Measure of carbon and nitrogen stable isotope ratios in cultured cells

We report the measurement of the natural isotope ratios of nitrogen and carbon in subcellular volumes of individual cells among a population of cultured cells using a multi-isotope imaging mass spectrometer (MIMS), [MIMS is the prototype of the NanoSIMS 50, Cameca, France.] We also measured the nitrogen and carbon isotope ratio in cells after they had been cultured in media enriched with the amino acid glycine labeled with either C-13 or N-15. The results demonstrate that C-13/C-12 and N-15/N-14 isotope ratios can be measured directly on a subcellular scale. This opens the way for the use of stable isotopes, in particular N-15, as labels to measure the intracellular turnover of biomolecules. Such a capability should help resolve a wide range of biomedical problems. (C) 2004 American Society for Mass Spectrometry.