Adenosine Receptors of Cerebral Microvessels and Choroid Plexus

• Published in: Journal of cerebral blood flow and metabolism 1986-08, Vol.6 (4), p.463-470
• Main Authors: Kalaria, Rajesh N., Harik, Sami I.
• Format: Article
• Language: English
• Subjects: adenosine; Adenosine - analogs & derivatives; Adenosine - metabolism; Adenosine-5'-(N-ethylcarboxamide); Animals; Binding, Competitive; Biological and medical sciences; Brain - blood supply; Cerebral circulation. Blood-brain barrier. Choroid plexus. Cerebrospinal fluid. Circumventricular organ. Meninges; Cerebral Cortex - metabolism; cerebrum; choroid plexus; Choroid Plexus - metabolism; Female; Fundamental and applied biological sciences. Psychology; Male; Microcirculation - metabolism; microvasculature; Phenylisopropyladenosine - metabolism; pigs; Radioligand Assay; Rats; Rats, Inbred Strains; Receptors, Cell Surface - drug effects; Receptors, Cell Surface - metabolism; Receptors, Purinergic; Swine; Vertebrates: nervous system and sense organs
• ISSN: 0271-678X; 1559-7016
• DOI: 10.1038/jcbfm.1986.80

We studied, by ligand binding methods, the two adenosine receptors, A, and A2, in rat and pig cerebral microvessels and pig choroid plexus. Ligand binding to cerebral microvessels was compared with that to membranes of the cerebral cortex. [3H]Cyclohexyladenosine and [3H]l-phenylisopropyladenosine were the ligands used for A1-receptors, and [3H]5'-N-ethylcarboxamide adenosine ([3H]NECA) was used to assess A2-receptors. We report that cerebral microvessels and choroid plexus exhibit specific [3H]NECA binding, but have no appreciable A1-receptor ligand binding sites. Specific binding of [3H]NECA to cerebral microvessels, choroid plexus, and cerebral cortex was saturable and suggested the existence of two classes of A2-receptor sites: high-affinity (Kd ∼ 250 nM) and low-affinity (Kd ∼ 1–2 μM) sites. The Kd and Bmax of NECA binding to cerebral microvessels and cerebral cortex were similar within each species. Our results, indicating the existence of A2-receptors in cerebral microvessels, are consistent with results of increased adenylate cyclase activity by adenosine and some of its analogues in these microvessels.