Xd. Ji et al., A SELECTIVE AGONIST AFFINITY LABEL FOR A(3) ADENOSINE RECEPTORS, Biochemical and biophysical research communications, 203(1), 1994, pp. 570-576
A newly synthesized, chemically reactive adenosine derivative, othiocy
anatobenzyl)adenosine-5'-N-methyluronamide, was found to bind selectiv
ely to A(3) receptors. K-i values for this isothiocyanate derivative i
n competition binding at rat brain A(1), A(2a), and A(3) receptors wer
e 145, 272 and 10.0 nM, respectively. A preincubation with this deriva
tive resulted in irreversible inhibition of radioligand binding at rat
A(3) receptors in membranes of transfected CHO cells or RBL-2H3 mast
cells, but not at rat A(1) or A(2a) receptors. The loss of binding sit
es for 0.1 nM N-6-(4-aminobenzyl)adenosine-5'-N-methyluronamide, a hig
h affinity A(3) receptor radioligand, in transfected CHO cell membrane
s was concentration-dependent with an IC50 of 50 n M. No change was ob
served in the K-d value of the remaining A(3) receptor sites. The inhi
bition was also insensitive to theophylline (1 mM), consistent with th
e pharmacology of rat A(3) receptors. Structurally similar adenosine a
nalogues lacking the chemically reactive isothiocyanate group failed t
o irreversibly inhibit A(3)-binding. (C) 1994 Academic Press, Inc.