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Formation of lysophosphatidylinositol in platelets stimulated with thrombin or ionophore A23187. 1982

M M Billah, and E G Lapetina

In stimulated platelets phosphatidylinositol is degraded by a phosphatidylinositol-specific phospholipase C to 1,2-diacylglycerol which is then phosphorylated to phosphatidic acid. Thrombin stimulation of horse and human platelets prelabeled with [32P]orthophosphate induces the formation of [32P]lysophosphatidylinositol, suggesting that phosphatidylinositol is also degraded by a phospholipase of A type activity. Stimulation of platelets prelabeled with 32P or with 32P plus [3H]inositol produces a lysophosphatidylinositol which has a 32P-specific activity and a 3H/32P ratio which has a 32P-specific activity and a 3H/32P ratio identical with those of phosphatidylinositol. These results suggest that the lysophosphatidylinositol derives from phosphatidylinositol. Thrombin stimulation of platelets double label with 32P and [3H]arachidonate induces loss of [3H]arachidonate from phosphatidylinositol and formation of [32P]lysophosphatidylinositol, suggesting the involvement of a phospholipase A2 activity. Ionophore A23187 also induces the formation of lysophosphatidylinositol in horse and human platelets. With either stimulus, [32P]lysophosphatidylinositol appears within seconds after stimulation and parallels the loss of [3H]arachidonic acid from phosphatidylinositol. The lysophosphatidylinositol produced by thrombin or by ionophore A23187 represents 40% of the degraded phosphatidylinositol as assessed by lipid phosphorus. Quinacrine, which inhibits the liberation of arachidonic acid from phospholipids, also blocks the formation of lysophosphatidylinositol. The results presented here indicate that phosphatidylinositol is degraded by both phospholipases, C and A2, in stimulated platelets.

UI MeSH Term Description Entries
D007294 Inositol An isomer of glucose that has traditionally been considered to be a B vitamin although it has an uncertain status as a vitamin and a deficiency syndrome has not been identified in man. (From Martindale, The Extra Pharmacopoeia, 30th ed, p1379) Inositol phospholipids are important in signal transduction. Myoinositol,Chiro-Inositol,Mesoinositol,Chiro Inositol
D007700 Kinetics The rate dynamics in chemical or physical systems.
D008246 Lysophospholipids Derivatives of PHOSPHATIDIC ACIDS that lack one of its fatty acyl chains due to its hydrolytic removal. Lysophosphatidic Acids,Lysophospholipid,Acids, Lysophosphatidic
D010710 Phosphates Inorganic salts of phosphoric acid. Inorganic Phosphate,Phosphates, Inorganic,Inorganic Phosphates,Orthophosphate,Phosphate,Phosphate, Inorganic
D010716 Phosphatidylinositols Derivatives of phosphatidic acids in which the phosphoric acid is bound in ester linkage to the hexahydroxy alcohol, myo-inositol. Complete hydrolysis yields 1 mole of glycerol, phosphoric acid, myo-inositol, and 2 moles of fatty acids. Inositide Phospholipid,Inositol Phosphoglyceride,Inositol Phosphoglycerides,Inositol Phospholipid,Phosphoinositide,Phosphoinositides,PtdIns,Inositide Phospholipids,Inositol Phospholipids,Phosphatidyl Inositol,Phosphatidylinositol,Inositol, Phosphatidyl,Phosphoglyceride, Inositol,Phosphoglycerides, Inositol,Phospholipid, Inositide,Phospholipid, Inositol,Phospholipids, Inositide,Phospholipids, Inositol
D010761 Phosphorus Radioisotopes Unstable isotopes of phosphorus that decay or disintegrate emitting radiation. P atoms with atomic weights 28-34 except 31 are radioactive phosphorus isotopes. Radioisotopes, Phosphorus
D011796 Quinacrine An acridine derivative formerly widely used as an antimalarial but superseded by chloroquine in recent years. It has also been used as an anthelmintic and in the treatment of giardiasis and malignant effusions. It is used in cell biological experiments as an inhibitor of phospholipase A2. Mepacrine,Acrichine,Atabrine,Atebrin,Quinacrine Dihydrochloride,Quinacrine Dihydrochloride, Dihydrate,Quinacrine Dihyrochloride, (R)-Isomer,Quinacrine Dihyrochloride, (S)-Isomer,Quinacrine Dimesylate,Quinacrine Hydrochloride,Quinacrine Monoacetate,Quinacrine Monohydrochloride,Quinacrine Monomesylate,Quinacrine, (+-)-Isomer,Quinacrine, (R)-Isomer,Quinacrine, (S)-Isomer,Dihydrochloride, Quinacrine,Dimesylate, Quinacrine,Hydrochloride, Quinacrine,Monoacetate, Quinacrine,Monohydrochloride, Quinacrine,Monomesylate, Quinacrine
D001792 Blood Platelets Non-nucleated disk-shaped cells formed in the megakaryocyte and found in the blood of all mammals. They are mainly involved in blood coagulation. Platelets,Thrombocytes,Blood Platelet,Platelet,Platelet, Blood,Platelets, Blood,Thrombocyte
D006736 Horses Large, hoofed mammals of the family EQUIDAE. Horses are active day and night with most of the day spent seeking and consuming food. Feeding peaks occur in the early morning and late afternoon, and there are several daily periods of rest. Equus caballus,Equus przewalskii,Horse, Domestic,Domestic Horse,Domestic Horses,Horse,Horses, Domestic
D006801 Humans Members of the species Homo sapiens. Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man

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