Characterization of nitrobenzylthioinosine binding to nucleoside transport sites selective for adenosine in rat brain

Journal Article · Fri Mar 01 04:00:00 EST 1985 · J. Neurosci.; (United States)

OSTI ID:5483823

Geiger, J D; LaBella, F S; Nagy, J I

Nucleoside transport sites in rat brain membrane preparations were labeled with (/sup 3/H)nitrobenzylthioinosine ((/sup 3/H) NBI), a potent inhibitor of nucleoside transport systems. The membranes contained a single class of very high affinity binding sites with K/sub D/ and B/sub max/ values of 0.06 nM and 147 fmol/mg of protein, respectively. The displacement of (/sup 3/H)NBI binding by various nucleosides, adenosine receptor agonists and antagonists, and known nucleoside transport inhibitors was examined. The K/sub i/ values (micromolar concentration) of (/sup 3/H)NBI displacement by the nucleosides tested were: adenosine, 3.0; inosine, 160; thymidine, 240; uridine, 390; guanosine, 460; and cytidine, 1000. These nucleosides displayed parallel displacement curves indicating their interaction with a common site labeled by (/sup 3/H)NBI. The nucleobases, hypoxanthine and adenine, exhibited K/sub i/ values of 220 and 3640 microM, respectively. Adenosine receptor agonists exhibited moderate affinities for the (/sup 3/H)NBI site, whereas the adenosine receptor antagonists, caffeine, theophylline, and enprofylline, were ineffective displacers. The K/sub i/ values for cyclohexyladenosine, (+)- and (-)-phenylisopropyladenosine, 2-chloroadenosine, and adenosine 5'-ethylcarboxamide were 0.8, 0.9, 2.6, 12, and 54 microM, respectively. These affinities and the rank order of potencies indicate that (/sup 3/H)NBI does not label any known class of adenosine receptors (i.e., A1, A2, and P). The K/sub i/ values of other nucleoside transport inhibitors were: nitrobenzylthioguanosine, 0.05 nM; dipyridamole, 16 nM; papaverine, 3 microM; and 2'-deoxyadenosine, 22 microM. These results indicate that (/sup 3/H)NBI binds to a nucleoside transporter in brain which specifically recognizes adenosine as its preferred endogenous substrate. This ligand may aid in the identification of CNS neural systems that selectively accumulate adenosine and thereby control adenosinergic function.

• Research Organization: Univ. of Manitoba, Winnipeg, Canada
• OSTI ID: 5483823
• Journal Information: J. Neurosci.; (United States), Journal Name: J. Neurosci.; (United States) Vol. 5:3; ISSN JNRSD
• Country of Publication: United States
• Language: English

Related Subjects

550201* -- Biochemistry-- Tracer Techniques
550501 -- Metabolism-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
ADENOSINE
ANIMALS
AROMATICS
AZAARENES
BIOCHEMICAL REACTION KINETICS
BODY
BRAIN
CENTRAL NERVOUS SYSTEM
ENZYME INHIBITORS
HETEROCYCLIC COMPOUNDS
INOSINE
ISOTOPE APPLICATIONS
KINETICS
LABELLED COMPOUNDS
MAMMALS
MEMBRANE TRANSPORT
NERVOUS SYSTEM
NUCLEOSIDES
NUCLEOTIDES
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANS
PURINES
RATS
REACTION KINETICS
RECEPTORS
RIBOSIDES
RODENTS
TRACER TECHNIQUES
TRITIUM COMPOUNDS
VERTEBRATES