Metabolism of 3-(13)C-malate in primary cultures of mouse astrocytes

Abstract

Malate, specifically labeled with carbon 13 on C(3), was synthesized by chemical means and used to study malate metabolism by primary cultures of mouse cortical astrocytes. 3-(13)C-Malate in combination with glucose as well as 3-(13)C-malate alone were used as substrates; the effect of 3-nitropropionic acid, an inhibitor of succinate dehydrogenase and fumarase was also examined. The consumption of malate was only 0.26 micromol/mg of protein, approx. 25-fold lower than the consumption of glucose. Besides lactate, glutamine and fumarate were the two major metabolites released to the medium. Very low and similar levels of isotopic enrichment were detected on C(2) and C(3) of lactate; glutamine was labeled on C(2) and C(3) to a similar extent as well and labeling on C(4) was only detected when glucose was not added. These labeling studies suggest that cytosolic malic enzyme is not active in primary astrocytes and support the occurrence of pyruvate recycling in astrocytes.