Ja. Perezleon et R. Salceda, DIFFERENT SPECIFIC BINDING-SITES OF [H-3] GLYCINE AND [H-3] STRYCHNINE IN SYNAPTOSOMAL MEMBRANES ISOLATED FROM FROG RETINA, Neurochemical research, 20(8), 1995, pp. 915-922
Synaptosomal fractions were isolated from frog retina: a fraction enri
ched in photoreceptor terminals (P1) and a second one (P2) containing
interneurons terminals. We compared the binding of [H-3]glycine and [3
H]strychnine to membranes of these synaptosomes. The binding of both r
adioactive ligands was saturable and Na+-independent. [H-3]Glycine bou
nd to a single site in P1 and P2 synaptosomal fractions, with K-D = 12
and 82 nM and B-max = 3.1 and 3.06 pmol/mg protein respectively. [H-3
]Strychnine bound to two sites in each one of the synaptosomal fractio
ns. For P1 K-D values were 3.9 and 18.7 nM, and B-max values were 1.1
and 7.1 pmol/mg protein, respectively. Membranes from the P2 synaptoso
mal fraction showed K-D's of 0.6 and 48 nM and B-max's of 0.4 and 4.5
pmol/mg. Specific [H-3]glycine binding was displaced by beta-alanine,
I-serine, d-serine and HA966, but not by strychnine, 7-chlorokynurenic
or 5,7-dichloro-kynurenic acids. Specific [H-3]strychnine binding was
partially displaced by glycine and related aminoacids and totally dis
placed only by 2-NH2-strychnine. Our results indicate the presence of
high affinity binding sites for glycine and strychnine in frog retinal
synaptosomal membranes. The pharmacological binding pattern indicates
the presence of the strychnine sensitive glycine receptor as well as
other sites. These might not include the NMDA receptor-associated glyc
ine site.