HPLC analysis of inositol phosphate isomers induced by neuroparsin in rectal epithelial cells of the african locust: Role of external calcium

Abstract Inositol 1-monophosphate (Ins (1) )P1), and together inositol 1,4-bisphosphate (Ins 1,4) P2) and inositol 4-monophosphate (Ins (4) P1) were rapidly (5s) generated in the presence of low concentrations of neuroparsin (NP), likely by hydrolysis of phosphatidylinositol monophosphate (PIP) and phosphatidylinositol (PI) substrates with a phospholipase C (PLC). High concentrations of NP activated another membrane effector which hydrolyzed phosphatidylinositol 4,5-bisphosphate (PIP2) and produced inositol 1,4,5-trisphosphate which is either dephosphorylated in Ins (4) P1 or phosphorylated in inositol 1,3,4,5-tetrakisphosphate, then rapidly dephosphorylated in inositol 1,3,4-trisphosphate and finally in Ins (1) P1. Both PLC are Ca 2+ -dependent. Their existence possibly reflects the involvement of two distinct transduction mechanisms for the antidiuretic signal of NP according to its concentration. Beyond a previous action of NP demonstrated on the opening of L-type Ca 2+ channels, experiments show the early participation of other types of Ca 2+ channels.