Brief exposure to light initiates screening pigment migration in retinula cells of the crayfish,Procambarus

Abstract

Exposure of eyes excised from dark-adapted crayfish (Procambarus clarkii) to white light for 30s (Fig. 1) or 5s (Fig. 3) elicits migration of screening pigment in retinula cells; migration continues in the dark without requiring further exposure to light, and reaches completion within 5 to 10 min. For a 5-s exposure to light, the threshold illuminance is about 200 lx and the saturating illuminance is about 20,000 lx (Fig. 2). Between these limits, the extent of migration increases with illuminance, but the rate of migration remains relatively constant (Fig. 3). The calculated velocity of pigment granule transport is about 0.7 μm/s, which is comparable to the velocities reported for much smaller migration distances in some insect eyes.