PIGMENT GRANULE MIGRATION IN CRUSTACEAN PHOTORECEPTORS REQUIRES CALCIUM

We have investigated the role of calcium in the regulation of pigment granule migration in photoreceptors of the semi-terrestrial crab, Sesa rma cinereum. Isolated crab eyes (eyecup plus eyestalk) were maintaine d in crustacean Ringer either prepared normally or calcium-free plus 5 0 mM EGTA. Pigment granule movement was indirectly observed by monitor ing reflectance from the eye during light stimuli using intracellular optical physiological techniques. Electroretinograms (ERGs) were also measured during light stimuli. EGTA treatment caused gradual loss of c entripetal migration of pigment granules (normally leading to pupillar y closure), and photoreceptors eventually became locked in the open-pu pil, dark-adapted state despite repeated stimuli. In contrast, ERG res ponses continued throughout EGTA treatment, although the size and shap e of the response was altered. Normal ERG responses and pigment granul e movements returned after replacing EGTA-Ringer with normal-calcium m edium. These results suggest that centripetal migration of pigment gra nules in crustacean photoreceptors requires calcium.