NMR SPECTROSCOPIC STUDIES OF C-13 ACETATE AND C-13 GLUCOSE-METABOLISMIN NEOCORTICAL ASTROCYTES - EVIDENCE FOR MITOCHONDRIAL HETEROGENEITY

Neocortical astrocytes were incubated with C-13-labeled substrates to determine metabolic pathways. C-13 NMR spectroscopy was used to analyz e C-13 incorporation into glutamine and citrate from the different pre cursors [1-C-13]glucose or [2-C-13]acetate. When glucose was the label ing substrate, incorporation due to pyruvate carboxylation should be o bserved in the C-2 position in glutamine and the C-4 position in citra te. A large incorporation due to pyruvate carboxylation was observed i n glutamine in the C-2 and C-3 positions, but not in citrate. When ace tate was the precursor, the labeling ratios in the C-2/C-4 positions i n glutamine and in the equivalent positions in citrate were 0.27 and 0 .11, respectively. Moreover, acetate labeled lactate in the C-2 positi on much less than did glucose. Altogether, these observations led to t he conclusion that glutamine precursors and citrate are either produce d in different types of astrocytes or in different tricarboxylic acid cycles, situated in functionally different mitochondria in the same ce ll, and that in all likelihood pyruvate carboxylase is expressed diffe rently in these mitochondria.