Research article

Uptake of ³H-cAMP by retinal pigment epithelium isolated from bluegill sunfish (Lepomis macrochirus)

Thomas A Keith , Varsha Radhakrishnan , Steve Moredock and Dana M García

Department of Biology, Texas State University-San Marcos, San Marcos, Texas 78666, USA

author email corresponding author email

BMC Neuroscience 2006, 7:82doi:10.1186/1471-2202-7-82

Published:	29 December 2006

Abstract

Background

In bluegill sunfish, the melanin-containing pigment granules of the retinal pigment epithelium undergo cyclic movements in response both to ambient lighting and circadian cues. Pigment granules aggregate into the cell body at night (in the dark), and disperse into apical processes during the day (in the light). Regulation of pigment granule aggregation in a number of fishes depends on modulating the intracellular levels of cyclic adenosine monophosphate.

Results

Here we show isolated RPE takes up cyclic adenosine monophosphate (cAMP) in a saturable manner, exogenously applied cAMP induces pigment granule aggregation in retinal pigment epithelium isolated from bluegill, and aggregation induced in this manner is inhibited by treatment with probenecid, an organic anion transport inhibitor.

Conclusion

Our results raise the possibility that cAMP functions as a messenger secreted from the neural retina to signal darkness to the RPE, which takes it up. It further suggests that organic anion transport systems are the route by which cAMP crosses RPE cell membranes since probenecid inhibits extracellular cAMP from causing pigment granule aggregation.