Physiological action of dissolved organic matter in rainbow trout in the presence and absence of copper: Sodium uptake kinetics and unidirectional flux rates in hard and softwater
We investigated the physiological effects of dissolved organic matter (DOM) on sodium (Na +) transport in juvenile Oncorhynchus mykiss (∼2.5 g) in the presence and absence of simultaneous acute exposure to copper (Cu 2+; 0, 70, and 300 μg l −1). Trout were acclimated in either hardwater (∼1000 μM Ca...
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Published in | Aquatic toxicology Vol. 70; no. 1; pp. 63 - 81 |
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Main Authors | , , , |
Format | Journal Article |
Language | English |
Published |
Amsterdam
Elsevier B.V
18.10.2004
Elsevier Science |
Subjects | |
Online Access | Get full text |
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Summary: | We investigated the physiological effects of dissolved organic matter (DOM) on sodium (Na
+) transport in juvenile
Oncorhynchus mykiss (∼2.5
g) in the presence and absence of simultaneous acute exposure to copper (Cu
2+; 0, 70, and 300
μg
l
−1). Trout were acclimated in either hardwater (∼1000
μM Ca
2+) or softwater (∼100
μM Ca
2+), and DOM was tested at approximately 8
mg
C
l
−1 using a natural (NOM) and a commercial (AHA) source. Ion transport was evaluated based on kinetics estimates (maximum Na
+ uptake rates,
J
max; substrate affinity,
K
m) and unidirectional flux measurements (
J
in,
J
out,
J
net).
J
max was higher and unidirectional flux rates were greater in softwater-acclimated trout. Fish exposed to DOM alone in hardwater exhibited an increased Na
+ transport capacity indicated by both the kinetics (67% higher
J
max for AHA) and
J
in measurements (153% higher for AHA and 125% higher for NOM). In softwater, the effects of DOM alone on kinetic parameters and unidirectional flux rates were negligible. Cu
2+ affected Na
+ uptake by a mixed-type inhibition (both non-competitive and competitive). In hardwater, only
K
m was increased (i.e., affinity decreased), whereas in softwater,
K
m was increased and
J
max was decreased, with more marked effects at the higher Cu
2+ level. In hardwater, the stimulatory effect of AHA on
J
max persisted even in the presence of 300
μg
l
−1 Cu
2+, whereas both AHA and NOM prevented the increase in
K
m caused by Cu
2+; these effects were reflected in
J
in measurements. In softwater, AHA helped to protect against the increased
K
m caused by high Cu
2+, but there was no protection against the inhibition of
J
max. Unidirectional flux measurements indicated that in softwater, Cu
2+ inhibited
J
in at 70
μg
l
−1, whereas at 300
μg
l
−1 Cu
2+,
J
out was also stimulated. Fish were more affected by Cu
2+ in softwater, as indicated by the inability to control diffusive losses of Na
+ and a reduced ability to take up Na
+, but in the presence of DOM, losses were better controlled at the end of 6
h exposure. We conclude that DOM has direct effects on the gills, as well as protecting fish against acute Cu
2+ toxicity. This occurs because DOM complexes Cu
2+, and because it acts on the transport and permeability properties of the gills. These effects differ depending on both water hardness and the nature of the DOM source. |
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Bibliography: | ObjectType-Article-2 SourceType-Scholarly Journals-1 ObjectType-Feature-1 content type line 23 ObjectType-Article-1 ObjectType-Feature-2 |
ISSN: | 0166-445X 1879-1514 |
DOI: | 10.1016/j.aquatox.2004.07.005 |