Inositol uptake and metabolism in molluscan neuronal tissue

The uptake of myo-[3H]inositol into neurones from Lymnaea stagnalis has been demonstrated to be a sodium-dependent process, saturable with a Km of approximately 50 microM and shown to be linear with time for at least 120 min. The rate of transport of myo-inositol into the cell appears to influence directly its incorporation into neuronal lipids. Using anion-exchange high-performance liquid chromatography, we have demonstrated a high rate of breakdown of phosphatidylinositol 4,5-bisphosphate in Lymnaea nerve under basal conditions. Stimulation with carbamylcholine enhanced production of inositol 1-phosphate, inositol bisphosphate, inositol 1,4,5-trisphosphate, and inositol 1,3,4-trisphosphate. Formation of inositol tetrakisphosphate was not detected. Electrical stimulation also caused an increased formation of inositol phosphates. These results provide evidence for an active myo-inositol transport system in molluscan neurones and suggest that the hydrolysis of inositol lipids may play a role as an intracellular signalling system in this tissue.