A gas chromatographic (GC)/mass spectrometric method for studying myo-
inositol uptake by neurons in vitro is described. Cultured cortical neurons from fetuses of diploid and trisomy 16 mouse (animal model for
Down syndrome) were incubated with a physiological concentration of hexadeuterated myo-
inositol for 2-40 min. Washed cells were lysed and
scyllo-inositol (internal standard) was added to the intracellular material which contained labeled myo-
inositol taken up by the cells as well as the endogenous, unlabeled myo-
inositol. The samples were evaporated to dryness and the analytes were converted into
acetate derivatives. The components were separated by capillary GC, and the m/z 379 ion for labeled myo-
inositol and the m/z 373 ion for myo-
inositol and
scyllo-inositol generated by chemical ionization in an ion trap mass spectrometer were monitored. Quantitation of the
deuterium-labeled myo-
inositol taken up by the neuron along with endogenous myo-
inositol was achieved for 2-40 min of incubation. The labeled myo-
inositol uptake was linear for up to 20 min and was Na+ dependent in these neurons. This non-
radioisotope method was used to demonstrate a significant (40%) increase in the rate of myo-
inositol uptake by cortical neurons from the trisomy 16 mouse relative to control neurons. An increased myo-
inositol uptake is consistent with evidence that the myo-
inositol transporter gene is on both human chromosome 21 and mouse chromosome 16, and that myo-
inositol concentrations are elevated in cerebrospinal fluid from adult
Down syndrome individuals and brains from the fetal trisomy 16 mouse.