Glycoprotein IIb-IIIa complex and Ca2+ influx into stimulated platelets.
Changes in intracellular Ca2+ concentrations [( Ca2+]i) in platelets stimulated with aggregating agents were measured with the fluorescent indicator dye quin 2. Ca2+ influx, but not intracellular mobilization, in response to adenosine diphosphate (ADP), platelet aggregating factor (PAF-acether), and sodium arachidonate was significantly inhibited by monoclonal antibodies against the glycoprotein (GP) IIb-IIIa complex; inhibition of thrombin-stimulated influx was inhibited to a lesser extent and reached statistical significance only at thrombin concentrations of 0.1 U/mL and below. Anti-GP Ib and HLA-ABC monoclonal antibodies had no effect on Ca2+ influx in response to any agonist. Thrombasthenic platelets gave normal [Ca2+]i responses to ADP and thrombin, which were not inhibited by an anti-GP IIb-IIIa antibody. It is suggested that Ca2+ influx in response to weak agonists occurs predominantly via a channel closely adjacent to the GP IIb-IIIa complex, but that higher concentrations of thrombin and A23187 also stimulate influx via another pathway.
Powling
M J
MJ
Hardisty
R M
RM
D000244:Adenosine Diphosphate / Q000494:pharmacology; D001693:Biological Transport, Active; D001791:Blood Platelet Disorders / Q000097:blood; D001792:Blood Platelets / Q000378:metabolism* / Q000502:physiology; D002118:Calcium / Q000378:metabolism*; D006023:Glycoproteins / Q000276:immunology* / Q000502:physiology; D006801:Humans; D008565:Membrane Proteins / Q000276:immunology* / Q000502:physiology; D010974:Platelet Aggregation; D010980:Platelet Membrane Glycoproteins; D013917:Thrombin / Q000494:pharmacology
D006023:Glycoproteins; D008565:Membrane Proteins; D010980:Platelet Membrane Glycoproteins; D000244:Adenosine Diphosphate; D013917:Thrombin; D002118:Calcium