phosphorus-radioisotopes and Blood-Platelet-Disorders

Topics: Blood Platelet Disorders; Blood Platelets; Carbon Radioisotopes; Cell Survival; Chromium Radioisotopes; Humans; Isoflurophate; Isotope Labeling; Phosphorus Radioisotopes; Platelet Adhesiveness; Platelet Aggregation; Radioisotopes; Selenomethionine

We have examined platelet functional responses and characterized a novel signaling defect in the platelets of a patient suffering from a chronic bleeding disorder. Platelet aggregation responses stimulated by weak agonists such as adenosine diphosphate (ADP) and adrenaline were severely impaired. In comparison, both aggregation and dense granule secretion were normal following activation with high doses of collagen, thrombin, or phorbol-12 myristate-13 acetate (PMA). ADP, thrombin, or thromboxane A2 (TxA2) signaling through their respective Gq-coupled receptors was normal as assessed by measuring either mobilization of intracellular calcium, diacylglycerol (DAG) generation, or pleckstrin phosphorylation. In comparison, Gi-mediated signaling induced by either thrombin, ADP, or adrenaline, examined by suppression of forskolin-stimulated rise in cyclic AMP (cAMP) was impaired, indicating dysfunctional Galphai signaling. Immunoblot analysis of platelet membranes with specific antiserum against different Galpha subunits indicated normal levels of Galphai2,Galphai3,Galphaz, and Galphaq in patient platelets. However, the Galphai1level was reduced to 25% of that found in normal platelets. Analysis of platelet cDNA and gDNA revealed no abnormality in either the Galphai1 or Galphai2 gene sequences. Our studies implicate the minor expressed Galphai subtype Galphai1 as having an important role in regulating signaling pathways associated with the activation of alphaIIbbeta3 and subsequent platelet aggregation by weak agonists.

Topics: Adenosine Diphosphate; Adult; Arachidonic Acid; Blood Platelet Disorders; Blood Platelets; Calcium; Carbon Radioisotopes; Cell Membrane; Colforsin; Collagen; Cyclic AMP; Diglycerides; DNA, Complementary; Epinephrine; GTP-Binding Protein alpha Subunits, Gi-Go; Humans; Male; Monocytes; Phosphorus Radioisotopes; Platelet Aggregation; Sequence Analysis, DNA; Serotonin; Signal Transduction; Thrombin; Thromboxane B2; Tritium

By the term "Primary Secretion Defect" (PSD), we mean a common heterogeneous group of congenital defects of platelet secretion, characterized by a normal primary wave of platelet aggregation induced by ADP and other agonists, a normal concentration of platelet granule contents, and normal production of thromboxane A2. The biochemical abnormalities responsible for PSD are not well known. Since a secretion defect similar to PSD is found in platelets that are severely deficient of binding sites for the ADP analogue 2MeS-ADP and do not aggregate in response to ADP, we tested the hypothesis that PSD platelets have moderately decreased 2MeS-ADP binding sites, which may be sufficient for normal ADP-induced aggregation but not for potentiating platelet secretion. The specific binding of [33P]2MeS-ADP to platelets from 3 PSD patients (347, 443 and 490 sites/platelet; KD 2.8-3.9 nM) was lower than to platelets from 24 normal subjects (647 [530-1102]; KD = 3.8 [2.3-7.3]) (median [range]). Normal values were found in a fourth PSD patient (710; KD 3.7). The degree of inhibition of PGE1-induced cAMP increase by 0.1 microM ADP was lower in patients than in controls. The secretion induced by the endoperoxide analogue U46619 from normal, acetylsalicylic acid-treated platelets under conditions that prevented the formation of large aggregates was potentiated by 1 mumol/l ADP and inhibited by apyrase. These findings indicate that a partial deficiency of the platelet ADP receptor(s) might be responsible for the defect of platelet secretion in some PSD patients and that ADP potentiates platelet secretion independently of the formation of large aggregates and thromboxane A2 production.

Topics: Adenosine Diphosphate; Adenosine Triphosphate; Adult; Binding Sites; Blood Platelet Disorders; Blood Platelets; Cytoplasmic Granules; Female; Fibrinogen; Humans; In Vitro Techniques; Kinetics; Male; Middle Aged; Phosphorus Radioisotopes; Platelet Aggregation; Reference Values; Serotonin; Thionucleotides; Thromboxane A2

Topics: Adipose Tissue; Adult; Agammaglobulinemia; Arteritis; Arthritis, Rheumatoid; Autopsy; Blood Platelet Disorders; Bronchopneumonia; Chlorambucil; Chronic Disease; Colon; Dexamethasone; Female; Hematopoiesis; Humans; Lung; Lung Diseases, Obstructive; Lymph Nodes; Lymphoma, Non-Hodgkin; Necrosis; Panniculitis, Nodular Nonsuppurative; Phosphorus Radioisotopes