The objective of this proposal is to delineate the mechanisms by which stimuli activate platelets and to determine how agents that increase cAMP (e.g. prostacyclin) inhibit platelet responses to stimulation. Various physiological stimulants (thrombin, collagen, ADP, platelet activating factor) cause platelets to change shape, secrete and aggregate. These responses enable the platelet to fulfill its important role in hemostasis, and may also contribute to thrombosis and atherosclerosis. Ca2+ is vitally involved in enabling or facilitating the biochemical reactions necessary for platelet responses, whereas cAMP opposes all platelet responses. cAMP blocks mobilization of Ca2+ (measured with Quin2) by stimuli, and also inhibits the hydrolysis of phosphatidylinositol 4,5-bisphosphate that generates two important substances; 1,2-diacylglycerol (DG) and inositol 1,4,5-trisphosphate (IP3). DG acts cooperatively with Ca2+ mobilized by ionophores to facilitate protein phosphorylation and secretion. In this project the role of DG in the responses of intact platelets to thrombin, and how its production and actions are affected by physiological stimulants of adenylate cyclase (e.g. prostacylin) will be studied. IP3 is thought to be mediate hormone-induced mobilization of Ca2+ in several cells. In isolated platelet membrane vesicles that have an ATP-dependent pump to accumulate Ca2+ we find that IP3 released Ca2+ providing the first evidence that IP3 may be the second messenger for intracellular Ca2+ mobilization in platelets. This effect of IP3 will be studied in detail to determine if IP3 mobilizes Ca2+ in permeabilized intact platelets, to identify the membrane site(s) and mechanism of action, and whether cAMP affects the action of IP3. The temporal and quantitative relationships between formation of IP3 and Ca2+ mobilization will be studied in control and prostacyclin-treated intact platelets to determine if IP3 can be the second messenger linking stimulation of surface membrane receptors to internal cellular responses. In thrombin-treated platelets the inhibitory action of prostacyclin is antagonized by epinephrine and ADP, thereby affecting Ca2+ mobilization and lipid metabolism. Epinephrine and ADP act through a GTP-binding protein (Ni) that inhibits adenylate cyclase, but which may have other important effects as well. This project shall study the mechanism(s) of action of epinephrine and ADP on Ca2+ mobilization, DG and IP3 formation, and DG and IP3 actions, because these agents may importantly influence the antithrombotic action of prostacyclin.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL018937-11
Application #
3335700
Study Section
Hematology Subcommittee 2 (HEM)
Project Start
1979-04-01
Project End
1990-03-31
Budget Start
1987-04-01
Budget End
1988-03-31
Support Year
11
Fiscal Year
1987
Total Cost
Indirect Cost
Name
University of Connecticut
Department
Type
School of Medicine & Dentistry
DUNS #
City
Farmington
State
CT
Country
United States
Zip Code
06030
Laplante, J M; O'Rourke, F; Lu, X et al. (2000) Cloning of human Ca2+ homoeostasis endoplasmic reticulum protein (CHERP): regulated expression of antisense cDNA depletes CHERP, inhibits intracellular Ca2+ mobilization and decreases cell proliferation. Biochem J 348 Pt 1:189-99
O'Rourke, F; Matthews, E; Feinstein, M B (1996) Isolation of InsP4 and InsP6 binding proteins from human platelets: InsP4 promotes Ca2+ efflux from inside-out plasma membrane vesicles containing 104 kDa GAP1IP4BP protein. Biochem J 315 ( Pt 3):1027-34
O'Rourke, F; Matthews, E; Feinstein, M B (1995) Purification and characterization of the human type 1 Ins(1,4,5)P3 receptor from platelets and comparison with receptor subtypes in other normal and transformed blood cells. Biochem J 312 ( Pt 2):499-503
O'Rourke, F; Soons, K; Flaumenhauft, R et al. (1994) Ca2+ release by inositol 1,4,5-trisphosphate is blocked by the K(+)-channel blockers apamin and tetrapentylammonium ion, and a monoclonal antibody to a 63 kDa membrane protein: reversal of blockade by K+ ionophores nigericin and valinomycin and purificati Biochem J 300 ( Pt 3):673-83
Banga, H S; Halenda, S P; Feinstein, M B (1991) Potentiation of arachidonic acid release by phorbol myristate acetate in platelets is not due to inhibition of arachidonic acid uptake or incorporation into phospholipids. Biochim Biophys Acta 1091:115-9
O'Rourke, F; Feinstein, M B (1990) The inositol 1,4,5-trisphosphate receptor binding sites of platelet membranes. pH-dependency, inhibition by polymeric sulphates, and the possible presence of arginine at the binding site. Biochem J 267:297-302
Pumiglia, K M; Huang, C K; Feinstein, M B (1990) Elevation of cAMP, but not cGMP, inhibits thrombin-stimulated tyrosine phosphorylation in human platelets. Biochem Biophys Res Commun 171:738-45
Halenda, S P; Banga, H S; Zavoico, G B et al. (1989) Synergistic release of arachidonic acid from platelets by activators of protein kinase C and Ca2+ ionophores. Evidence for the role of protein phosphorylation in the activation of phospholipase A2 and independence from the Na+/H+ exchanger. Biochemistry 28:7356-63
O'Rourke, F; Zavoico, G B; Feinstein, M B (1989) Release of Ca2+ by inositol 1,4,5-trisphosphate in platelet membrane vesicles is not dependent on cyclic AMP-dependent protein kinase. Biochem J 257:715-21
Feinstein, M B; Halenda, S P (1988) Arachidonic acid mobilization in platelets: the possible role of protein kinase C and G-proteins. Experientia 44:101-4

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