MAINTENANCE AND INDUCTION IN COCULTURED RAT HEPATOCYTES OF COMPONENTSOF THE CYTOCHROME-P450-MEDIATED MONOOXYGENASE

Hepatocytes grown in culture rapidly lose many of the cytochromes P450 (CYP) responsible for metabolizing foreign compounds. Among the prote ins most readily lost are members of the CYP2B subfamily. We have inve stigated, by RNase protection assays, the ability of rat hepatocytes, cultured conventionally or co-cultured with rat liver epithelial cells , to maintain the expression of genes encoding members of the CYP2B su bfamily, and the inducibility of this expression by phenobarbital. Aft er 4 days of conventional hepatocyte culture CYP2B mRNAs were undetect able, but remained inducible by phenobarbital. In co-cultured hepatocy tes the abundance of the mRNAs remained relatively constant from 4-14 days. After 7 days of co-culture the concentration of the mRNAs was in creased 12-15-fold by phenobarbital. RNase protection assays with prob es capable of distinguishing between CYP2B1 and 2B2 mRNAs demonstrated that the ratios of the abundance and inducibility of the two mRNAs we re the same in co-culture as in vivo. Co-cultured hepatocytes also mai ntained the expression of genes coding for two other components of the cytochrome P450-mediated mono-oxygenase, namely cytochrome P450 reduc tase and cytochrome b5.