Capacitative Ca2+ influx in the neural retina of chick embryo

Depletion of intracellular Ca2+ stores induces a capacitative Ca2+ influx in non-neural cells. It has been unknown whether the capacitative Ca2+ influx occurs in the cells of nervous systems. We found the capacitative Ca2+ influx in the neural retina of early embryonic chick with Fura-2 fluorescence measurements. A Ca(2+)-free medium containing thapsigargin (500 nM), an inhibitor of Ca(2+)-ATPase of intracellular Ca2+ stores, was applied to the neural retina of embryonic day 3 (E3) chick. A rise in intracellular Ca2+ concentration was evoked after the reintroduction of extracellular Ca2+, and this Ca2+ rise was suppressed by Zn2+ (1 mM) and Ni2+ (5 mM). The developmental changes in the Ca2+ rise induced by thapsigargin (250 nM) were studied from E3 to E13. The thapsigargin-induced Ca2+ rise was largest at E3, declined rapidly toward E6, and then decreased gradually until E13, when the Ca2+ rise almost disappeared. This developmental profile correlated with the decline in the mitotic activities of the retinal cells studied by Prada et al. The fluorescence imaging with the vertical slice of the E9 retina showed that the site at which the thapsigargin-induced Ca2+ rise was largest was the most outer layer of the retina, where proliferating cells are located. This spatial distribution and the above developmental profile may suggest that the capacitative Ca2+ influx occurs at the early period of neurogenesis when the cells have mitotic activities.