Role of pyruvate carboxylation in the energy-linked regulation of pool sizes of tricarboxylic acid-cycle intermediates in the myocardium.

The increase in the metabolite pool size of the tricarboxylic acid cycle in the isolated perfused rat heart after a decrease in the ATP consumption by KCl-induced arrest was used to study the anaplerotic mechanisms. During net anaplerosis the label incorporation into the tricarboxylic acid-cycle intermediates from [1-14C]pyruvate increased and occurred mainly by pathways not involving prior release of the label to CO2. A method for determination of the specific radioactivity of mitochondrial pyruvate was devised, and the results corroborated the notion that tissue alanine can be used as an indicator of the specific radioactivity of intracellular pyruvate.