Ha. Campbell et al., Copper uptake kinetics across the gills of rainbow trout (Oncorhynchus mykiss) measured using an improved isolated perfused head technique, AQUAT TOX, 46(3-4), 1999, pp. 177-190
Measurements of branchial Cu uptake in vivo are complicated by rapid change
s in the Cu stores of other body compartments such as the blood and liver.
This study eliminates these problems by adopting an in vitro approach. The
perfused head technique was improved and viability extended to 2 h or more;
so that kinetic studies on CLI uptake could be performed. The improvements
included the use of Leibovitz L-15 culture medium instead of saline perfus
ates, ventilation of the gills with single pass flowing water to allow cont
rol of metal speciation, and the use of surgical glue rather than sutures t
o greatly reduce surgery time. Viability was assessed by perfusion pressure
of < 50 cm H2O, demonstration of net Na influx, < 7.1 IU ml(-1) of lactate
dehydrogenase (LDH) activity in the perfusate, and a steady-state ethanol
permeability of the gills to indicate the;absence of changes in functional
gill area. Gill morphology was also checked histologically. Concentrations
of Cu > 10 mu mol l(-1) caused only slight effects on some secondary lamell
ae, but this did not effect gill haemodynamics, gill permeability (ethanol
uptake), or perfusate LDH activity when compared to similar measurements in
non-viable preparations. Cumulative Cu uptake into the perfusate did not f
ollow changes in perfusate flow and reached a steady state in about 1 h. Co
pper uptake kinetics based on the total Ca concentration in the water fitte
d a rectangular hyperbole (the Michaelis equation) with a regression coeffi
cient (r(2)) of 0.98. The K-m and V-max values were 11.85 +/- 2.8 mu mol l(
-1) and 52.2 +/- 4.9 nmol kg(-1) h(-1), respectively (mean +/- SE, n = 5).
Copper uptake rate plotted against free divalent Cu (Cu2+) in the water did
not fit the Michaelis equation, but showed second order reaction kinetics
(r(2) = 0.87) with a rate Constant (k) of 4.43. Copper uptake was abolished
by the serosal application of 50 mu mol l(-1) vanadate. These observations
suggest that Cu uptake by the gills is mediated through a vanadate sensiti
ve P-type ATPase which has a similar K-m (total Cu) to the mammalian Cu-ATP
ase. The second order reaction kinetics for Cu2+ uptake from the water is c
onsistent with the reduction of Cu2+ to Cu+ prior to membrane transport, as
observed in mammalian cells. (C) 1999 Elsevier Science B.V. All rights res
erved.