The effect of cortisol on Na(+)/K(+)-ATPase expression in the gill chloride cells of tilapia Oreochromis mossambicus was studied by immunocytochemistry at the light and electron microscope levels. One of three doses of cortisol (low, 125 mg kg(−1)food; middle, 375 mg kg(−1)food; high, 750 mg kg(−1) food) was administered via the food (at a ration of 1.5 % of body mass) and the fish were sampled after 5 days. Plasma osmolality and Na(+) levels were elevated in the middle- and high-dose groups, and plasma cortisol levels in the high-dose groups. Hematocrit values were not affected by the treatments. Opercular membrane chloride cell density increased by 94 % and 286 % in the middle- and high-dose fish, respectively, whereas the gill chloride cell frequency increased by up to 28 % maximally in the high-dose fish. Lamellar gill chloride cells were absent in the control and low-dose groups, but were observed in the middle- and high-dose groups. Cortisol increased the volume of the tubular membrane system in mature gill chloride cells. Quantification of immunogold-labelled Na(+)/K(+)-ATPase antigen (a 104 kDa protein species, as demonstrated by western blot) revealed that the high dose of cortisol increases the Na(+)/K(+)-ATPase density in the tubular system of chloride cells. This is the first direct evidence that cortisol not only increases chloride cell numbers but also Na(+)/K(+)-ATPase density in these cells.

Dang
Z. C.
,
Lock
R. A. C.
,
Flik
G.
,
Wendelaar Bonga
S. E.
(
2000
).
Na+/K+-ATPase immunoreactivity in branchial chloride cells of Oreochromis mossambicus exposed to copper
.
J. Exp. Biol
203
,
379
–.
Dange
A. D.
(
1986
).
Branchial Na+/K+-ATPase activity in freshwater or saltwater acclimated tilapia Oreochromis (Sarotherodon) mossambicus: effect of cortisol and thyroxine
.
Gen. Comp. Endocrinol
62
,
341
–.
Flik
G.
,
Perry
S. F.
(
1989
).
Cortisol stimulates whole-body calcium uptake and the branchial calcium pump in freshwater rainbow trout
.
J. Endocrinol
120
,
75
–.
Flik
G.
,
Van Rijs
J. H.
,
Wendelaar Bonga
S. E.
(
1985
).
Evidence for high affinity Ca2+-ATPase activity and ATP-driven Ca2+-transport in membrane preparations of the gill epithelium of the cichlid fish Oreochromis mossambicus
.
J. Exp. Biol
119
,
335
–.
Iger
Y.
,
Balm
P. H. M.
,
Jenner
H. A.
,
Wendelaar Bonga
S. E.
(
1995
).
Cortisol induces stress-related changes in the skin of rainbow trout (Oncorhynchus mykiss)
.
Gen. Comp. Endocrinol
97
,
188
–.
Li
J.
,
Eygensteyn
J.
,
Lock
R. A. C.
,
Wendelaar Bonga
S. E.
,
Flik
G.
(
1997
).
Na and Ca homeostatic mechanisms in isolated chloride cells of the teleost Oreochromis mossambicus analysed by confocal laser scanning microscopy
.
J. Exp. Biol
200
,
1499
–.
Mayer-Gostan
N.
,
Kosmann
H.
,
Watrin
A.
,
Payan
P.
,
Boeuf
G.
(
1997
).
Distribution of ionocytes in the saccular epithelium of the inner ear of two teleosts (Oncorhyncus mykiss and Scophthalamus maximus)
.
Cell Tissue Res
289
,
53
–.
McCormick
S. D.
(
1990
).
Cortisol directly stimulates differentiation of chloride cells in tilapia opercular membrane
.
Am. J. Physiol
259
,
857
–.
McCormick
S. D.
(
1996
).
Effects of growth hormone and insulin-like factor I on salinity tolerance and gill Na+/K+-ATPase in Atlantic salmon (Salmo salar): interaction with cortisol
.
Gen. Comp. Endocrinol
101
,
3
–.
McCormick
S. D.
,
Dickhoff
W. W.
,
Duston
J.
,
Nishioka
R. S.
,
Bern
H. A.
(
1991
).
Developmental differences in the responsiveness of gill Na+/K+-ATPase to cortisol in salmonids
.
Gen. Comp. Endocrinol
84
,
308
–.
Perry
S. F.
(
1997
).
The chloride cell: structure and function in the gills of freshwater fishes
.
Annu. Rev. Physiol
59
,
325
–.
Perry
S. F.
,
Laurent
P.
(
1989
).
Adaptational responses of rainbow trout to lowered external NaCl concentration: contribution of the branchial chloride cell
.
J. Exp. Biol
147
,
147
–.
Richman
N. H.
,
Zaugg
W.
(
1987
).
Effects of cortisol and growth hormone on osmoregulation in pre-and desmoltified coho salmon (Oncorhynchus kisutch)
.
Gen. Comp. Endocrinol
65
,
189
–.
Schreiber
A. M.
,
Specker
J. L.
(
1999
).
Metamorphosis in the summer flounder Paralichthys dentatus: changes in gill mitochondria-rich cells
.
J. Exp. Biol
202
,
2475
–.
Seidelin
M.
,
Madsen
S. S.
,
Byrialsen
A.
,
Kristiansen
K.
(
1999
).
Effects of insulin-like growth factor-I and cortisol on Na+/K+-ATPase expression in osmoregulatory tissues of brown trout (Salmo trutta)
.
Gen. Comp. Endocrinol
113
,
331
–.
Van der Heijden
A. J. H.
,
Verbost
P. M.
,
Eygensteyn
J.
,
Wendelaar Bonga
S. E.
,
Flik
G.
(
1997
).
Mitochondria-rich cells in gills of tilapia (Oreochromis mossambicus) adapted to freshwater or seawater: quantification by confocal laser scanning microscopy
.
J. Exp. Biol
200
,
55
–.
Wendelaar Bonga
S. E.
,
Flik
G.
,
Balm
P. H. M.
,
Van Der Meij
J. C. A.
(
1990
).
The ultrastructure of chloride cells in the gills of the teleost Oreochromis mossambicus during exposure to acidified water
.
Cell. Tissue Res
259
,
575
–.
Weyts
F. A. A.
,
Verburg-van Kemenade
B. M. L.
,
Flik
G.
(
1998
).
Characterisation of glucocorticoid receptors in peripheral blood leucocytes of carp, Cyprinus carpio L
.
Gen. Comp. Endocrinol
111
,
1
–.
Weyts
F. A. A.
,
Verburg-van Kemenade
B. M. L.
,
Flik
G.
,
Lambert
J. G. D.
,
Wendelaar Bonga
S. E.
(
1997
).
Conservation of apoptosis as an immune regulatory mechanism: effects of cortisol and cortisone on carp lymphocytes
.
Brain, Behav. Immun
11
,
95
–.
Witters
H.
,
Berckman
P.
,
Vangenechten
C.
(
1996
).
Immunolocalization of Na+/K+-ATPase in the gill epithelium of rainbow trout, Oncorhynchus mykiss
.
Cell. Tissue Res
283
,
461
–.
This content is only available via PDF.