Inhibition of agonist-induced platelet aggregation, Ca2+ mobilization and granule secretion by guanosine 5'-[beta-thio]diphosphate and GDP in intact platelets. Evidence for an inhibitory mechanism unrelated to the inhibition of G-protein-GTP interaction.
The effect of guanosine 5'-[beta-thio]diphosphate (GDP[beta S]), reported to be an antagonist of GTP at the G-protein-binding site, on human platelet activation was examined. GDP[beta S] (0.3-3 mM) had significant inhibitory effects on platelet aggregation and 5-hydroxytryptamine (5HT) secretion induced by thrombin, collagen, the thromboxane mimetic U46619 and 1,2-dioctanoylglycerol (diC8) in intact platelets, as well as in saponin-permeabilized platelets. Similar inhibitory effects in intact platelets were also observed with ATP (over similar concentration ranges) and GDP and GTP (at 2- and 10-fold higher concentrations respectively). All four nucleotides also inhibited ADP-induced platelet aggregation in indomethacin-treated platelets under conditions where no 5HT secretion occurred. Inhibition of thrombin-induced aggregation and secretion by GDP[beta S] and ATP in intact platelets was accompanied by a reduction in the thrombin-induced rise in intracellular Ca2+ levels and 45 kDa-protein phosphorylation. The results suggest that at least some of the effects of GDP[beta S] may be unrelated to inhibition of G-protein-GTP interaction, but, instead, may be mediated via an extracellular site, common to all the nucleotides tested and perhaps via inhibition of the effects of endogenous/released ADP. The usefulness of GDP[beta S] as a tool in studying G-protein-GTP interactions in platelets is thus questionable.
Krishnamurthi
S
S
Thrombosis Research Unit, Rayne Institute, King's College School of Medicine and Dentistry, London, U.K.
Patel
Y
Y
Kakkar
V V
VV
D000255:Adenosine Triphosphate / Q000494:pharmacology; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D001798:Blood Proteins / Q000378:metabolism; D002118:Calcium / Q000097:blood*; D003094:Collagen / Q000494:pharmacology; D003594:Cytoplasmic Granules / Q000378:metabolism; D006150:Guanine Nucleotides / Q000494:pharmacology*; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives* / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D009711:Nucleotides / Q000494:pharmacology; D010974:Platelet Aggregation / Q000187:drug effects; D012701:Serotonin / Q000097:blood; D013873:Thionucleotides / Q000494:pharmacology*; D013917:Thrombin / Q000494:pharmacology
D001798:Blood Proteins; D006150:Guanine Nucleotides; D009711:Nucleotides; D013873:Thionucleotides; D006153:Guanosine Diphosphate; D012701:Serotonin; C023427:guanosine 5'-O-(2-thiodiphosphate); D000255:Adenosine Triphosphate; D003094:Collagen; D013917:Thrombin; D002118:Calcium