Regulation of Myo-Inositol Homeostasis in Differentiated Human NT2-N Neurons

We have investigated the possible role of second messengers on inositol homeostasis in NT2-N cells, human central nervous system neurons obtained by terminal differentiation of teratocarcinoma precursors. Uptake of inositol into NT2-N neurons was inhibited ∼10% by protein kinase C (PKC) activation but was unaffected by either the presence of cyclic nucleotide analogs or changes in the intracellular concentration of Ca2+. Efflux of inositol from NT2-N neurons was enhanced in hypotonic buffer but virtually eliminated by inclusion of the Cl− channel blocker 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid, a result which indicates the involvement of a volume-sensitive organic osmolyte-anion channel. Volume-sensitive inositol efflux was stimulated ∼30% following activation of PKC or elevation of the cytosolic Ca2+ concentration but was unaffected by protein kinase A activation. These results suggest that whereas inositol uptake into NT2-N neurons is relatively refractory to regulation, volume-sensitive inositol efflux may be significantly affected by intracellular signaling events.