Cadmium and calcium uptake in isolated mitochondria-rich cell populations from the gills of the freshwater rainbow trout

A novel cell isolation technique was used to characterize cadmium and calcium uptake in distinct populations of gill cells from the adult rainbow trout ( Oncorhynchus mykiss). A specific population of mitochondria-rich (MR) cell, termed the PNA(+) MR cell (PNA is peanut lectin agglutinin), was found to accumulate over threefold more Cd-109 than did PNA(-) MR cells, pavement cells (PV cells), and mucous cells during a 1-h in vivo exposure at 2.4 mu g/l Cd-109. In vitro Cd-109 exposures, performed in standard PBS and Cl-- free PBS, at concentrations from 1 to 16 mu g/l Cd-109, were also carried out to further characterize Cd2+ uptake kinetics. As observed during in vivo experiments, PNA(-) MR cells accumulated significantly more Cd-109 than did other cell types when exposures were performed by an in vitro procedure in PBS. Under such conditions, Cd2+ accumulation kinetics in all cell types could be described with Michaelis-Menten relationships, with Km values of similar to 3.0 mu g/l Cd (27 nM) for both MR cell subtypes and 8.6 mu g/l Cd (77 nM) for PV cells. In similar experiments performed in Cl-- free conditions, a significant reduction in Cd-109 accumulation in PNA(-) MR cells was seen but not in PNA(-) MR or in PV cells. In vitro Ca-45 fluxes were also performed to determine the cellular localization of Ca2+ transport in these functionally distinct populations of gill cells. Ca-45 uptake was most pronounced in PNA(-) MR cells, with levels over threefold higher than those found in either PNA(-) MR or in PV cells. Results from the present study suggest that the PNA(+) MR cell type is a high-affinity and high-capacity site for apical entry of Cd2+ and Ca2+ in the gill epithelium of rainbow trout.