CHARACTERIZATION OF [I-125] TYR11-SOMATOSTATIN BINDING-SITES IN THE RABBIT RETINA

We have identified specific receptors for somatostatin (SS) in the rabbit retina using the radioligand [I-125]Tyr11-Somatostatin. [I-125]Tyr11-SS bound with high affinity to retinal membranes as was ascertained by both kinetic and saturation experiments. Scatchard analysis of the saturation data for [I-125]Tyr11-SS binding to retinal membranes suggest a single population of sites with an apparent affinity constant (K(D)) of 0.90 +/- 0.20nM and a maximum number of binding sites (B(max)) of 104 +/- 52 fmol/mg protein. The specific binding of [I-125]Tyr11-SS was displaced in a dose-dependent manner by SS, Tyr11-SS, SMS 201-995, SS-28 and D-Trp8-SS. The inactive SS analog SS28(1-14) as well as the peptides CRF and bombesin had no effect. In addition, the specific binding of [I-125]Tyr11-SS was attenuated by GTPgS. These findings demonstrate the presence of a selective receptor for SS in the rabbit retina that is coupled to guanine nucleotide binding protein(s).