Department of Biology, Rutgers University, Camden, NJ 08102.
Intracellular free calcium ion (Ca2+) levels of the developing chick neuroepithelium during neural tube closure (Hamburger and Hamilton stages 3-11 of embryonic development) were determined using the hydrophobic acetoxymethyl ester of the fluorescent dye fura-2 (fura-2/AM). Temporal changes in the free Ca2+ level in neuroepithelial cells are correlated with the degree of folding of the neuroepithelium. The concentration of intracellular Ca2+ in the neuroepithelium reaches its highest level when apposing neural folds are actively making contact.