Dithiocarbamate-Mediated Uptake of Nickel(II) By Cells In Vitro

Abstract

Dithiocarbamate-mediated nickel(II) uptake was studied in five cell lines: 1) cultured human B-lymphoblasts, 2) rabbit alveolar macrophages, 3) human peripheral lymphocytes, 4) human erythrocytes and 5) human polymorphonuclear leukocytes. Two different incubation protocols were employed: concurrent incubation of nickel(II) with the ligand, and sequential incubation of ligand followed by nickel(II) incubation. The effects of various experimental parameters such as ligand concentration, cell number and available nickel(II) concentration on nickel (II) uptake were examined for most of the above cell types. During concurrent incubations, the effect of ligand concentration on nickel (II) was maximum at 10⁻⁶ M sodium diethyldithiocarbamate (DDC) or ammonium pyrrolidinedithiocarbamate (APDC) for all cell types (except polymorphonuclear leukocytes). Enhanced uptake was evident at higher concentrations (≥ 10⁻³ M DDC or APDC) for sequential incubations. By contrast, ammonium dithiocarbamate (AD) had no enhancing effect on nickel(II) uptake in either protocol (tested only for human peripheral lymphocytes and human erythrocytes). Distribution studies indicated that enhanced cytosolic uptake of nickel(II) occurred for 10⁻⁷ - 10⁻⁵ M DDC. The observed effects on nickel (II) uptake of ligand concentration, Ni² concenration and cell number were interpreted on the basis of an 'Equilibrium Model' with several possible pathways. The nickel(II) uptake data were consistent with the possibility that ligand uptake precedes metal-ion uptake. The latter process may well involve the protonated form of the dithiocarbamate as an ionophore. As a means of enhancing cell-associated nickel(II), peripheral lymphocytes from nickel-sensitized and non-sensitized individuals were pretreated with APDC in veronal buffer. The transforming ability of these cells were then studied by use of a lymphocyte transformation (proliferation) test. This approach was not successful in enhancing the response to nickel (II) because of the inherent toxicities of the veronal buffer and APDC.