Effect of dibutyryl cyclic AMP on the kinetics of myo-inositol transport in cultured astrocytes

Dibutyryl cyclic AMP (dBcAMP) is known to induce maturation and differentia tion in astrocytes. As myo-inositol is an important osmoregulator in astroc ytes, we examined the effects of maturation and biochemical differentiation on the kinetic properties of myo-inositol transport. Treatment of astrocyt es with dBcAMP significantly decreased the V-max of myo-inositol uptake, bu t the effect on K, was not significant. The myo-inositol content of astrocy tes was significantly decreased in cells treated for 5 days with dBcAMP as compared with untreated controls. Maximum suppression of myo-inositol uptak e occurred 7 days after exposure of astrocytes to dBcAMP; this was graduall y reversible when dBcAMP was removed from the medium. After exposure to hyp ertonic medium for 6 h, mRNA expression of the myo-inositol co-transporter was diminished by similar to 36% in astrocytes treated with dBcAMP as compa red with untreated cells. It appears that myo-inositol transporters in astr ocytes treated with dBcAMP are either decreased in number or inactivated du ring maturation and differentiation, suggesting that the stage of different iation and biochemical maturation of astrocytes is an important factor in o smoregulation.