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.
Department of Biochemistry and Molecular Biology, University of Bergen, Bergen, Norway.
Hege
H
Iversen
Edvin
E
Fuglebakk
Holm
H
Holmsen
Miriam H
MH
Fukami
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