title: Toxic and teratologic effects of verapamil on early chick embryos: evidence for the involvement of calcium in neural tube closure.
abstract: Toxic and teratologic effects of verapamil, a calcium antagonist, on chick embryos explanted at stage 8 (four-somite stage) and cultured for 6-8 hours were investigated. In general, embryos responded to verapamil in a dose-related manner. Concentrations lower than 2 micrograms/ml had no apparent effect on the development of embryos. A concentration of 15 micrograms/ml significantly increased the incidence of embryos (approximately 80% of viable embryos) with neural tube closure defects and less numerous somites. Higher concentrations (e.g., 30 micrograms/ml) were embryotoxic and over 90% of the embryos were either severely malformed or dead after 8 hours of incubation. Compared to controls, verapamil-treated neuroepithelial cells had smoother apical surfaces and less conspicuous microfilament bundles. The deleterious effects of verapamil (15 micrograms/ml) could be reversed by subculturing the affected embryos, within 3 hours of treatment, on nutrient medium alone or on nutrient medium containing 25 micrograms/ml chlorotetracycline (CTC), a calcium agonist, the latter being more effective provided that treatment did not exceed 4 hours. Exposure of the developing neuroepithelium to 15 micrograms/ml verapamil for 3-4 hours resulted in a significant reduction in free Ca2+ levels, as revealed by the pyroantimonate precipitation method, throughout neuroepithelial cells. Overall results suggest that verapamil causes neural tube closure defects by reducing intracellular free Ca2+ levels, thereby relaxing apical microfilament bundles of developing neuroepithelial cells.
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002642:Chick Embryo; D005865:Gestational Age; D007473:Ion Channels / Q000378:metabolism; D009436:Neural Tube Defects / Q000139:chemically induced* / Q000473:pathology; D013723:Teratogens; D014700:Verapamil / Q000633:toxicity*
chemical_list: D007473:Ion Channels; D013723:Teratogens; D014700:Verapamil; D002118:Calcium