Substrate Competition Studies Demonstrate Oxidative Metabolism of Glucose, Glutamate, Glutamine, Lactate and 3-Hydroxybutyrate in Cortical Astrocytes from Rat Brain

• Published in: Neurochemical research Vol. 37; no. 11; pp. 2613 - 2626
• Main Author: McKenna, Mary C.
• Format: Journal Article
• Language: English
• Published: Boston Springer US 01-11-2012; Springer Nature B.V
• Subjects: 3-Hydroxybutyric Acid - metabolism; Astrocytes; Astrocytes - metabolism; Biochemistry; Biomedical and Life Sciences; Biomedicine; Brain; Brain - cytology; Brain - metabolism; Cell Biology; Competition; Data processing; Energy metabolism; Energy resources; Glucose; Glucose - metabolism; Glutamic acid; Glutamic Acid - metabolism; Glutamine; Glutamine - metabolism; Lactic acid; Lactic Acid - metabolism; Neurochemistry; Neurology; Neurosciences; Original Paper; Oxidation; Oxidation-Reduction; Oxidative metabolism; Substrate Specificity; Tricarboxylic acid cycle; Energy metabolism; Lactate; 3-Hydroxybutyrate; Malate; Compartmentation; Astrocytes; Glucose; Glutamate; Substrate competition; Glutamine
• ISSN: 0364-3190; 1573-6903
• DOI: 10.1007/s11064-012-0901-3

It is well established that astrocytes can utilize many substrates to support oxidative energy metabolism; however, use of energy substrates in the presence of other substrates, as would occur in vivo, has not been systematically evaluated. Substrate competition studies were used to determine changes in the rates of
14
CO
2
production since little is known about the interaction of energy substrates in astrocytes. The rates of
14
CO
2
production from 1 mM D-[6-
14
C]glucose,
l
-[U-
14
C]glutamate,
l
-[U-
14
C]glutamine,
d
-3-hydroxy[3-
14
C]butyrate,
l
-[U-
14
C]lactate and
l
-[U-
14
C]malate by primary cultures of astrocytes from rat brain were determined to be 1.17 ± 0.19, 85.30 ± 12.25, 28.04 ± 2.84, 13.55 ± 4.56, 14.84 ± 2.40 and 5.20 ± 1.20 nmol/h/mg protein (mean ± SEM), respectively. The rate of
14
CO
2
production from glutamate oxidation was higher than that of the other substrates Addition of unlabeled glutamate significantly decreased the rates of
14
CO
2
production from all other substrates studied; however, glutamate oxidation was not altered by the addition of any of the other substrates. The rate of
14
CO
2
production of glutamine was decreased by glutamate, but not altered by other substrates. The rate of
14
CO
2
production from glucose was significantly decreased by the addition of unlabeled glutamate, glutamine or lactate, but not by 3-hydroxybutyrate or malate. Addition of unlabeled glucose did not significantly alter the
14
CO
2
production from any other substrate.
14
CO
2
production from lactate was decreased by the addition of unlabeled glutamine or glutamate and increased by addition of malate. The
14
CO
2
production from malate was decreased by the addition of unlabeled glutamate or lactate, but was not altered by the other substrates. The substrate utilization for oxidative energy metabolism in astrocytes is very different than the profile previously reported for synaptic terminals. These studies demonstrate the potential use of multiple substrates including glucose, glutamate, glutamine, lactate and 3-hydroxybutyrate as energy substrates for astrocytes. The data also provide evidence of interactions of substrates and multiple compartments of TCA cycle activity in cultured astrocytes.