Elimination of the settling artifact in the nuclear magnetic resonance spectroscopy of living cells.

Nuclear magnetic resonance spectroscopy has become a powerful tool for metabolic investigations on living cell suspensions. However, unless mechanical means are used to maintain the cells in dispersion, settling occurs during the NMR experiment. Because high packed-cell volumes are generally used to produce maximum NMR signals, settling may be inapparent to the eye, leading to unrecognized artifactual changes in NMR spectra. Such artifacts include time-dependent loss of signal intensity when the sample volume approximates the sensitive volume of the NMR probe, and time-dependent increase in signal intensity when the sample volume exceeds the sensitive volume. Through the addition of the polysaccharide arabinogalactan, increasing the buoyant density of the suspending medium to approach that of the cells, we have eliminated cell settling and improved the quality of 31P NMR spectra of human erythrocytes.