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COMPARATIVE AND EVOLUTIONARY PHYSIOLOGY

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

Department of Biology, McMaster University, Hamilton, Ontario, Canada

Submitted 28 March 2005 ; accepted in final form 24 January 2006

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 Cd²⁺ 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, Cd²⁺ 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 Ca²⁺ 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 Cd²⁺ and Ca²⁺ in the gill epithelium of rainbow trout.

freshwater fish gill epithelium; peanut lectin agglutinin; metal binding; MINEQL+

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