Human placental Ca2+-ATPase: in vitro inhibition by DDT homologs.

Abstract In vitro inhibition of Ca 2+ -ATPase by DDT homologs was studied using maternal brush-border membranes from human term placentas as an enzyme source. At 10 μM concentration many of the compounds tested inhibited this enzyme. The order of effectiveness of inhibition was as follows: p , p ′-DDE> p , p ′-DDD> p , p ′-DDT> methoxychlor(mec). Both p , p ′-DDOH and p , p ′-DDA did not inhibit the placental Ca 2+ -ATPase. Assays using varying concentrations (0.3 μM to 0.1 mM) of p , p ′-DDT were also performed. The inhibition of human placental Ca 2+ -ATPase ranged from 12% for 0.3 μM p,p p , p ′-DDT to 69% for 30 μM p , p ′-DDT. Higher concentrations of this pesticide failed to cause further enzyme inhibition.