Abstract
The present study was designed to evaluate the effects of novel and
recognised compounds at human recombinant A(2B) adenosine receptors
expressed in Chinese hamster ovary (hA(2B)CHO), in human embryonic
kidney 293 (hA(2B)HEK-293) and at endogenous A(2B) receptors in human
mast cells (HMC-1). Saturation binding experiments performed using
the new high affinity A(2B) adenosine radioligand (3)H-N-benzo1,3dioxol-5-yl-2-5-(2,6-dioxo-1,3-dipropyl-2,3,6,7-tetra
hydro-1H-purin-8-yl)-1-methyl-1H-pyrazol-3-yloxy-acetamide ((3)H-MRE
2029F20) revealed a single class of binding sites in hA(2B)CHO, hA(2B)HEK-293
and HMC-1 cells with K(D) (nM) of 1.65+/-0.18, 2.83+/-0.34, 2.62+/-0.27
and B(max) (fmol/mg protein) of 36+/-4, 475+/-50 and 128+/-15, respectively.
The pharmacological profile of new compounds, determined in inhibition
binding experiments in hA(2B)HEK-293 cells using (3)H-MRE 2029F20,
showed a rank order of potency typical of the A(2B) receptors with
K(i) values in the range 3.2-28nM. In functional assays, recognised
agonists and antagonists were studied by evaluating their capability
to modulate the cAMP production in hA(2B)CHO and in HMC-1 cells.
Novel compounds were able to decrease NECA-stimulated cAMP production
in hA(2B)CHO and in HMC-1 cells showing a high potency. New compounds
were also able to inhibit cAMP levels in the absence of NECA and
in the presence of forskolin stimulation in hA(2B)CHO and in HMC-1
cells. In HEK-293 cells MRE 2029F20 reduced cAMP basal levels with
an IC(50) value of 2.9+/-0.3nM. These results suggest that novel
compounds are antagonists with an inverse agonist activity in recombinant
and native human A(2B) receptors.
Users
Please
log in to take part in the discussion (add own reviews or comments).