Fig. 9.

Metabolite abundance and isotopomers in response to hyperglycaemia. a Relative abundance of the indicated metabolites in INS-1 cells cultured at 25 mM expressed as a fraction of that in INS-1 cells cultured at 5 mM glucose. All cells were challenged with 20 mM [U-¹³C]-glucose for 30 min. DHAP, dihydroxyacetone phosphate. PEP, phosphenolpyruvate. Hexitol (sorbitol/mannitol). Data are mean ± s.e.m. (n = 15 independent samples except for hexitol and succinate where n = 9). One-way analysis of variance with Holm–Sidak’s multiple comparisons test, *p < 0.05, **p < 0.01. b, c Mass isotopomer distributions (MIDs) of the indicated metabolites in INS-1 cells cultured at 5 mM glucose (white bars) or 25 mM glucose (black bars) and then challenged with 20 mM [U-¹³C]-glucose for 30 min (b) or 60 min (c). Data are derived from a subset of that used in Fig. 8. Mean ± s.e.m.; n = 4 independent samples. ‘M + n’ (where ‘M’ is the m/z of the unlabelled ion) and ‘n’ indicates the number of ¹³C atoms in that isotopomer. The data for each isotopomer are expressed as a fraction of the total labelled isotopomers for that metabolite. Since pyruvate and acetyl-CoA contain three and two carbons, respectively, MIDs of +3 are indicative of carbon entry into the TCA through carboxylation of pyruvate, +2, +4 and +6 are indicative of entry through acetyl-CoA (multiple cycles), while +5 indicates that it is derived from both pyruvate carboxylation and acetyl-CoA