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 109Cd than did PNA - MR cells, pavement cells (PV cells), and mucous cells during a 1-h in vivo exposure at 2.4 μg/l 109Cd. In vitro 109Cd exposures, performed in standard PBS and Cl --free PBS, at concentrations from 1 to 16 μg/l 109Cd, were also carried out to further characterize Cd 2+ uptake kinetics. As observed during in vivo experiments, PNA + MR cells accumulated significantly more 109Cd than did other cell types when exposures were performed by an in vitro procedure in PBS. Under such conditions, Cd 2+ accumulation kinetics in all cell types could be described with Michaelis-Menten relationships, with K m values of ∼3.0 μg/l Cd (27 nM) for both MR cell subtypes and 8.6 μg/l Cd (77 nM) for PV cells. In similar experiments performed in Cl --free conditions, a significant reduction in 109Cd accumulation in PNA + MR cells was seen but not in PNA - MR or in PV cells. In vitro 45Ca fluxes were also performed to determine the cellular localization of Ca 2+ transport in these functionally distinct populations of gill cells. 45Ca 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 Cd 2+ and Ca 2+ in the gill epithelium of rainbow trout. Copyright © 2006 the American Physiological Society.