Uptake of chromate in human red blood cells and isolated rat liver cells: the role of the anion carrier

Abstract

The transport of [⁵¹Cr]chromate into human erythrocytes and isolated rat hepatocytes has been investigated. It was found that uptake in both cell types could be inhibited by the established anion carrier inhibitor 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid. The uptake was very fast, and in kinetic studies a very low K_m was found for both cell types, indicating either a high affinity of chromate for the carrier, and/or, more probably, an efficient intracellular reduction and trapping of ⁵¹Cr. The transport capacity, however, was of the same magnitude as for physiological substrates, such as lactate and sulfate. The uptake was temperature dependent and the activation energy was of the same magnitude as that for the physiological substrates. The uptake could be partly inhibited by high levels (mmol l^–1) of lactate, pyruvate or sulfate. The uptake rate was greatly increased at lower pH (6.0 versus 7.4) which could indicate transport of the HCrO₄– form or an increased intracellular rate of Cr^VI reduction. The results showed efficient uptake of ⁵¹CrO₄²– by erythrocytes and hepatocytes. They were consistent with a mechanism of uptake which involved the cell membrane anion-exchange carrier in the transport and trapping of ⁵¹Cr within the cell.