Glucose Cycling in Beta Cell Lines

Glucose cycling in βTC3 and INS1-832/13 cells was measured using our previously defined approach (8 (link)). Briefly, 8 to 10 million cells were incubated for 24 or 72 h at 37 °C in RPMI 1640 medium containing 5 mM or 11 mM glucose in 10-cm dishes. Cells were incubated in either naturally labeled glucose or [1,2,3,4,5,6,6-²H₇]glucose (Cambridge Isotope Laboratories; Cat no. DLM-2062). Following the 24- or 72-h incubation, the supernatant was collected for glucose derivatization and GC-MS analysis (see Extraction of metabolites and GC-MS analyses). The glucose MID was quantified, and absolute glucose concentration was determined through comparison to a standard curve. Glucose cycling and glucose uptake rates were calculated as described previously (8 (link)).