EMBRYOTOXIC POTENCY OF 2,4,5-TRICHLOROPHENOXYACETIC ACID ON SEA-URCHIN EGGS - ASSOCIATION WITH CALCIUM HOMEOSTASIS

The effect of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), a polychlor inated herbicide, on the early development of sea urchin eggs and on C a2+ permeability was investigated. Concentrations lower than 5 x 10(-4 ) M delayed the first cleavages and produced a teratogenic effect char acterized by a large spectrum of structural malformations at the plute us stage. The cleaving stage (pre-hatching) was the period most sensit ive to the compound. Upper concentrations caused a stepwise dose-depen dent lethality associated with arrest of cleavage. 2,4,5-T increased p lasmalemma Ca2+ permeability of unfertilized eggs by opening voltage-d ependent Ca2+ channels; verapamil (10(-4) M) and nifedipine (10(-4) M) abolished this effect. Ca2+ permeability was also increased by 2,4,5- T after fertilization of the eggs. ATP-dependent intracellular sequest ration of Ca2+, measured in isolated cortices, was inhibited by 2,4,5- T. Ca2+ movement was affected over a range of concentrations similar t o those producing embryonic abnormalities and lethality. The results s uggest that the teratogenic potency of 2,4,5-T is associated with dela y in first cleavages and alterations in Ca2+ homoeostasis.