Chemical modification of membrane proteins by brominated taurodehydrocholate in isolated hepatocytes; relationship to the uptake of cholate and of phalloidin and to the sensitivity of hepatocytes to phalloidin.

In vitro treatment of isolated rat hepatocytes with brominated taurodehydrocholic acid (BTC) reduced their sensitivity against phalloidin and inhibited the uptake of phalloidin as well as of cholate in an irreversible and concentration dependent manner. BTC was taken up itself by liver cells; this process was inhibited by 4,4'-diisothiocyano 2,2'-stilbene disulfonate (DIDS). When hepatocytes were incubated with 35S-BTC their plasma membranes contained five labeled protein species with molecular weights of 67,000, 49,000, 38,000, 32,000 and 24,000 as shown by SDS-electrophoresis. No marked difference was observed when isolated plasma membranes from livers were directly treated with the affinity label. DIDS suppressed covalent binding of 35S-BTC to membrane components drastically. Incubation of phalloidin insensitive AS-30D ascites hepatoma cells with 35S-BTC did not result in a chemical modification of the above five proteins. This agrees with an earlier observation that hepatoma cells are unable to take up phalloidin and bile acids (Petzinger et al. 1979; Rufeger and Grundmann 1977; Kroker et al. 1978).