Identification of minor metabolites of phospholipid signal molecules in [(32)P]P(i)-labelled platelets.
Incubation of blood platelets with (32)P-labelled inorganic phosphate for 60 min leads to incorporation of radioisotope mainly into phosphatidylinositol (PI), phosphatidylinositol-4-phosphate (PIP) and phosphatidyl-4,5-bisphosphate (PIP(2)) in resting platelets and into phosphatidic acid (PA) in activated platelets. Small amounts of other important phosphoinositide isomers also become labelled following platelet activation, among them the 3-phosphorylated derivatives. In addition, several other faintly labelled spots are visible on TLC separations. Three of these lipids have now been identified as lysophosphatidylinositol (lysoPI), lysophosphatidic acid (lysoPA) and CDP-diacylglcerol (CDP-DAG).[(32)P]LysoPI was present in resting and activated platelets, whereas [(32)P]lysoPA and [(32)P]CDP-DAG were observed only upon platelet activation. The phosphoinositide cycle turns over without accumulation of [(32)P]PA and [(32)P]CDP-DAG in resting platelets. A large increase (as much as 40-fold) in the steady-state level of [(32)P]PA is seen in thrombin-activated platelets. A slight increase in the steady-state levels of [(32)P]CDP-DAG is accompanied by a similar increase in [(32)P]PI and larger increases in [(32)P]PIP and [(32)P]PIP(2) (about 50%), which is indicative of a general increase in flux in the PPI cycle. Elevation of CDP-DAG levels is probably only a reflection of increased flux, whereas lysoPA and lysoPI have been reported to have diverse signalling functions in various cells.
Iversen
Hege
H
Department of Biochemistry and Molecular Biology, University of Bergen, Bergen, Norway.
Fuglebakk
Edvin
E
Holmsen
Holm
H
Fukami
Miriam H
MH
D001792:Blood Platelets / Q000378:metabolism*; D002855:Chromatography, Thin Layer; D003567:Cytidine Diphosphate Diglycerides / Q000032:analysis / Q000378:metabolism; D006801:Humans; D008246:Lysophospholipids / Q000032:analysis / Q000378:metabolism; D010710:Phosphates; D010716:Phosphatidylinositols / Q000378:metabolism*; D010759:Phosphorus Isotopes; D015539:Platelet Activation; D011849:Radioactive Tracers; D015290:Second Messenger Systems; D013917:Thrombin / Q000494:pharmacology
D003567:Cytidine Diphosphate Diglycerides; D008246:Lysophospholipids; D010710:Phosphates; D010716:Phosphatidylinositols; D010759:Phosphorus Isotopes; D011849:Radioactive Tracers; C025449:lysophosphatidylinositol; D013917:Thrombin