ABSTRACT
Inositol phosphatides serve as precursors of two types of cellular messengers or mediators; inositol phosphates and diacylglycerol. Plasma membrane phosphatidylinositol can be further phosphorylated to form phosphatidylinositol-4-phosphate and phosphatidylinositol-4,5-bisphosphate. Evidence has been given in favor of the existence of a novel phosphoinositide containing four phosphates, phosphatidylinositol trisphosphate. The hydrolysis of inositol phosphatides occurs mainly in response to calcium-mobilizing agonists that have an effect on both internal and external calcium pools. Infusion of inositol pentakis- and hexakisphosphate into a discrete brain stem nucleus implicated in cardiovascular regulation has been shown to result in changes in heart rate and blood pressure. The pathways for the synthesis of inositol pentakis- and hexakisphosphate have been shown to be independent of the other inositol phosphates. Most of the phosphatidylinositol, however, is in the endoplasmic reticulum and a small percent is at the plasma membrane.
