Figure 4

RPE cells with pigment aggregated and dispersed. Phase contrast images illustrate RPE with pigment granules aggregated in response to treatment with 1 mM cAMP (left) and RPE with pigment granules dispersed as a consequence of inhibition of cAMP-induced aggregation by probenecid (0.5 mM; right). Dotted lines indicate the position of the base of the cell, and the thin, diagonal arrow indicates the position of the end of the longest apical process for the same cell. For the cAMP-treated cells, a thick, horizontal arrow indicates the position of the distal-most pigment granule; for the probenecid-treated cells, that position corresponds with the end of the process. Scale bar equals 50 μm.