title: Protein, not adenosine or adenine nucleotides, mediates platelet decrease in endothelial permeability.
abstract: Platelets and platelet-conditioned medium (PCM) decrease endothelial protein permeability in vitro. Adenosine and a > 100-kDa protein have previously been implicated as the soluble factors released from platelets that decrease endothelial permeability. The objective of this study was to further investigate the role of adenosine in this platelet response. Measurements of adenosine and its precursor adenine nucleotides by high-performance liquid chromatography were correlated with the assessment of permeability by 125I-labeled albumin clearance and electrical resistance across endothelial cell monolayers derived from the bovine pulmonary artery. PCM contained micromolar concentrations of AMP, ADP, and ATP, but adenosine was below detectable levels (< or = 0.1 microM). Adenosine deaminase, an enzyme that converts adenosine to inactive inosine, or an adenosine-receptor antagonist did not block the platelet- or PCM-mediated decrease in endothelial permeability. A < 3-kDa fraction of PCM that contained micromolar concentrations of AMP and ADP did not affect endothelial permeability, whereas a > 3-kDa fraction that contained much reduced levels of AMP and ADP significantly decreased permeability. This activity of PCM was sensitive to insoluble trypsin. This study rules out adenosine and adenine nucleotides as primary factors in the platelet-induced decrease in endothelial permeability and suggests that the active factor is a protein.
authors.affiliation: Department of Physiology and Cell Biology, Albany Medical College, Union University, New York 12208, USA.
authors.forename: S
authors.initials: S
authors.lastname: Patil
authors.forename: J E
authors.initials: JE
authors.lastname: Kaplan
authors.forename: F L
authors.initials: FL
authors.lastname: Minnear
mesh_terms: D000227:Adenine Nucleotides / Q000494:pharmacology*; D000241:Adenosine / Q000494:pharmacology*; D000243:Adenosine Deaminase / Q000494:pharmacology; D058892:Adenosine Deaminase Inhibitors; D000244:Adenosine Diphosphate / Q000494:pharmacology; D000249:Adenosine Monophosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001792:Blood Platelets / Q000502:physiology*; D001798:Blood Proteins / Q000494:pharmacology / Q000502:physiology*; D002417:Cattle; D002463:Cell Membrane Permeability / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D017077:Culture Media, Conditioned; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D011651:Pulmonary Artery; D014970:Xanthines / Q000494:pharmacology
chemical_list: D000227:Adenine Nucleotides; D058892:Adenosine Deaminase Inhibitors; D001798:Blood Proteins; D017077:Culture Media, Conditioned; D014970:Xanthines; C056346:BW A1433; D000249:Adenosine Monophosphate; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D000243:Adenosine Deaminase; D000241:Adenosine