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, Sesarma cinereum. Isolated crab eyes (eyecup plus eyestalk) were maintained in crustacean Ringer either prepared normally or calcium-free plus 50 mM EGTA. Pigment granule movement was indirectly observed by monitoring 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 centripetal migration of pigment granules (normally leading to pupillary closure), and photoreceptors eventually became locked in the open-pupil, dark-adapted state despite repeated stimuli. In contrast, ERG responses continued throughout EGTA treatment, although the size and shape of the response was altered. Normal ERG responses and pigment granule movements returned after replacing EGTA-Ringer with normal-calcium medium. These results suggest that centripetal migration of pigment granules in crustacean photoreceptors requires calcium.
King-Smith
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Department of Biological Sciences, University of Maryland-Baltimore County 21228, USA.
Cronin
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D000818:Animals; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D003386:Brachyura / Q000502:physiology*; D002118:Calcium / Q000502:physiology; D004533:Egtazic Acid; D004596:Electroretinography; D066298:In Vitro Techniques; D017956:Photoreceptor Cells, Invertebrate / Q000187:drug effects / Q000502:physiology; D012025:Reflex, Pupillary / Q000187:drug effects / Q000502:physiology; D012168:Retinal Pigments / Q000502:physiology
D012168:Retinal Pigments; D004533:Egtazic Acid; D002118:Calcium