Differentiated human NT2-N neurons possess a high intracellular content ofmyo-inositol

myo-Inositol plays a key role in signal transduction and osmotic regulation events in the CNS. Despite the known high concentrations of inositol in th e human CNS, relatively little is known about its distribution within the d ifferent cell types. In this report, inositol homeostasis was studied in NT 2-N cells, a unique cell culture model of human CNS neurons. Differentiatio n of precursor NT2 teratocarcinoma cells into NT2-N neurons by means of ret inoic acid treatment resulted in an increase in inositol concentration from 24 to 195 nmol/mg of protein. After measurement of intracellular water spa ces, inositol concentrations of 1,6 and 17.4 mM were calculated for NT2 and NT2-N cells, respectively. The high concentrations of inositol in NT2-N ne urons could be explained by (1) an increased uptake of inositol (3.7 vs. 1. 6 nmol/mg of protein/h, for NT2-N and NT2 cells, respectively) and (2) a de creased efflux of inositol (1.7%/h for NT2-N neurons vs. 9.0%/h for NT2 cel ls). Activity of inositol synthase, which mediates de novo synthesis of ino sitol, was not detected in either cell type. The observation that CNS neuro ns maintain a high intracellular concentration of inositol may be relevant to the regulation of both phosphoinositide signaling and osmotic stress eve nts in the CNS.