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Manganese content and high-affinity transport in liver and hepatoma
T Galeotti1, G Palombini, G D van Rossum
1Istituto di Patologia Generale, Università Cattolica del Sacro Cuore, Rome, Italy.
Abstract:
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.
Insights
Manganese (Mn) uptake differs between normal rat liver and Morris hepatomas. While both tissues possess Mn uptake systems, their specific affinities and capacities do not fully explain the lower endogenous Mn levels observed in hepatomas.
Area of Science:
- Biochemistry
- Cell Biology
- Oncology
Background:
- Morris hepatomas exhibit significantly lower endogenous manganese (Mn) levels compared to normal rat liver.
- Understanding Mn transport mechanisms is crucial for comprehending cellular homeostasis and disease states.
Purpose of the Study:
- To investigate and compare the Mn uptake kinetics in normal rat liver and two Morris hepatoma cell lines (3924A and 9618A).
- To determine if differences in Mn uptake systems explain the reduced endogenous Mn content in hepatomas.
Main Methods:
- Utilized 54Mn radioisotope to measure Mn influx rates in tissue slices.
- Employed atomic absorption spectroscopy to quantify total Mn content.
- Assessed Mn uptake across a concentration range of 0.05 to 100 microM.
Main Results:
- Normal liver displayed three saturable Mn uptake systems with half-maximal rates at approximately 0.075, 2, and 100 microM.
- Hepatoma 3924A showed two systems, with a higher affinity system having a half-maximal rate at 0.34 microM, which is greater than that of liver.
- Hepatoma 3924A exhibited Mn uptake rates equal to or greater than liver across all tested concentrations, while hepatoma 9618A showed slightly lower uptake.
Conclusions:
- Both liver and hepatoma 3924A possess high- and low-affinity Mn uptake systems active at physiological Mn concentrations.
- Observed differences in Mn uptake system kinetics do not fully account for the lower endogenous Mn content in Morris hepatomas compared to normal liver.