title: Photoreceptor disc shedding in eye cups. Inhibition by deletion of extracellular divalent cations.
abstract: To further define the medium requirements for in vitro rod disc shedding and phagocytosis in eye cups of Xenopus laevis, the effect of deletion of divalent cations was examined. Calcium-free medium completely eliminated both normal diurnal disc shedding (initiated by light onset) and dark-primed disc shedding (initiated by a period of darkness followed by additional darkness or light). The effect was reversible. Furthermore, the events that occurred during the initial dark-priming period did not require extracellular millimolar calcium, since the addition of calcium (1.8 mM) after an initial hour of darkness in calcium-free medium resulted in a marked increase in disc shedding, regardless of the subsequent lighting condition. Magnesium-free medium did not inhibit light-evoked shedding. However, magnesium-free medium partially inhibited disc shedding in one of the two lighting paradigms used to elicit dark-primed disc shedding. This suggests that the extracellular divalent cation requirement varies for different lighting paradigms that promote shedding. The inhibition of disc shedding by magnesium-free medium was morphologically distinct from calcium-free medium; the inhibition in magnesium-free medium was correlated uniquely with a reduction in the interdigitation between the photoreceptor and the retinal pigment epithelium.
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D003470:Culture Media; D066298:In Vitro Techniques; D008274:Magnesium / Q000378:metabolism / Q000494:pharmacology; D010587:Phagocytosis / Q000187:drug effects; D010786:Photoreceptor Cells / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D014982:Xenopus laevis
chemical_list: D003470:Culture Media; D008274:Magnesium; D002118:Calcium