Sodium/Myo Inositol Cotransporter (SMIT)

Cerebrospinal fluid levels are higher than those in the blood due to a combination of de novo synthesis in brain capillary pericytes, concentrative uptake at the choroid plexus, and limited transport capacity across the blood-brain barrier. The SLC5A3 protein is number 3 of the solute carrier family 5 and was initially designated SMIT.The predicted 718-amino acid protein is highly homologous to the product of the canine SLC5A3 gene. The authors found expression of SLC5A3 in many tissues, including brain. They commented that the inability of a trisomic 21 cell to downregulate expression of 3 copies of this osmoregulatory gene could result in increased flux of both myoinositol and sodium ion across the plasma membrane. The potential consequences include perturbations in the cell membrane potential and tissue osmolyte levels.