Manganese content and high-affinity transport in liver and hepatoma.

Morris hepatomas 3924A and 9618A have much lower endogenous contents of Mn than normal rat liver. This work studied the uptake of Mn by slices of these three tissues over a range of concentrations from 0.05 to 100 microM. The influx was assessed with 54Mn while atomic absorption measurements determined the total content. At medium Mn from 0.05 to 5 microM, entry of 54Mn in 2 min was taken as the initial rate and within this period the apparent concentration of Mn in the cell water exceeded that in the medium. Liver showed three apparently saturable uptake systems, the medium concentrations of Mn for half-maximal uptake rate being 0.075, approximately 2, and 100 microM. Hepatoma 3924A appeared to have only two systems, the half-maximal concentration for the higher affinity mechanism being, at 0.34 microM, substantially greater than that for liver. At no concentration was the uptake rate of Mn by hepatoma 3924A less than that of liver although there was some indication that Mn uptake by 9618A was somewhat less than that by the other two tissues. It is concluded that liver and hepatoma 3924A have systems for Mn uptake with affinities that enable them to be active at the plasma concentration (approximately 0.1 microM) as well as uptake systems of less affinity. However, differences in these systems between liver and hepatomas do not account for the differences in endogenous Mn content.