title: Calcium- and calmodulin-dependent phosphorylation of diphosphoinositide in acetylcholine receptor-rich membranes from electroplax of Narke japonica.
abstract: The phosphorylation of phosphoinositides in the acetylcholine receptor (AChR)-rich membranes from the electroplax of the electric fish Narke japonica has been examined. When the AChR-rich membranes were incubated with [gamma-32P]ATP, 32P was incorporated into only two inositol phospholipids, i.e., tri- and diphosphoinositide (TPI and DPI). Even after the alkali treatment of the membrane, AChR-rich membranes still showed a considerable DPI kinase activity upon addition of exogenous DPI. It is likely that the 32P-incorporation into these lipids was realized by the membrane-bound DPI kinase and phosphatidyl inositol (PI) kinase. Such a membrane-bound DPI kinase was activated by Ca2+ (greater than 10(-6) M), whereas the PI kinase appeared to be inhibited by Ca2+. The effect of Ca2+ on the DPI phosphorylation was further enhanced by the addition of ubiquitous Ca2+-dependent regulator protein calmodulin. Calmodulin antagonists such as chlorpromazine (CPZ), trifluoperazine (TFP), and N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7) inhibited the phosphorylation of DPI in the AChR-rich membranes. It is suggested that the small pool of TPI in the plasma membrane is replenished by such Ca2+- and calmodulin-dependent DPI kinase responding to the change in the intracellular Ca2+ level.
authors.forename: F
authors.initials: F
authors.lastname: Hayashi
authors.forename: T
authors.initials: T
authors.lastname: Amakawa
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002147:Calmodulin / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D002458:Cell Fractionation; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D004557:Electric Organ / Q000378:metabolism*; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols / Q000378:metabolism*; D010766:Phosphorylation; D010770:Phosphotransferases / Q000378:metabolism; D017853:Phosphotransferases (Alcohol Group Acceptor); D011950:Receptors, Cholinergic / Q000378:metabolism*; D014101:Torpedo / Q000378:metabolism*
chemical_list: D002147:Calmodulin; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols; D011950:Receptors, Cholinergic; C023687:diphosphoinositides; C018803:triphosphoinositide; D010770:Phosphotransferases; D017853:Phosphotransferases (Alcohol Group Acceptor); C020077:1-phosphatidylinositol-4-phosphate 5-kinase; D002118:Calcium