Effect of vip on the glycogen metabolism of human colon adenocarcinoma cells studied by ¹³C nuclear magnetic resonance spectroscopy

Metabolic pathways of glucose utilization have been investigated in a human colon adenocarcinoma cell line (HT29) using carbon‐13 Nuclear Magnetic Resonance spectroscopy. HT29 cells were adapted to grow on a polystyrene beaded microcarrier and were perfused when attached to the beads in a specially designed NMR cell. Abnormalities in carbohydrate metabolism already observed in several cancer cells were studied in HT29 cells fed with (I‐¹³C)‐enriched glucose. The cells were first perfused with a glucose‐free medium for 2 hr in order to deplete the intracellular store of glycogen, and they were subsequently perfused with a medium containing enriched glucose at an initial concentration of 5.5 mM. Sequential ¹³C‐NMR spectra, recorded at 100.5 MHz (5 min accumulation), show that HT29 cells were able to utilize glucose through the glycolytic pathway while storing glucose as glycogen (glucose was utilized at a rate of 3.9 μmol/mg protein/hr). The glycolytic activity determined by the amount of lactic acid produced was 4.6 μM/mg protein/hr, corresponding to the formation of 1.2 lactic acid per glucose molecule. Glycogen accumulation corresponded to 16 μg/mg of protein. Treatment of HT29 with 10 nM vasoactive intestinal peptide (VIP) induced a transient decrease in the level of labelled glycogen to 50% of the initial value. Control level was recovered 12 min after VIP loading.