Actin‐dependent,Retrograde Motility of Surface‐attached Beads and Aggregating Pigment Granules in Dissociated Teleost Retinal Pigment Epithelial Cells

Teleost retinal pigment epithelial (RPE) cells contain pigment granules within apical projections which undergo actin‐dependent, bi‐directional motility. Dissociated RPE cells in culture attach to the substrate and extend apical projections in a radial array from the central cell body. Pigment granules within projections can be triggered to aggregate or disperse by the presence or absence of 1 mM cAMP. Aminated, fluorescent latex beads attached to the dorsal surface of apical projections and moved in the retrograde direction, towards the cell body. Bead rates on RPE cells with aggregating or fully aggregated pigment granules were 2.2 ± 0.5 and 2.6 ± 0.2 μm/min (mean ± SEM), respectively, similar to rates of aggregating (retrograde) pigment granule movement (2.0 ± 0.4 μm/min). Bead rates were slightly slower on cells with fully dispersed or dispersing pigment granules (1.5 ± 0.1 and 1.5 ± 0.4 μm/min). Movements of surface‐attached beads and aggregating pigment granules were closely correlated in the distal portions of apical projections, but were more independent of each other in proximal regions of the projections. The actin disrupting drug, cytochalasin D (CD), reversibly halted retrograde bead movements, suggesting that motility of surface‐attached particles is actin‐dependent. In contrast, the microtubule depolymerizing drug, nocodazole, had no effect on retrograde bead motility. The similar characteristics and actin‐dependence of retrograde bead movements and aggregating pigment granules suggest a correlation between these two processes.