Binding of 3H-ADTN, a dopamine agonist, to membranes of the bovine retina.

The binding of 3H-ADTN, a potent dopamine receptor agonist, to crude membrane preparations of bovine retina was studied, using a filtration method to isolate membrane-bound ligand. Specific binding was found to be saturable and occurred at a single binding site with an affinity constant of 7.3 nM. Binding was sodium-independent, slightly enhanced by Triton X-100 treatment, but drastically reduced by both trypsin and sodium laurylsulphate. The binding sites demonstrated a high degree of pharmacological specificity, with dopamine, apomorphine, and epinine being potent displacers of 3H-ADTN. A higher degree of 3H-ADTN binding was associated with subcellular fractions enriched with conventional synaptosomes rather than fractions enriched with photoreceptor synaptosomes.