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Investigative Ophthalmology & Visual Science, Vol 35, 178-188, Copyright © 1994 by Association for Research in Vision and Ophthalmology

ARTICLES AND REPORTS

Suppression of cAMP-induced pigment granule aggregation in RPE by organic anion transport inhibitors

DM Garcia and B Burnside
Department of Molecular and Cell Biology, University of California, Berkeley 94720.

PURPOSE. To investigate the mechanism(s) by which intracellular cAMP levels are elevated to induce pigment granule aggregation in teleost retinal pigment epithelium (RPE). METHODS. Pigment granule migration was studied in vitro using RPE sheets isolated from dark-adapted green sunfish, Lepomis cyanellus. After preculture to allow pigment granule dispersion, RPE sheets were incubated with various agents to test their ability to induce pigment granule aggregation. RPE sheets were then fixed, and pigment granule position was assessed microscopically. RESULTS. Pigment granule aggregation was induced by nonderivatized cAMP. At maximally effective concentration (1 mM), cAMP was as effective as its more membrane-permeant analogs dbcAMP and 8-Br-cAMP. Forskolin (1 or 10 microM), a stimulator of adenylyl cyclase, was also effective at inducing pigment aggregation. Two inhibitors of organic anion transport, probenecid and sulfinpyrazone, inhibited cAMP-induced aggregation by approximately 80% but had no effect on forskolin-induced aggregation. Several agents shown to stimulate RPE adenylyl cyclase in other species failed to induce pigment aggregation in isolated RPE sheets. CONCLUSIONS. Our observations strongly suggest that exogenously applied, nonderivatized cAMP can gain access to the cytoplasm of isolated RPE cells via organic anion transporters. Thus, if cAMP were secreted by retinal cells into the subretinal space, it could be taken up by RPE cells and subsequently act as an intracellular messenger to activate dark-adaptive physiological processes such as pigment granule aggregation.


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 J. Cell Sci.Home page
C King-Smith, P Chen, D Garcia, H Rey, and B Burnside
Calcium-independent regulation of pigment granule aggregation and dispersion in teleost retinal pigment epithelial cells
J. Cell Sci., January 1, 1996; 109(1): 33 - 43.
[Abstract] [PDF]


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Copyright © 1994 by the Association for Research in Vision and Ophthalmology