Table 2.
Comparison of the potential of exogenous substrates to maintain a high cellular ATP content in glucose-deprived astrocytes
| Substrate | EC50 | Number of oxidisable carbon atoms | EC50 x number of oxidisable carbon atoms | ATP content maintained by the highest substrate concentration applied | n | ||
|---|---|---|---|---|---|---|---|
| (µM) | (mM) | (mM) | (nmol/mg) | (% of initial) | |||
| Glucose | 554 ± 103 | 6 | 3.33 ± 0.62 | 3 | 27.8 ± 3.4 | 83 ± 10 | 9 |
| β-Hydroxybutyrate | 1166 ± 117*** | 4 | 4.66 ± 0.47 | 3 | 28.5 ± 2.3 | 87 ± 7 | 3 |
| Lactate | 954 ± 361** | 3 | 2.33 ± 0.90 | 3 | 29.3 ± 1.8 | 86 ± 5 | 6 |
| Pyruvate | 1010 ± 183* | 3 | 3.03 ± 0.55 | 3 | 28.2 ± 1.5 | 86 ± 5 | 3 |
| Acetate | 1196 ± 281*** | 2 | 2.39 ± 0.56 | 3 | 28.5 ± 1.3 | 87 ± 4 | 3 |
| Palmitate | 103 ± 13* | 16 | 1.64 ± 0.21** | 1 | 24.2 ± 2.5 | 76 ± 8 | 3 |
| Decanoate | 157 ± 83 | 10 | 1.57 ± 0.83** | 1 | 21.9 ± 2.3 | 69 ± 7 | 3 |
| Octanoate | 214 ± 56 | 8 | 1.71 ± 0.45** | 1 | 22.7 ± 2.9 | 71 ± 9 | 3 |
| Lysine | 1603 ± 70 ***, +++ | 6 | 9.62 ± 0.42 ***, +++ | 3 | 27.1 ± 4.2 | 77 ± 12 | 3 |
| Glutamate | 909 ± 44 +++ | 5 | 4.55 ± 0.22 +++ | 3 | 30.1 ± 3.7 | 85 ± 10 | 3 |
| Glutamine | 778 ± 15 +++ | 5 | 3.89 ± 0.08 +++ | 3 | 29.5 ± 3.1 | 84 ± 9 | 3 |
| Proline | 323 ± 7 | 5 | 1.62 ± 0.04** | 3 | 27.9 ± 3.1 | 79 ± 9 | 3 |
| Aspartate | 842 ± 27 +++ | 4 | 3.37 ± 0.11 +++ | 3 | 26.0 ± 5.1 | 74 ± 14 | 3 |
| Alanine | 1010 ± 29 *, +++ | 3 | 3.03 ± 0.09 +++ | 3 | 27.0 ± 2.1 | 76 ± 6 | 3 |
The initial concentrations of exogenous substrates that allowed half-maximal (EC50) maintenance of cellular ATP contents during a 24 h incubation was calculated for the total number of concentration-dependencies performed for the indicated substrates. In addition, the ATP contents determined for the given concentration of a substrate was included as specific content (nmol ATP/mg) and as percent of the initial ATP content at the onset of the 24 h incubation. The significance of differences (ANOVA with Bonferroni post hoc test) compared with the data obtained for glucose-treated cells is indicated by *p < 0.05, **p < 0.01 and ***p < 0.001. For amino acid-treated cells, the significance of differences compared to a proline-treatment is indicated by +++p < 0.001