Myo-Inositol is a neutral cyclic polyol, abundant in mammalian tissues. It plays important roles; it is a precursor to phosphatidylinositols (PtdIns) and to the inositol phosphates (IP), which serve as second messengers and as key regulators of many cell functions. It can also serve as a compatible osmolyte during volume regulation in many tissues where cells are exposed to hyperosmotic conditions. Three members of the glucose transporter families are inositol transporters. Two (SMIT1 and SMIT2) couple myo-inositol transport with two Na+ ions. Unlike SMIT1, SMIT2 also transports D-chiro_inositol. The third transporter (HMIT), couples myo-inositol transport with a proton.