Table 3

GAA and Cr synthesis experiments in rat astrocytes

Concentration of [15N2]Arg and [13C2,15N]Gly

in the medium (mmol/L)

[15N2]Arg in the cells

(nmol/mg protein)

Arg in the cells

(nmol/mg protein)

[15N2]Arg/Arg


0

1.8 ± 1.1

172.0 ± 78.2

0.01 ± 0.00

5

137.9 ± 71.6 NS

145.5 ± 73.4

1.12 ± 0.52

10

504.0 ± 390.0 *

178.6 ± 137.9

3.43 ± 1.66

15

957.4 ± 500.45 **

215.5 ± 132.5

6.74 ± 4.72


[13C2,15N]Gly in the cells

(nmol/mg protein)

Gly in the cells

(nmol/mg protein)

[13C2,15N]Gly/Gly


0

2.8 ± 0.9

365.7 ± 43.2

0.01 ± 0.00

5

1003.8 ± 1083.3 NS

696.3 ± 604.2

1.28 ± 0.49

10

2205.5 ± 2382.0 *

893.8 ± 958.4

2.53 ± 0.22

15

3213.9 ± 2482.9 *

744.8 ± 512.7

4.43 ± 0.85


[13C215N3]GAA in the cells

(nmol/mg protein)

GAA in the cells

(nmol/mg protein)

[13C215N3]GAA/GAA


0

0.25 ± 0.09

1.46 ± 1.46

0.29 ± 0.14

5

10.34 ± 7.90 *

2.37 ± 2.23

4.47 ± 3.97

10

17.18 ± 13.36 *

1.88 ± 1.87

13.30 ± 14.32

15

21.59 ± 15.00 **

1.64 ± 1.11

18.18 ± 17.96


[13C215N3]Cr in the cells

(nmol/mg protein)

Cr in the cells

(nmol/mg protein)

[13C215N3]Cr/Cr


0

0.10 ± 0.05

100.4 ± 118.7

0.00 ± 0.00

5

12.13 ± 12.64 *

86.53 ± 71.65

0.12 ± 0.04

10

10.88 ± 8.48 **

59.48 ± 23.72

0.17 ± 0.08

15

11.00 ± 6.85 **

48.54 ± 10.58

0.21 ± 0.09


Intracellular concentrations of Gly, [13C2,15N]Gly, Arg, [15N2]Arg, GAA, [1,2-13C2,15N3]GAA, Cr and [1,2-13C2,15N3]Cr after 24 h in vitro incubation with [15N2]Arg and [13C2,15N]Gly under different concentrations of labeled precursors in the medium: no labeled precursors (0), 5, 10 and 15 mmol/L. The statistical significance of the differences between intracellular concentrations of labeled and unlabeled compounds was assessed by paired Student's t-test: NS not significant, * p < 0.05, ** p < 0.01. The concentrations of [13C2,15N]Gly and [15N2]Arg were significantly higher than those of Gly and Arg (except for cells incubated with [15N2]Arg mmol/L), showing that the labeled precursors are highly available into the cells for Cr synthesis. [13C2,15N3]GAA concentrations were also significantly higher than those of GAA, whereas [13C2,15N3]Cr levels remained significantly lower than those of Cr. The ratios express the relative intracellular availability of labeled and unlabeled forms (right column).

Carducci et al. BMC Neuroscience 2012 13:41   doi:10.1186/1471-2202-13-41

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