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Defective platelet aggregation in polycythaemia vera is not caused by impaired calcium signaling, phospholipase D activation or decreased amounts of focal adhesion proteins
Author(s) -
Le Blanc Katarina,
Berg Anders,
Palmblad Jan,
Samuelsson Jan
Publication year - 2000
Publication title -
european journal of haematology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.904
H-Index - 84
eISSN - 1600-0609
pISSN - 0902-4441
DOI - 10.1034/j.1600-0609.2000.065005322.x
Subject(s) - platelet , calcium in biology , phospholipase c , intracellular , syk , tyrosine phosphorylation , rhoa , thrombin , stimulation , tyrosine , calcium , endocrinology , chemistry , phospholipase , medicine , platelet activation , tyrosine kinase , biochemistry , biology , signal transduction , enzyme
We have previously demonstrated that platelets in polycythaemia vera (PV) exhibit decreased aggregation after stimulation with platelet activating factor (PAF) and reduced expression of GPIIIa on both resting and stimulated platelets. In the present study, we investigated if these results were related to changes in the mobilization of intracellular calcium, activation of phospholipase D (PLD) or amounts of GPIIIa and the intracellular tyrosine kinases Fak, Syk, Grb2, Shc and rhoA. Intracellular calcium levels were not different in resting platelets from 14 PV patients and 15 healthy controls (median 43 nmol/L, range 10–114, vs. 36 nmol/L, range 10–119). After stimulation with PAF (1 µmol/L) an equal increase was seen (125 nmol/L for PV platelets, range 67–257, vs. 113 nmol/L for controls, range 60–250). Also formation of phosphatidyl ethanol (PEt) was similar after exposure to 0.5 U/ml thrombin (0.28% PEt of total phospholipid, range 0.16–1.10, vs. 0.24 for controls, range 0.11–2.3) and 1 µmol/L PMA (0.25, range 0.16–0.32, vs. 0.14, range 0.09–0.6). In contrast to the reduced amount of GPIIIa on the surface of PV platelets, immunoblotting on whole cell lysates showed no reduction in PV patients compared to controls, indicating the possibility of an impaired incorporation of GPIIIa to the cell membrane. Levels of Fak, Syk, Shc, Grb2 and rhoA appeared equal in patients and controls. Similar intracellular proteins were tyrosine phosphorylated after stimulation with thrombin, PAF and PMA. In summary, defective platelet aggregation after stimulation with PAF is caused by neither defective mobilization of intracellular calcium nor, in contrast to the situation in PV granulocytes, an impaired activation of PLD. Moreover, no apparent differences in the intracellular amounts of Fak, Syk Shc, Grb2 and rhoA could be detected between PV and control platelets.