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 PN[A.sup.+] MR cell (PNA is peanut lectin agglutinin), was found to accumulate over threefold more [sup.109]Cd than did PN[A.sup.-] MR cells, pavement cells (PV cells), and mucous cells during a 1-h in vivo exposure at 2.4 [micro]g/1 [sup.109]Cd. In vitro [sup.109]Cd exposures, performed in standard PBS and [Cl.sup.-]- free PBS, at concentrations from 1 to 16 [micro]g/1 [sup.l09]Cd, were also carried out to further characterize [Cd.sup.2+] uptake kinetics. As observed during in vivo experiments, PN[A.sup.+] MR cells accumulated significantly more [sup.109]Cd than did other cell types when exposures were performed by an in vitro procedure in PBS. Under such conditions, [Cd.sup.2+] accumulation kinetics in all cell types could be described with Michaelis-Menten relationships, with [K.sub.m] values of ~3.0 [micro]g/l Cd (27 nM) for both MR cell subtypes and 8.6 [micro]g/1 Cd (77 nM) for PV cells. In similar experiments performed in [Cl.sup.-]-free conditions, a significant reduction in [sup.109]Cd accumulation in PN[A.sup.+] MR cells was seen but not in PN[A.sup.+] MR or in PV cells. In vitro [sup.45]Ca fluxes were also performed to determine the cellular localization of [Ca.sup.2+] transport in these functionally distinct populations of gill cells. [sup.45]Ca uptake was most pronounced in PN[A.sup.+] MR cells, with levels over threefold higher than those found in either PN[A.sup.-] MR or in PV cells. Results from the present study suggest that the PN[A.sup.+] MR cell type is a high-affinity and high-capacity site for apical entry of [Cd.sup.2+] and [Ca.sup.2+] in the gill epithelium of rainbow trout. freshwater fish gill epithelium; peanut lectin agglutinin; metal binding; MINEQL+