Total cellular putrescine levels (nmol/mg protein); [13C
]ornithine decarboxylation to [13C
]putrescine, expressed as atom percent excess (APE); and levels of putrescine released into the medium, expressed as a percentage of the total cellular putrescine pool. Labeling of cellular [13C4]putrescine with [13C5]ornithine (100 μM) was a 30 min. incubation. The intracellular ornithine pool was > 97% [13C5]labeled in all cells. Efflux of putrescine was measured using a 1.5 hr incubation. Drug concentrations were 10 μM (ibuprofen) and 50 μM (PPI-1011) for 48 hr. prior to the experiment. N = 6. Mean ± SEM. *, p < 0.01 vs. CHO; #, p < 0.01 vs. untreated NRel.