Leukocyte count and leukocyte ecto-nucleotidase are major determinants of the effects of adenosine triphosphate and adenosine diphosphate on platelet aggregation in human blood.
ADP induces platelet aggregation in human whole blood and platelet-rich plasma (PRP). ATP induces aggregation in whole blood only; this involves leukocytes and is mediated by ADP. Here we studied ATP- and ADP-induced aggregation in patients with raised leukocyte counts (mean 46.2x10(3) leukocytes/microl). Platelet aggregation was measured by platelet counting. ATP, ADP and metabolites were measured by HPLC. Aggregation to ADP (1-10 microM) and ATP (10-100 microM) was markedly reduced, but to ATP (1000 microM) was enhanced (all p<0.001). Aggregation to ADP in PRP was normal. Increasing the leukocyte count in normal blood reproduced the findings in the patients. Adding leukocytes (either MNLs or PMNLs) to normal PRP enabled a response to ATP and caused marked inhibition of ADP-induced aggregation. Breakdown of ATP or ADP to AMP and adenosine in leukocyte-rich plasma was rapid (t1/2=4 min) and far higher than in cell-free plasma or PRP. With ATP there was also formation of ADP, maximal at 4 min. The presence of the ectonucleotidase NTPDase1 (CD39) was demonstrated on MNLs (all of the monocytes and a proportion of the lymphocytes) and all PMNLs by flow cytometry. We conclude that leukocytes provide a means of dephosphorylating ATP which enables ATP-induced aggregation via conversion to ADP, but also convert ADP to AMP and adenosine. Platelet aggregation extent is a balance between these activities, and high white cell counts influence this balance.
Glenn
Jacqueline R
JR
Centre for Integrated Systems Biology and Medecine, Institute of Clinical Research, University of Nottingham, Nottingham, UK.
White
Ann E
AE
Johnson
Andrew
A
Fox
Susan C
SC
Behan
Miles W H
MW
Dolan
Gerry
G
Heptinstall
Stanley
S
D000244:Adenosine Diphosphate / Q000378:metabolism / Q000494:pharmacology*; D000249:Adenosine Monophosphate; D000251:Adenosine Triphosphatases / Q000032:analysis / Q000502:physiology*; D000255:Adenosine Triphosphate / Q000378:metabolism / Q000494:pharmacology*; D015703:Antigens, CD / Q000032:analysis; D001081:Apyrase / Q000032:analysis; D002450:Cell Communication; D006801:Humans; D007958:Leukocyte Count; D007962:Leukocytes / Q000201:enzymology* / Q000502:physiology*; D010766:Phosphorylation; D010974:Platelet Aggregation / Q000187:drug effects*; D010979:Platelet Function Tests
D015703:Antigens, CD; D000249:Adenosine Monophosphate; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; C027201:ectoATPase; D001081:Apyrase; C067869:CD39 antigen