Interaction of octanoate with branched-chain 2-oxo acid oxidation in rat and human muscle in vitro.

Acetate and butanoate inhibited and hexanoate and octanoate increased the 14CO2 production from 0.1 mM [1-14C]-labelled 2-oxoisocaproate (KIC) and 2-oxoisovalerate (KIV) in rat hemidiaphragms. Octanoate increased KIC and KIV oxidation in rat soleus muscle, too, inhibited it in human skeletal muscle and had a divergent effect in rat and human heart slices. In rat hemidiaphragms octanoate primarily affected the process of oxidative decarboxylation. No effect was found on transamination rates of branched-chain amino acids and on the CO2 production beyond alpha-decarboxylation. The reverse transamination of branched-chain 2-oxo acids and their incorporation into protein decreased in the presence of octanoate. Octanoate had no effect on KIC and KIV oxidation at higher 2-oxo acid concentrations and in hemidiaphragms from 3-day-starved rats. The observed interactions are discussed and related to regulatory mechanisms, which are known to affect the branched-chain 2-oxo acid dehydrogenase complex.