Characterisation of an uridine-specific binding site in rat cerebrocortical homogenates

• Published in: Neurochemistry international Vol. 43; no. 2; pp. 101 - 112
• Main Authors: Kovács, Ilona, Lasztóczi, Bálint, Szárics, Éva, Héja, László, Sági, Gyula, Kardos, Julianna
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.07.2003; Elsevier
• Subjects: [ [formula omitted]]GTPgammaS binding; [ [formula omitted]]Uridine binding; [ [formula omitted]]Uridine uptake; Adenosine - metabolism; Adenosine and glutamate receptors; Animals; Binding Sites; Binding, Competitive; Biological and medical sciences; Cell Fractionation; Cerebral Cortex - metabolism; Dizocilpine Maleate - pharmacokinetics; Fundamental and applied biological sciences. Psychology; Intracellular Ca 2+ levels; Kainic Acid - pharmacokinetics; Kinetics; Male; Rat brain; Rats; Rats, Wistar; Suramin - metabolism; Synaptic Membranes - metabolism; Synaptic Membranes - ultrastructure; Theophylline - metabolism; Transmembrane Ca 2+ and Na + ion fluxes; Uridine - analogs & derivatives; Uridine - metabolism; Intracellular Ca 2+ levels; Adenosine and glutamate receptors; [ 3 H ]Uridine binding; [ 35 S ]GTPgammaS binding; [ 14 C ]Uridine uptake; Rat brain; Transmembrane Ca 2+ and Na + ion fluxes; Intracellular Ca2+ levels; [35S]GTPgammaS binding: Transmembrane Ca2+ and Na+ ion fluxes; [3H]Uridine binding: [14C]Uridine uptake
• ISSN: 0197-0186; 1872-9754
• DOI: 10.1016/S0197-0186(03)00007-X

Parameters of [ 3 H ]uridine binding to synaptic membranes isolated from rat brain cortex ( K D=71±4 nM, B max=1.37±0.13 pmol/mg protein) were obtained. Pyrimidine and purine analogues displayed different rank order of potency in displacement of specifically bound [ 3 H ]uridine (uridine>5-F-uridine>5-Br-uridine∼adenosine⪢5-ethyl-uridine∼suramin>theophylline) and in the inhibition of [ 14 C ]uridine uptake (adenosine>uridine>5-Br-uridine∼5-F-uridine∼5-ethyl-uridine) into purified cerebrocortical synaptosomes. Furthermore, the effective ligand concentration for the inhibition of [ 14 C ]uridine uptake was about two order of magnitude higher than that for the displacement of specifically bound [ 3 H ]uridine. Adenosine evoked the transmembrane Na + ion influx, whereas uridine the transmembrane Ca 2+ ion influx much more effectively. Also, uridine was shown to increase free intracellular Ca 2+ ion levels in hippocampal slices by measuring Calcium-Green fluorescence. Uridine analogues were found to be ineffective in displacing radioligands that were bound to various glutamate and adenosine—recognition and modulatory—binding sites, however, increased [ 35 S ]GTPgammaS binding to membranes isolated from the rat cerebral cortex. These findings provide evidence for a rather specific, G-protein-coupled site of excitatory action for uridine in the brain.