Adenosine diphosphate stimulation of cultured hematopoietic cell lines
SA Kalambakas, FM Robertson, SM O'Connell, S Sinha, K Vishnupad and GI Karp
Department of Medicine, UMDNJ-Robert Wood Johnson Medical School, New
Brunswick 08903-0019.
Adenosine diphosphate (ADP) plays a critical role in platelet activation
both by exogenous stimulation and the release of endogenous intracellular
stores. As the platelet ADP receptor is not well defined, we have chosen to
identify and characterize several cell lines that possess functional
receptors for this nucleotide. Rat promegakaryoblasts (RPM), human
erythroleukemia cells (HEL), U937, and K562 leukemia cells responded to
ADP, as measured by a rapid increase in intracellular calcium. In the case
of RPM cells, ADP was the only naturally occurring platelet agonist capable
of eliciting this response. Binding studies with [3H]ADP and fixed cells
showed 3.99 +/- 1.77 x 10(5) binding sites/cell for RPM cells (apparent
dissociation constant [kd] = 7.75 +/- 2.3 x 10(-8) mol/L), 8.19 +/- 3.25 x
10(5) sites/cell for HEL cells (kd = 2.15 +/- 0.84 x 10(-7) mol/L, 1.15 +/-
0.23 x 10(6) sites/cell for U937 cells (kd = 2.20 +/- 0.53 x 10(-7) mol/L)
and 5.39 +/- 2.80 x 10(5) sites/cell for K562 cells (kd = 1.37 +/- 0.39 x
10(-7) mol/L), Inhibition studies with unlabeled nucleotides and analogues
showed that binding was approximately 85% specific and the inhibitory
pattern was similar to that seen with mature platelets. The purine base
adenosine resulted in little or no inhibition. These studies indicate that
both human and rat hematopoietic cell lines possess intact ADP receptors
and may be useful tools in future studies of the structure and function of
this important platelet-activation system.
Volume 81,
Issue 10,
pp. 2652-2657,
05/15/1993
Copyright © 1993 by The American Society of Hematology
