats (P , 0.01), but there were no differences in
plantaris. In contrast, UCP2 and -3 mRNAs were 2.5- to
14-fold higher, and protein levels were 3- to 10-fold higher in
both plantaris and soleus of the T3 group. We conclude that
T3 increases oxidative enzymes and Mito ATP production and
Mito-encoded transcripts in oxidative but not glycolytic rodent
tissues. Despite large increases in UCP expression, ATP
production was enhanced in oxidative tissues and maintained
in glycolytic muscle of hyperthyroid rats.

Read the full article.  Click here.

Authors: 
KEVIN R. SHORT, JONAS NYGREN, ROCCO BARAZZONI, JAMES LEVINE, AND K. SREEKUMARAN NAIR