Induction of Na+/myo-inositol co-transporter mRNA after rat cryogenic injury.

Myo-inositol is one of the major organic osmolytes in the brain. It is stored in the cells by the Na+/myo-inositol co-transporter (SMIT) which is regulated by extracellular osmolality. First, in order to confirm that local change of the osmolality induces alteration of the SMIT mRNA in brain, we examined change of SMIT mRNA of the animals with hypertonic NaCl application to the cortex. Application of hypertonic NaCl up-regulated the SMIT mRNA expression widely surrounding the application site. We next investigated the role of SMIT in brain during vasogenic edema, we examined expression of SMIT mRNA in the rat brain after cryogenic injury. The expression of SMIT mRNA was markedly increased 12 h after surgery and the induction of the mRNA extended to the entire cortex of the affected side. Up-regulated expression was found predominantly in the neurons in remote areas. The induction of SMIT mRNA was found until the 3rd day after surgery. These findings suggest that osmotic stress may spread over a wide area in the cortex in case of vasogenic edema produced by cryogenic injury and that the cells respond to this stress by increasing SMIT expression.