Cadmium and calcium transport along the gastro-intestinal tract of rainbow trout : more than “gut feelings” on mechanisms of uptake
Date
2011-10
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Biology Department, McMaster University, Hamilton, ON, CA
Abstract
Teleosts take up metals by two major pathways: gills and/or gut. Past research is
heavily focused on branchial uptake despite evidence that the gastro-intestinal tract (GIT)
is the dominant route in some natural environments. To address this information gap, my
thesis characterizes uptake mechanisms of Cd and Ca along the GIT of Oncorhynchus
mykiss. Toxic effects of Cd, protective effects of Ca against Cd uptake, and Cd
distribution within fish after ingestion are also explored.
Four-week dietary Cd exposure affected growth and Ca regulation, while causing
toxicity at the subcellular level. Elevated Ca in diets protected against accumulation and
altered subcellular handling of Cd. Pre-exposure to different diets changed unidirectional
uptake and binding rates of Cd and Ca, although they remained highly correlated. Binding
rates of Cd to mucus can predict absorption rates of Cd.
A variety of in vitro and in vivo experiments on four distinct GIT segments
(stomach, anterior-, mid-, and posterior- intestine) were undertaken to determine specific
mechanisms of Cd and Ca uptake in freshwater trout. Cd transport was unaffected by
solvent drag, but was stretch- and temperature- sensitive. Strong evidence for a common
pathway for Ca and Cd transport was obtained. Cd also appeared to be taken up in part by
zinc (ZIP-like) transporters and the divalent metal transporter DMT1. Ca uptake along the
GIT appeared to be carrier-mediated, time- and concentration- dependent, but was not
affected by solvent drag, or by Na concentration. Mucosal Cd did not inhibit Ca uptake.
Ca, but not Cd, uptake rates were much lower in sea water-acclimated trout. Seawater and
freshwater fish accumulated similar whole body Cd concentrations when fed
contaminated diets for three weeks, but the majority of Cd in seawater trout remained in
the posterior intestine tissue, while freshwater trout had higher internal burdens.
This thesis advances the knowledge of metal uptake along the GIT of trout.
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Keywords
PHARMACOLOGY, MOLECULAR MECHANISMS OF PHARMACOLOGICAL ACTION, GASTROINTESTINAL TRACT, FISH PHYSIOLOGY, CALCIUM, CADMIUM, ZINC TRANSPORTER