Open AccessTurnover of the phosphomonoester groups of polyphospoinositol lipids in unstimulated human platelets
Author(s) -
VERHOEVEN Adrie J. M.,
TYSNES OleBjørn,
AARBAKKE Grethe M.,
COOK Carol A.,
HOLMSEN Holm
Publication year - 1987
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1987.tb13475.x
Subject(s) - extracellular , phosphatidylinositol , platelet , biochemistry , metabolism , phosphate , adenosine triphosphate , pi , chemistry , biology , phosphorylation , immunology
The metabolic activity of the polyphosphoinositol lipids in unstimulated human platelets was studied by shortterm labelling with [ 32 P]P i by replacement [ 32 P]P i from pre‐labelled platelets with unlabelled phosphate, and by depriving the cells of metabolic ATP.1 Under short‐term labelling conditions, the 4‐ and 5‐phosphate groups of phosphatidylinositol 4‐phosphate (PtdIns4 P ) and phosphatidylinositol 4,5‐bisphosphate [PtdIns(4,5) P 2 ] had the same specific 32 P radioactivity as the γ‐phosphate of metabolic ATP. The specific 32 P readiactivity of the 1‐phosphates of phosphatidylinositol, PtdIns4 P and PtdIns(4,5) P 2 was similar, but only 4–13% compared to that of the ATP‐γ‐phosphate. 2 When [ 32 P]P i pre‐labelled platelets were incubated with up to 25 mM of unlabelled phosphate, the displacement of the 32 P label from PtdIns4 P , PtdIns(4,5) P 2 and metabolic ATP followed similar kinetics. 3 Inhibition of ATP regeneration in platelets pre‐labelled with [ 32 P]P i resulted in a rapid fall in metabolic ATP with a much slower fall in [ 32 P]PtdIns(4,5) P 2 , whereas [ 32 P]PtdIns4 P increased initially. However, ATP turnover was not abolished, as indicated by the marked (25% of the control) incorporation of extracellular [ 32 P]P i into PtdIns4 P and PtdIns(4,5) P 2 in metabolically inhibited platelets. This low phosphate turnove may explain the relative resistance of PtdIns4 P and PtdIns(4,5) P 2 to metablic inhibition. We conclude that PtdIns4 P and PtdIns(4,5) P 2 are present as a single metabolic pool in human platelets. Turnover of the 4‐ and 5‐phosphates of PtdIns4 P and PtdIns(4,5) P 2 in unstimulated platelets is as rapid as that of the γ‐phosphate of metabolic ATP, and accounts for about 7% of basal ATP consumption.