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

In vitro inhibition of Ca2+-ATPase by DDT homologs was studied using maternal brush-border membranes from human term placentas as an enzyme source. At 10 microM concentration many of the compounds tested inhibited this enzyme. The order of effectiveness of inhibition was as follows: p,p'-DDE greater than p,p'-DDD greater than p,p'-DDT greater than methoxychlor(mec). Both p,p'-DDOH and p,p'-DDA did not inhibit the placental Ca2+-ATPase. Assays using varying concentrations (0.3 microM to 0.1 mM) of p,p'-DDT were also performed. The inhibition of human placental Ca2+-ATPase ranged from 12% for 0.3 microM p,p'-DDT to 69% for 30 microM p,p'-DDT. Higher concentrations of this pesticide failed to cause further enzyme inhibition.