Fig. 5.

Comparing extracellular and intracellular M3 fraction of pyruvate and lactate. a Extracellular enrichments closely mirrored intracellular enrichments for both FM and EM experiments. Unlabelled lactate was present in the initial culture medium; thus, extracellular lactate was less enriched than intracellular lactate. The differences, however, were not inflated by a 10-fold larger extracellular pool size in EM (10 vs. 1 mM). b Reversibility ratios of lactate exchange and the calculated SSRs (residual sum of squares) for FM and EM experiments. χ ²(DoF = 1, p = 0.05) of 3.84 was used to determine the ratios’ 95 % confidence intervals. A reaction can be treated as fully reversible or irreversible if the calculated reversibility ratio is ≥25 or ≤0.05, respectively