Specific [ 3H]strychnine binding associated with glycine receptors in bovine retina

Abstract

Saturable, specific [ 3H]strychnine binding can be demonstrated in homogenates of bovine retina. Scatchard plots revealed only one set of binding sites with a dissociation constant ( K d) of about 60 nM and a maximal number of binding sites of about 1.5 pmol/mg protein. The structural specificity of [ 3H]strychnine binding sites in bovine retina parallels the properties found for [ 3H]strychnine binding sites in the spinal cord of several vertebrates. Thus, the data do not give any evidence that specific [ 3H]strychnine binding in bovine retina labels taurine rather than glycine receptors and favors glycine rather than taurine as inhibitory neurotransmitter in bovine retina. The subcellular distribution of specific [ 3H]strychnine binding in bovine retina parallels that of sodium-dependent, high-affinity uptake of glycine and taurine. All 3 parameters are mainly found in the P 2 fractions of bovine retina homogenates, containing conventional synaptosomes, most abundant in the inner plexiform layer, but can also be found in the P 1 fractions, containing large synaptosomes from the photoreceptor cell layer.