Formation of Inositol Polyphosphates in Cultured Adrenal Chromaffin Cells
In a variety of cell types, the rapid hydrolysis of phosphoinositides to 1,2-diacylglycerol and inositol 1,4,5-trisphosphate (Ins (1,4,5) P3) plays an important role in transmembrane signalling (Nishizuka, 1984). Diacylglycerol acts through stimulating protein kinase C, whereas Ins (1,4,5) P3 releases calcium from intracellular storage sites (Berridge and Irvine, 1984). It has been reported that these second messengers are generated by a signal transduction process comprising three main component s: a receptor, a GTP-binding protein and phospholipase C (Berridge and Irvine, 1984). However, it still possible that changes in cytosolic calcium concentration have physiologically relevant effects on phospholipase C, and it remains controversial as to whether the activation of phospholipase C is a consequence or forerunner of the rise in intracellular calcium concentration. Furthermore, details of some of the metabolic pathways linking them have been elucidated. The metabolism of inositol pentakisphosphate (InsP5) and inositol hexakisphosphate (InsP6) occurs through pathways which are separate from the agonist-sensitive pathways and is not clear in intact cells. Therefore, InsP5 and InsP6 are generally assumed to have a “housekeeping” function rather than being acute second messengers (Berridge and Irvine, 1989).
KeywordsChromaffin Cell Inositol Phosphate Inositol Trisphosphate Adrenal Chromaffin Cell Inositol Polyphosphates
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