Previously, the distribution of ammonia between the intracellular and extracellular compartments has been used to predict a significant depolarisation of the resting membrane potential (E(M)) of white muscle from brown trout (Salmo trutta) exposed to a sub-lethal combination of copper and low pH. However, this prediction is based upon two assumptions (i) a relatively high membrane permeability for the ammonium ion with respect to that for ammonia gas and (ii) that this is unaltered by exposure to copper and low pH. Since there is conflicting evidence in the literature of the validity of these assumptions, in the present study E(M) was directly measured in white muscle fibres of trout exposed to copper and low pH (E(M)=−52.2+/−4.9 mV) and compared with that of unexposed, control animals (E(M)=−86.5+/−2.9 mV) (means +/− s.e.m., N=6). In confirming the predicted depolarisation, these data support the hypothesis of electrophysiological impairment as a factor in the reduction in the swimming performance of trout exposed to these pollutants. In addition, the results of this study support the role of a significant permeability of the muscle membrane to NH(4)(+) in determining the distribution of ammonia in fish.

Bangsbo
J.
,
Kiens
B.
,
Richter
E. A.
(
1996
).
Ammonia uptake in inactive muscles during exercise in humans
.
Am. J. Physiol
270
,
101
–.
Beaumont
M. W.
,
Butler
P. J.
,
Taylor
E. W.
(
1995
).
Exposure of brown trout, Salmo trutta, to sub-lethal copper concentrations in soft acidic water and its effect upon sustained swimming performance
.
Aquat. Toxicol
33
,
45
–.
Beaumont
M. W.
,
Butler
P. J.
,
Taylor
E. W.
(
1995
).
Plasma ammonia concentration in brown trout (Salmo trutta) exposed to sub-lethal copper concentrations and its relationship to decreased swimming performance
.
J. Exp. Biol
198
,
2213
–.
Binstock
L.
,
Lecar
H.
(
1969
).
Ammonium ion currents in the squid giant axon
.
J. Gen. Physiol
53
,
342
–.
Butler
P. J.
,
Day
N.
,
Namba
K.
(
1992
).
Interactive effects of seasonal temperature and low pH on resting oxygen uptake and swimming performance of adult brown trout (Salmo trutta)
.
J. Exp. Biol
165
,
195
–.
Day
N.
,
Butler
P. J.
(
1996
).
Environmental acidity and white muscle recruitment during swimming in the brown trout (Salmo trutta)
.
J. Exp. Biol
199
,
1947
–.
Eugene
D.
,
Barets
A.
(
1983
).
Electrical activity of trout skeletal muscle fibers
.
J. Physiol., Paris
78
,
814
–.
Fraser
D. I.
,
Dyer
W. J.
,
Weinstein
H. M.
,
Dingle
J. R.
,
Hines
J. A.
(
1966
).
Glycolytic metabolites and their distribution at death in the white and red muscle of cod following various degrees of antemortem muscular activity
.
Can. J. Biochem
44
,
1015
–.
Grosell
M.
,
Boetius
I.
,
Hansen
H. J. M.
,
Rosenkilde
P.
(
1996
).
Influence of preexposure to sublethal levels of copper on64Cu uptake and distribution among tissues of the European eel (Anguilla anguilla)
.
Comp. Biochem. Physiol
114
,
229
–.
Grosell
M. H.
,
Hogstrand
C.
,
Wood
C. M.
(
1998
).
Renal Cu and Na excretion and hepatic Cu metabolism in both Cu acclimated and non acclimated rainbow trout (Oncorhynchus mykiss)
.
Aquat. Toxicol
40
,
275
–.
Heald
D. E.
(
1975
).
Influence of ammonium ions on mechanical and electrophysiological responses of skeletal muscle
.
Am. J. Physiol
229
,
1174
–.
Jenerick
H. P.
(
1959
).
The control of membrane ionic currents by the membrane potential of muscle
.
J. Gen. Physiol
42
,
923
–.
MacLean
D. A.
,
Barclay
J. K.
,
Graham
T. E.
(
1995
).
Electrical stimulation and amino acid and ammonia metabolism in the canine gastrocnemius muscle
.
Am. J. Physiol
268
,
759
–.
Marcaida
G.
,
Felipo
V.
,
Hermenegildo
C.
,
Miñana
M.-D.
,
Grisolía
S.
(
1992
).
Acute ammonia toxicity is mediated by the NMDA type of glutamate receptors
.
FEBS Lett
296
,
67
–.
Meyer
R. A.
,
Dudley
G. A.
,
Terjung
R. L.
(
1980
).
Ammonia and IMP in different skeletal muscle fibres after exercise in rats
.
J. Appl. Physiol
49
,
1037
–.
Milne
M. D.
,
Scribner
B. H.
,
Crawford
M. A.
(
1958
).
Non-ionic diffusion and the excretion of weak acids and bases
.
Am. J. Med
24
,
709
–.
Mommsen
T. P.
,
Hochachka
P. W.
(
1988
).
The purine nucleotide cycle as two temporally separated metabolic units: a study on trout muscle
.
Metabolism
37
,
552
–.
Pörtner
H. O.
,
Boutilier
R. G.
,
Tang
Y.
,
Toews
D. P.
(
1990
).
Determination of intracellular pH and P COafter metabolic inhibition by fluoride and nitrilotriacetic acid
.
Respir. Physiol
81
,
255
–.
Randall
D. J.
,
Brauner
C.
(
1991
).
Effects of environmental factors on exercise in fish
.
J. Exp. Biol
160
,
113
–.
Roos
A.
,
Boron
W. F.
(
1981
).
Intracellular pH
.
Physiol. Rev
61
,
296
–.
Rothman
S. M.
,
Olney
J. W.
(
1987
).
Excitotoxicity and the NMDA receptor
.
Trends Neurosci
10
,
299
–.
Saha
N.
,
Ratha
B. K.
(
1989
).
Comparative study of ureogenesis in freshwater, air-breathing teleosts
.
J. Exp. Zool
252
,
1
–.
Stabenau
J. R.
,
Warren
K. S.
,
Rall
D. P.
(
1959
).
The role of pH gradient in the distribution of ammonia between blood and cerebrospinal fluid
.
J. Clin. Invest
38
,
373
–.
Tang
Y.
,
Lin
H.
,
Randall
D. J.
(
1992
).
Compartmental2236distributions of carbon dioxide and ammonia in rainbow trout at rest and following exercise and the effect of bicarbonate infusion
.
J. Exp. Biol
169
,
235
–.
Wang
Y. X.
,
Heigenhauser
G. J. F.
,
Wood
C. M.
(
1994
).
Integrated responses to exhaustive exercise and recovery in rainbow trout white muscle: acid—base, phosphogen, carbohydrate, lipid, ammonia, fluid volume and electrolyte metabolism
.
J. Exp. Biol
195
,
227
–.
Wang
Y. X.
,
Heigenhauser
G. J. F.
,
Wood
C. M.
(
1996
).
Ammonia movement and distribution after exercise across white muscle cell membranes in rainbow trout
.
Am. J. Physiol
40
,
738
–.
Wendelaar Bonga
S. E.
(
1997
).
The stress response in fish
.
Physiol. Rev
77
,
591
–.
Wood
C. M.
,
Munger
R. S.
,
Toews
D. P.
(
1989
).
Ammonia, urea and H+distribution and the evolution of ureotelism in amphibians
.
J. Exp. Biol
144
,
215
–.
Wright
P. A.
,
Randall
D. J.
,
Wood
C. M.
(
1988
).
The distribution of ammonia and H+between tissue compartments in lemon sole (Parophrys vetulus) at rest, during hypercapnia and following exercise
.
J. Exp. Biol
136
,
149
–.
Wright
P. A.
,
Wood
C. M.
,
Randall
D. J.
(
1988
).
An in vitro and in vivo study of the distribution of ammonia between plasma and red cells of rainbow trout (Salmo gairdneri)
.
J. Exp. Biol
134
,
423
–.
This content is only available via PDF.