ISSN:
1471-4159
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Medicine
Notes:
Abstract: The binding properties of N6-cydohexyl [3H]adenosine ([3H]CHA) and 1, 3-diethyl-8-[3H]phenyl-xanthine ([3H]DPX) in rat forebrain membrane are compared. The kinetic parameters of binding for each ligand are quite distinct, with [3H]CHA displaying two populations of binding sites (KD= 0.4 ± 0.05 nM and 4.2 ± 0.3 nM; Bmax= 159 ± 17 and 326 ± 21 fmol/mg protein), whereas [3H]DPX yielded monophasic Scatchard plots (KD= 13.9 ±1.1 nM;Bmax= 634 ± 27 fmol/mg protein). The metals copper, zinc, and cadmium are potent inhibitors of [3H]CHA binding, with respective IC50 concentrations of 36 [μM, 250 )μM, and 70 μM. Copper is a much less potent inhibitor of [3H]DPX binding (IC50= 350 μM). The inhibitory effect of copper on both [3H]CHA and [3H]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 [3H]CHA binding was reversed by the guanine nucleotide Gpp(NH)p. [3H]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 [3H]DPX binding by either copper or zinc. Differential thermal and proteolytic denaturation profiles are also observed for [3H]CHA and [3H]DPX binding, with the former ligand binding site being more labile in both cases. Stereospecificity is observed in the inhibition of both [3H]CHA and [3H]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.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1471-4159.1983.tb04752.x
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