Autoradiographic distribution of forskolin and phorbol ester binding sites in the retina.

We have localized the distribution of [3H]forskolin and [3H]phorbol dibutyrate binding sites autoradiographically in the rat, monkey, and human retina. In the rat and monkey retina, forskolin binding was enriched in the inner plexiform layer, in the inner and outer segments of the photoreceptors, and in the retinal pigment epithelium. In the human retina, forskolin binding sites were uniformly distributed and higher in density. Forskolin binding was also detected over the ciliary body, the ciliary epithelium, and the iris sphincter. The distribution of phorbol ester binding sites was similar in the rat, monkey, and human retina. The inner plexiform layer contained the highest density followed by the inner nuclear and outer plexiform layers, and the ganglion cell layer. In the rat, phorbol ester binding was present in the iris, the ciliary body, and the ciliary epithelium. The monkey and human ciliary body also contained a low density of phorbol ester binding sites.