Effects of cyclic adenosine 3',5'-monophosphate on photoreceptor disc shedding and retinomotor movement. Inhibition of rod shedding and stimulation of cone elongation.

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Abstract
To test the hypothesis that cyclic nucleotides play a role in the regulation of retinomotor movements and disc shedding in the photoreceptorpigment epithelial complex, an in vitro eyecup preparation, that sustains both disc sheeding and cone retinomotor movement was used. Eyecups were prepared in white light from animals [Xenopus laevis] in which both shedding and cone movement were blocked by 4 d of constant-light treatment. In eyecups incubated for 3 h in light, disc shedding was neglible and cones remained in the light-adapted (contracted) position. In eyecups incubated in darkness, a massive shedding response (dominated by rod photoreceptors) was induced, and at the same time cone photoreceptors elongated to their dark-adapted position. In eyecups incubated in light, db[dibutyryl]cAMP promoted cone elongation and mimicked darkness; the dbcAMP effect was potentiated by the phosphodiesterase inhibitors papaverine and 3-isobutylmethylxanthine. In eyecups incubated in darkness, phosphodiesterase inhibitors and dbcAMP reduced the phagosome content of the pigment epithelium. The effects of dbcAMP on cone elongation and rod sheeding appear specific in that dbcGMP, adenosine, and AMP had no significant effect. Apparently, cAMP plays a role in the regulation of both retinomotor movements and disc shedding.