Analysis of Cellular Phosphoinositides and Phosphoinositols by Extraction and Simple Analytical Proc

Part A. Biosynthesis and Extraction of Phosphoinositides and Phosphoinositols The minor inositol-containing membrane phospholipids, the phosphoinositides, play a central role in cell signal transduction. Activation of a hormone-sensitive phospholipase C (phosphoinositidase C) results in the rapid catabolism of the polyphosphoinositides to form the two second messengers inositol 1,4,5-trisphosphate (Ins(l,4,5)P 3 ), a water soluble phosphoinositol that promotes the release of Ca 2+ from intracellular stores, and diacylglycerol (DG), which remains in the plasma membrane and activates protein kinase C ( 1 – 3 ). See Fig. 1 for a summary of the pathways.   Fig. 1.  Metabolic pathways activated as a consequence of phosphoinositidase C action. In Panel A major metabolic pathways activated by phosphoinositidase C action on PtdIns(4,5)P 2 are shown with solid arrows. Some of the additional pathways that may be activated are shown by broken arrows Abbreviations: Ptdlns: phosphatidylinositol; PtdIns4P. phosphatidylinositol 4-phosphate; PtdIns(4,5)P 2 phosphatidylinositol 4,5-bisphosphate; DG: diacylglycerol; PtdOH: phosphatidic acid; CDP-DG: CDP-diacylglycerol; Ins: Inositol. For phosphoinositols, abbreviations are in the form Ins( x,y,z )P n where x, y , and z refer to the positions of the phosphate groups on the myo-inositol ring and n refers to the total number of phosphates. Panel B is a simplified outline of the metabolic pathways in (A) to show alternative abbreviations. PI: phosphatidylinositol, PIP: phosphatidyl-inositol phosphate; PIP 2 , phosphatidylinositol bisphosphate; DG, PtdOH, CDP-DG and Ins as above. Phosphoinositols are referred to as IP n where n refers to the number of phosphates on the inositol ring In both panels, sites of Li *+ inhibition are also shown.