Abstract
Human platelets stimulated with alpha-thrombin or the thromboxane A2 analogue U46619 form the novel phosphatidylinositol (PtdIns) polyphosphate species PtdIns (3,4)P2 and PtdIns(3,4,5)P3 in a time- and dose-dependent manner. In [32P]o-phosphate-labeled platelets, PtdIns(3,4)P2 increases in 2 min to 613% of the basal level in response to 1 unit/ml alpha-thrombin and 295% in response to 5 microM U46619. A dramatic increase is also observed with myo-[3H]inositol-labeled platelets. [32P]PtdIns(3,4,5)P3 is increased with alpha-thrombin and U46619 stimulation by 261 and 183%, respectively. PtdIns(3)P quantities remain nearly equal to those under resting conditions. Neither the basal nor increased levels of PtdIns(3,4)P2 appear to be adequate to account for the rapid elevation of Ins(1,3,4)P3 that we have observed in alpha-thrombin-stimulated platelets. A23187 and/or phorbol 12,13-dibutyrate are not as potent as alpha-thrombin in stimulating changes in PtdIns(3,4)P2 or PtdIns(3,4,5)P3. GTP gamma S (10 microM), however, increases the level of PtdIns(3,4)P2 by 3736% and that of PtdIns(3,4,5)P3 by 456% in saponin-permeabilized platelets incubated with 0.5 mM [gamma-32P]ATP, implying a role for a GTP-binding protein in promoting phosphatidylinositide 3-kinase activity(ies). This is the first report of stimulated generation of 3-phosphorylated phosphoinositides in anucleate cells. A role for these novel phospholipid species in signal transduction, however, awaits elucidation.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.