Inositol signaling function

A second class of ligand-gated ion channels respond to intracellular ligands 3, 5 -cyclic guanosine mononucleotide (cGMP) in the vertebrate eye, cGMP and cAMP in olfactory neurons, and ATP and inositol 1,4,5-trisphosphate (IP3) in many cell types. These channels are composed of multiple subunits, each with six transmembrane helical domains. We discuss the signaling functions of these ion channels in Chapter 12. 

In the plant kingdom, the pathway of synthesis of 3- and 4-phosphorylated phosphoinositides has been described only in Spirodela polyrhiza L. [1]. If animal models of phosphoinositide metabolism are to be applied to plants, it is imperative to determine the route of synthesis of phosphoinositides in other members of the plant kingdom in which signaling functions for phosphoinositides and inositol phosphates have been implicated. Recently, we have rigorously identified 3- and 4-phosphorylated phosphoinositides in stomatal guard cells of Commelina communis L. [2]. In the present work we have set out to determine the metabolic route by which PtdIns(3,4)P and PtdIns(4,5)P synthesis occurs and to examine the metabolic relationship between 3- and 4-phosphoryrated lipids in stomatal guard cells. 

Depletion of ATP in the cells prevents maintenance of the membrane potential, inhibits the functioning of ion pumps, and attenuates cellular signal transduction (e.g., formation of second messengers such as inositol phos phates or cyclic AMP). A marked ATP depletion ultimately impairs the activ-itv of the cell and leads to ceil death. 

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