Table 1.
Lactate 13C isotopologue content (%) | Modeled flux ratios (%) | ||||||||
---|---|---|---|---|---|---|---|---|---|
M | M1 | M2 | M3 |
(R1) |
(R2) |
(R3) |
(R4) |
Model error (%) | |
T47D | 50.02±0.13 a (50.08±0.08) | 3.20±0.06 a(3.29±0.11) | 45.89±0.19 a (45.89±0.19) | 0.89±0.04 a (0.74±0.02) | 8.9±0.5 a | 64±6 a | 3.9±0.1 a | 81±16 a | 0.42±0.09 |
MDA231 | 49.30±0.20 b (49.30±0.20) | 2.52±0.07 b (2.35±0.08) | 47.49±0.20 b (47.49±0.20) | 0.69±0.06 b (0.85±0.04) | 3.2±0.4 b | 40±380 a,b | 5.1±0.3 b | 100±0 a | 0.33±0.06 |
BoM | 49.04±0.17 b (49.15±0.08) | 3.28±0.14 a (3.23±0.24) | 46.59±0.33 a (46.59±0.33) | 1.09±0.05 a,c (1.03±0.05) | 5.5±0.7 c | 30±43 a,b | 5.9±0.3 b | 83±17 a | 0.37±0.19 |
LM | 49.08±0.05 b (49.25±0.13) | 3.03±0.05 a (3.18±0.13) | 46.60±0.12 a (46.60±0.12) | 1.29±0.05 c (0.97±0.07) | 6.2±0.2 a,c | 30±3 b | 5.4±0.4 b | 17±9 b | 0.73±0.22 |
Cells were equilibrated in 2-well Lab-Tek chambers for approximately 6.5 h with 5.5 mM [1,2-13C] glucose as the sole exogenous substrate. Basal respiration rate was assessed from 5 to 6.5 h, followed by 2 × 1 h incubations to determine the rates of glucose uptake, lactate and serine efflux, and 13C enrichment in lactate and serine. Respiration rates averaged 3.7±0.2, 25±4, 15±3, and 4.3±0.5 nmol O/min × mg for T47D, MDA-MB-231, BoM, and LM cells, respectively (mean ± SEM, n=6). 13C lactate labeling (mean ± SEM, n=6) is expressed as percent contribution of each isotopologue to total extracellular lactate (M, M1, M2, and M3 denote lactate with none, one, two, two, or three 13C atoms, respectively). Data in parentheses are simulated lactate labeling (mean ± SEM, n=6) from Model 1-optimized flux ratios R1, R2, R3, and R4. Model error was calculated as the sum of the absolute values of the difference between the measured and simulated M-M3 lactate. Within a column, means sharing common superscripts do not significantly differ