[H-3]spermine binding to synaptosomal membranes from the chick retina

The binding of [H-3]spermine to synaptosomal membranes from chick retina wa s examined. Saturable specific binding of [H-3]spermine to synaptosomal mem branes from plexiform layers of retina (P-1 and P-2) has been characterized , and found to concentrate in the inner plexiform layer compared to the out er plexiform layer (B-max = 9.3 and 37 pmol/mg protein for P-1 and P-2, res pectively). Kinetics of specific [H-3]spermine binding yield a sigmoidal sa turation curve, indicating positive cooperativity (nH: 2.4 and 3.2 for P-1 and P-2, respectively) with high affinity: K-app = 61 and 67 nM for P-1 and P-2. The time required to attain equilibrium at room temperature was less than 5 min in both fractions. Dose-response curves for spermine, spermidine , and diethylene-triamine (DET) show different potencies for inhibiting [H- 3]spermine binding: spermine > spermidine > DET. Our results support a role for polyamines (PA) as neurotransmitters or neuromodulators in the vertebr ate retina. (C) 1999 Published by Elsevier Science B.V. All rights reserved .