Regulation of myo‐inositol in tilapia (Oreochromis mossambicus) brain during hyperosmotic stress

Abstract

Myo‐inositol (MI) is a compatible organic osmolyte that is accumulated in cells exposed to hyperosmotic stress via various biochemical pathways. We and others have shown that the de novo biosynthetic pathway, which synthesizes MI from glucose‐6‐phosphate, is especially important for osmoregulation in Mozambique tilapia (Oreochromis mossambicus). Additional pathways of MI accumulation utilize membrane transporters, such as sodium/myo‐inositol cotransporter and proton/myo‐inositol cotransporter, to move exogenous MI into the cell. In order to investigate mechanisms of the osmotic stress response, an immortalized cell line was established from primary explant cultures of tilapia brain tissue. To validate this cell line, we studied the effects of acute and chronic osmotic stress on MI regulation in tilapia brain. Myo‐inositol phosphate synthase (MIPS) mRNA expression data were compared from in vitro (tilapia brain cell line) and in vivo (tilapia whole brain) approaches. MIPS, which is one of two key enzymes of the biosynthetic pathway, was highly upregulated both in vivo and in vitro after acute exposure to osmotic stress (25ppt seawater or 700mOsm medium). Blood plasma osmolality, sodium, chloride, and potassium concentrations were also measured in vivo to complement mRNA expression data and relate changes in osmotic blood chemistry to changes in cell culture medium. Supported by NSF grant IOS‐1049780.