ISSN:
1471-4159
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Medicine
Notes:
Abstract: Membranes from adult chicken brain have high-affinity binding sites for N6-cyclohexyl[3H]adenosine (CHA) (KD= 4 nM, Bmax= 0.6 pmol/mg protein). This CHA binding could be attributed to adenosine receptors of the A1 type, since substituted adenosine analogs, e.g. N6-(l-2-phenylisopropyl)adeno sine (IC50= 60 nM), were very potent displacers. Binding sites for 1,3-diethyl- 8-[3H]phenylxanthine (DPX) in adult brain membranes have a moderate affinity (KD= 50 nM, Bmax= 1.5 pmol/mg). The association of DPX with these sites could be completely displaced by 8-phenyltheophylline (IC50= 300 nM) and other xanthines, but only 45% of specific DPX binding could be displaced by phenylisopropyladenosine. This suggests that about half of DPX sites are putative A1 receptors and the other half are of the A2 type. Primary cultures of pure glial and neuronal cells from chick embryo brain were also examined for adenosine receptors. Specific binding of CHA could not be detected in these preparations, but both glial and neuronal membranes have specific sites for DPX. At a [3H]DPX concentration of 20 nM, specific binding was 50% higher (per mg protein) in glial than in neuronal membranes. The maximum binding of DPX to glial membranes (Bmax= 1.6 pmol/mg) was comparable to values for adult brain, but the glial affinity (KD= 90 nM) was somewhat less. Phenylisopropyladenosine was able to displace less than 20% of the total glial sites for DPX. This finding was in accord with the lack of CHA sites and demonstrates that A1 receptors make little contribution to DPX binding in glial membranes. In decreasing order of potency, 8-phenyltheophylline, CHA, theophylline, caffeine, and 3-isobutyl-I-methylxanthine completely displace DPX association with glia. DPX binding to glial membranes thus appears due to a single class of receptors, which may prove to be of the A2 type.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1471-4159.1982.tb07941.x
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