Uridine analogue binding sites, the so-called uridine receptor, were observed in the experiments on specific [
3H]N
3-phenacyluridine binding to bovine synaptic membranes using two isomers, N
3-(S)-(+)- and N
3-(R)-(−)-α-hydroxy-β-phenethyluridine, as ligands. The potent hypnotic, N
3-(S)-(+)-α-hydroxy-β-phenethyluridine, but not the (R)-isomer, strongly inhibited [
3H]N
3-phenacyluridine binding. The racemate had inhibitory activity intermediate between that of the two α-hydroxy-β-phenethyluridines ((R)- or (S)-isomers). The inhibitory constants of these compounds were determined. The K
i values of N
3-phenacyluridine, α-hydroxy-β-phenethyluridine (racemate), N
3-(R)-(−)-, and N
3-(S)-(+)-α-hydroxy-β-phenethyluridine were 0.65, 397.4, 1908, and 10.2 nM, respectively. The present results indicate the existence of uridine receptors in the central nervous system in relation to their hypnotic activities reported previously.
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