Human erythroleukemia cells express functional thromboxane A2/prostaglandin H2 receptors

The human erythroleukemia (HEL) cell line is a cultured hematopoietic cell line reported to express platelet membrane glycoproteins and alpha-2 adrenergic receptors. The present studies were designed to determine if functional thromboxane A2 (TXA2)/prostaglandin H2 (PGH2) receptors exist in HEL cells. Radioligand binding assays were performed using [125I]PTA-OH, a TXA2/PGH2 receptor antagonist. Scatchard analysis revealed one class of binding sites for 1-PTA-OH with a Kd = 122 +/- 18 nM and maximum binding = 1.7 +/- 0.3 x 10(5) sites/cell. Competition for [125I]PTA-OH binding with the TXA2/PGH2 receptor agonists SQ26655 and U46619 revealed one class of binding sites for SQ26655 with a Kd = 17 nM and two classes of binding sites for for U46619 with a Kd = 45 nM for the high-affinity site and a Kd = 450 nM for the low-affinity site. Competition for [125I]PTA-OH by the steroisomeric TXA2/PGH2 receptor antagonists L657925 and L657926 revealed two classes of binding sites for the more potent L657925 with a Kd = 8 nM for the high-affinity site and a Kd = 400 nM for the low-affinity site whereas L657926 bound to one class of sites with a Kd = 380 nM. Stimulation of the TXA2/PGH2 receptor by SQ26655 and U46619 resulted in concentration-dependent increases in [Ca++], as measured by FURA-2 fluorescence, with EC50 values of 28 +/- 2 and 149 +/- 32 nM, respectively. I-PTA-OH, L657925 and L657926 antagonized this response to U46619 with IC50 values similar in rank potency to that seen in the binding studies.(ABSTRACT TRUNCATED AT 250 WORDS)