Characterisation of an uridine-specific binding site in rat cerebrocortical homogenates.
Parameters of [3H]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 [3H]uridine (uridine>5-F-uridine>5-Br-uridine approximately adenosine>>5-ethyl-uridine approximately suramin>theophylline) and in the inhibition of [14C]uridine uptake (adenosine>uridine>5-Br-uridine approximately 5-F-uridine approximately 5-ethyl-uridine) into purified cerebrocortical synaptosomes. Furthermore, the effective ligand concentration for the inhibition of [14C]uridine uptake was about two order of magnitude higher than that for the displacement of specifically bound [3H]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 [35S]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.
Kovács
Ilona
I
Department of Neurochemistry, Chemical Research Center, Hungarian Academy of Sciences, 1025 Pusztaszeri út 59-67, Budapest, Hungary.
Lasztóczi
Bálint
B
Szárics
Eva
E
Héja
László
L
Sági
Gyula
G
Kardos
Julianna
J
D000241:Adenosine / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D001976:Bromouracil / Q000031:analogs & derivatives; D002458:Cell Fractionation; D002540:Cerebral Cortex / Q000378:metabolism*; D016291:Dizocilpine Maleate / Q000493:pharmacokinetics; D007608:Kainic Acid / Q000493:pharmacokinetics; D007700:Kinetics; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D013498:Suramin / Q000378:metabolism; D013570:Synaptic Membranes / Q000378:metabolism* / Q000648:ultrastructure; D013806:Theophylline / Q000378:metabolism; D014529:Uridine / Q000031:analogs & derivatives* / Q000378:metabolism*
D001976:Bromouracil; D013498:Suramin; D016291:Dizocilpine Maleate; D013806:Theophylline; D000241:Adenosine; C006824:5-bromouridine; D007608:Kainic Acid; D014529:Uridine