OSMOTIC REGULATION OF MYOINOSITOL UPTAKE IN PRIMARY ASTROCYTE CULTURES

Uptake of myo-inositol by astrocytes in hypertonic medium (440 mosm/kg H2O) was increased near 3-fold after incubation for 24 hours, which c ontinued for 72 hours, as compared with the uptake by cells cultured i n isotonic medium (38 nmoles/mg protein). myo-Inositol uptake by astro cytes cultured in hypotonic medium (180 mosm/kg H2O) for periods up to 72 hours was reduced by 74% to 8 to 10 nmoles/mg protein. Astrocytes incubated in either hypotonic or hypertonic medium for 24 hours and th en placed in isotonic medium reversed the initial down- or up-regulati on of uptake. Activation of chronic RVD and RVI correlates with regula tion of myoinositol uptake. A 30 to 40 mosm/kg H2O deviation from phys iological osmolality can influence myo-inositol homeostasis. The intra cellular content of myo-inositol in astrocytes in isotonic medium was 25.6 +/- 1.3 mu g/mg protein (28 mM). This level of myo-inositol is su fficient for this compound to function as an osmoregulator in primary astrocytes and it is likely to contribute to the maintenance of brain volume.