Protein-mediated fatty acid uptake and intracellular fatty acid activation
are key steps in fatty acid metabolism in muscle.We have examined (a) the a
bundance of fatty acid translocase (FAT/CD36) mRNA (a fatty acid transporte
r) and long-chain acyl CoA synthetase (FACS1) mRNA in metabolically heterog
eneous muscles (soleus (SOL), red (RG) and white gastrocnemius (WG)), and (
b) whether FAT/CD36 and FACS1 mRNAs were coordinately upregulated in red (R
TA) and white tibialis muscles (WTA) that had been chronically stimulated f
or varying periods of time (0.25, 1, 6 and 24 h/day) for 7 days. FAT/CD36 m
RNA and FACS1 mRNA abundance were scaled with (a) the oxidative capacity of
muscle (SOL > RG > WG) (p < 0.05), (b) the rates of fatty acid oxidation i
n red and white muscles, and (c) fatty acid uptake by sarcolemmal vesicles,
derived from red and white muscles. In chronically stimulated muscles (RTA
and WTA), FAT/CD36 mRNA and FACS1 mRNA were up-regulated in relation to th
e quantity of muscle contractile activity (p < 0.05). FAT/CD36 mRNA and FAC
S1 mRNA up-regulation was highly correlated (r = 0.98). The coordinated exp
ression of FAT/CD36 and FACS is likely a functional adaptive response to fa
cilitate a greater rate of fatty acid activation in response to a greater r
ate of fatty acid transport, either among different types of muscles or in
muscles in which capacity for fatty acid metabolism has been enhanced.