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Differential Binding Properties of Adenosine Receptor Agonists and Antagonists in Brain
Author(s) -
Marangos Paul J.,
Patel Jitendra,
Martino Andrea M.,
Dilli Mark,
Boulenger Jean Philippe
Publication year - 1983
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1983.tb04752.x
Subject(s) - chemistry , copper , adenosine , binding site , zinc , ligand (biochemistry) , stereochemistry , cadmium , adenosine receptor , guanine , nucleotide , receptor , biochemistry , agonist , gene , organic chemistry
The binding properties of N 6 ‐cydohexyl [ 3 H]adenosine ([ 3 H]CHA) and 1, 3‐diethyl‐8‐[ 3 H]phenyl‐xanthine ([ 3 H]DPX) in rat forebrain membrane are compared. The kinetic parameters of binding for each ligand are quite distinct, with [ 3 H]CHA displaying two populations of binding sites ( K D = 0.4 ± 0.05 nM and 4.2 ± 0.3 nM; B max = 159 ± 17 and 326 ± 21 fmol/mg protein), whereas [ 3 H]DPX yielded monophasic Scatchard plots ( K D = 13.9 ±1.1 n M;B max = 634 ± 27 fmol/mg protein). The metals copper, zinc, and cadmium are potent inhibitors of [ 3 H]CHA binding, with respective IC 50 concentrations of 36 [μM , 250 )μM , and 70 μM . Copper is a much less potent inhibitor of [ 3 H]DPX binding (IC 50 = 350 μM ). The inhibitory effect of copper on both [ 3 H]CHA and [ 3 H]DPX binding is apparently irreversible, as membranes pretreated with copper cannot be washed free of its inhibitory effect. The inhibitory effect of both copper and zinc on [ 3 H]CHA binding was reversed by the guanine nucleotide Gpp(NH)p. [ 3 H]DPX binding is only partially inhibited by zinc and cadmium (60% of specific binding remains unaffected), suggesting that this adenosine receptor ligand binds to two separate sites. Guanine nucleotides had no effect on the inhibition of [ 3 H]DPX binding by either copper or zinc. Differential thermal and proteolytic denaturation profiles are also observed for [ 3 H]CHA and [ 3 H]DPX binding, with the former ligand binding site being more labile in both cases. Stereospecificity is observed in the inhibition of both [ 3 H]CHA and [ 3 H]DPX binding, with l‐ N ‐phenylisopropyladenosine (PIA) being 50‐fold more potent than d‐PIA in both cases. Evidence is therefore provided that adenosine receptor agonists and antagonists have markedly different binding properties to brain adenosine receptors.