Hyperosmotic stress induces water diffusion out of the cell, resulting in cell shrinkage, and leading to DNA damage, cell cycle arrest, and cytoskeletal reorganization. A previous report showed that low concentrations of sorbitol (200 mM) could increase up to 25-fold the concentration of InsP(8) in animal cells. Here, we investigate the effect of sorbitol (200 mM) on the inositol 1,4,5-trisphosphate (InSP3) and inositol 1,3,4,5-tetrakisphosphate (InSP4) pathway. A 3- to 4-fold increase in InSP3 and InSP4 levels after sorbitol challenge was observed. It was prevented by the phospholipase C inhibitor U-73122 but was insensitive to the MAP kinase inhibitor U0126. We also observed an increase in the free intracellular [Ca2+] and the occurrence of Ca2+ oscillations in response to sorbitol. A hyperosmotic stress could therefore affect the levels of both hyperphosphorylated inositol phosphates and InSP3/InSP4-signalling molecules. (c) 2005 Elsevier Inc. All rights reserved.