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Solubilized Rat Brain Adenosine Receptors Have Two High‐Affinity Binding Sites for l, 3‐Dipropyl‐8‐Cyclopentylxanthine
Author(s) -
Oliveira Júlia C.,
Sebastião A. M.,
Ribeiro J. A.
Publication year - 1991
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.1471-4159.1991.tb08275.x
Subject(s) - receptor , binding site , adenosine receptor , dissociation constant , agonist , adenosine , membrane , chemistry , adenosine a1 receptor , gtp' , stereochemistry , medicine , biophysics , biology , biochemistry , endocrinology , enzyme
The specific binding of L‐ N 6 ‐[ 3 H]phenylisopropyladenosine (L‐[ 3 H]PIA) to solubilized receptors from rat brain membranes was studied. The interaction of these receptors with relatively low concentrations of L‐[ 3 H]PIA (0.5–12.0 nA/) in the presence of Mg 2+ showed the existence of two binding sites for this agonist, with respective dissociation constant ( K D ) values of 0.24 and 3.56 nM and respective receptor number ( B max ) values of 0.28 ± 0.03 and 0.66 ± 0.05 pmol/mg of protein. In the presence of GTP, the binding of L‐[ 3 H]PIA also showed two sites with K D values of 24.7 and 811.5 n M and B max values of 0.27 ± 0.09 and 0.93 ± 0.28 pmol/mg of protein for the first and the second binding site, respectively. Inhibition of specific L‐[ 3 H]PIA binding by 1, 3‐dipropyl‐8‐cydopentylxanthine (DPCPX) (0.1–300 n M ) performed with the same preparations revealed two DPCPX binding sites with K i values of 0.29 and 13.5 n M , respectively. [ 3 H]DPCPX saturation binding experiments also showed two binding sites with respective K D values of 0.81 and 10.7 n M and respective B max values of 0.19 ± 0.02 and 0.74 ± 0.06 pmol/mg of protein. The results suggest that solubilized membranes from rat brain possess two adenosine receptor subtypes: one of high affinity with characteristics of the A 1 subtype and another with lower affinity with characteristics of the A 3 subtype of adenosine receptor.