The binding of somatostatin to the mouse retina is altered by the pearl mutation

Abstract

Pearl mutants have a night-blind phenotype and abnormal optokinetic nystagmus. Preliminary results from another study showed that the light responses of retinal ganglion cells of pearl mutant mice were affected by bathing the isolated retina with low (less than 1 nM) concentrations of either somatostatin-14 or -28, whereas the responses in wild-type retinas were affected only by somatostatin-28. In order to test the possibility that these physiological differences resulted from alterations in receptor affinity, we studied the binding of 125I-[Tyr11]-somatostatin-14 and 125I-[Leu8,D-Trp22,Tyr25]-somatostatin-28 to frozen, unfixed sections of eyes of wild-type (C57BL/6J +/+) and congenic pearl mutant (C57BL/6J-pin pe(pin)/pe(pin)) mice. As found previously for wild-type mice, specific binding occurred in 3 maxima in pearl mutants: a broad band extending from the retinal ganglion cell to the inner nuclear layer, a narrow and inconstant band over the outer plexiform layer, and a band over the pigment epithelium and choroid. We quantified the label over the inner plexiform layer and found evidence for a single saturable site in both genotypes. However, several results indicate that somatostatin-14 binds more avidly to pearl mutant retinas than to wild-type retinas. In saturation binding studies, Kd for 125I-[Tyr11]-somatostatin-14 was 600 pM in pearl mutants vs 1.5 nM in wild-type; whereas, for 125I-[Leu8,D-Trp22,Tyr25]-somatostatin-28, Kd was nearly equal in the two genotypes (500 and 625 pM, respectively). Bmax was nearly equal for both ligands in both genotypes (63-69 fmol/mg protein).(ABSTRACT TRUNCATED AT 250 WORDS)