title: Spermine inhibits [3H]glycine binding at the NMDA receptors from plexiform layers of chick retina.
abstract: Saturable specific binding of glycine to synaptosomal membranes from plexiform layers of the retina has been described, which seems to correspond to the modulatory site on NMDA-receptors (26). Spermine inhibited specific [3H]glycine binding to membranes from synaptosomal fractions from the outer (P1) and the inner (P2) plexiform layers of 1-3 day-old chick retinas in a dose-dependent manner with an IC50 = 35 microM for the P1 fraction and 32 microM for the P2 fraction. Kinetic experiments and non-linear regression analysis of [3H]glycine-specific binding showed a Kd approximately 100-150 nM in both fractions, and a higher Bmax (4.11 +/- 0.47 pmol/mg protein) for the inner plexiform layer compared to the outer plexiform layer (Bmax = 2.76 +/- 0.25 pmol/mg protein). Strychnine-insensitive [3H]glycine binding was inhibited by 100 microM spermine, due to a reduction in Bmax (P1 = 0.84 +/- 0.16 pmol/mg protein; P2 = 0.81 +/- 0.16 pmol/mg protein) without affecting the Kd. Association and dissociation constants in the absence and presence of 50 microM spermine remained unchanged. Results demonstrate the presence of a single modulatory site for spermine on NMDA receptors, in both synaptic layers of the chick retina.
authors.affiliation: Instituto de Fisiología Celular, Departamento de Neurociencias, Universidad Nacional Autonoma de México, México, DF.
authors.forename: F
authors.initials: F
authors.lastname: Calderón
authors.forename: A M
authors.initials: AM
authors.lastname: López-Colomé
mesh_terms: D000818:Animals; D002645:Chickens; D004305:Dose-Response Relationship, Drug; D005998:Glycine / Q000378:metabolism*; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism*; D012160:Retina / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure; D013096:Spermine / Q000494:pharmacology*; D013574:Synaptosomes / Q000187:drug effects* / Q000378:metabolism; D014316:Tritium
chemical_list: D016194:Receptors, N-Methyl-D-Aspartate; D014316:Tritium; D013096:Spermine; D005998:Glycine