Hyperosmotic stress stimulates inositol 1,4,5-trisphosphate and inositol 1,3,4,5-tetrakisphosphate formation independently of bis-diphosphoinositol tetrakisphosphate modulation.

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 (200mM) could increase up to 25-fold the concentration of InsP(8) in animal cells. Here, we investigate the effect of sorbitol (200mM) on the inositol 1,4,5-trisphosphate (InsP(3)) and inositol 1,3,4,5-tetrakisphosphate (InsP(4)) pathway. A 3- to 4-fold increase in InsP(3) and InsP(4) 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 [Ca(2+)] and the occurrence of Ca(2+) oscillations in response to sorbitol. A hyperosmotic stress could therefore affect the levels of both hyperphosphorylated inositol phosphates and InsP(3)/InsP(4)-signalling molecules.