³H-flunitrazepam binding to bovine retina and the effect of GABA thereon

Bovine retinae were examined for their ability to bind ³H-flunitrazepam. Whole retinal homogenates revealed specific, high affinity, and saturable ³H-flunitrazepam binding (K_d, 1.1 nM; B_max, 19.5 fmoles/mg tissue). In washed membrane preparations, 10 μM GABA caused a dramatic decrease in the K_d (42 percent). The rank order of potency for the inhibition of ³H-flunitrazepam binding by different benzodiazepines was: clonazepam > clobazam ≫ Ro 5-4864. These results are supportive for the presence of benzodiazepine receptors in the bovine retina and indicate a likeness with the previously described benzodiazepine receptors of mammalian brain.