Depression of the Ca(2+)-ATPase activity of the rat liver endoplasmic reticulum by the liver tumour promoters, 1,1,1-trichloro-2,2-bis(p-chlorophenyl)-ethane and phenobarbital.

The effects of a short-term in vivo administration of two liver tumour promoters (phenobarbital and 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane on rat liver endoplasmic reticulum Ca(2+)-ATPase were investigated. The specific activity values of this membrane-bound enzyme significantly decreased (P less than 0.01) by 51% for phenobarbital-treated rats and by 48% for 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane-treated rats compared with control animals. The depression of liver endoplasmic reticulum Ca(2+)-ATPase appears to be a manifestation of the toxicological effect of tumour promoters.