230
PL.M. van Dijk et al.
synthesis. Therefore, lower ADP/O values may be expected in cold
adapted animals when acutely exposed to warmer temperatures. We
suggest that an increase of aerobic capacity in Antarctic fish tissues
brought about by an increase of the number of mitochondria in
combination with homeoviscous adaptation of mitochondrial membranes
may set the upper temperature limit at which oxidative phosphorylation
can work efficiently [37]. The low tolerance of Antarctic animals towards
temperature elevation may be due to increased proton leakiness of the
inner mitochondrial membranes at higher temperatures.
Anaerobic Capacity
During burst swimming total ATP turnover may increase over 100-fold
compared to resting rates [12]. Oxidative metabolism alone is not able to
meet these high rates of energy utilization. In fast twitch white muscles
anaerobic glycolysis is the major source of energy during burst swimming
in fish. High glycolytic rates lead to an accumulation of lactate and
protons in the muscle tissue.
Rainbow trout acclimated to 5 °C or 18°C accumulated the same
amounts of lactate in the white muscle during exhaustive swimming [38].
These results are in contrast to data on roach [39,40] in which a change of
acclimation from 20 °C to 4 °C leads to 50% reduction of lactate
formation during exhaustive exercise. Data on changes of glycolytic
enzyme activities are also contradictory. While trout and lake whitefish
(Coregonus clupeaformis) show a compensatory increase of hexokinase
and phosphofructokinase activities during cold acclimation [30,31], these
enzymes are even less active in cold acclimated goldfish and striped bass
[27,41]. Guderley [23] suggested that glycolytic enzymes may increase in
species which do not change mitochondrial enzyme activity during cold
acclimation (as in salmonids), while they may tend to decrease in species
which exhibit a compensatory rise in oxidative enzyme activity.
A number of studies on capture and exercise stress in Antarctic
notothenioids suggest that the anaerobic capacity of these animals is
greatly reduced [42]. Exhaustive exercise induced only a minor increase
of lactate in the white muscle of about 1-3 !lmol g-l in N coriiceps and P.
borchgrevinki [9,43]. Dunn and Johnston [43] examined maximal
activities of glycolytic enzymes in N coriiceps and concluded that the
absence of lactate production is caused by a reduced glycolytic capacity in
these fish. Enzyme profiles for several notothenioids show the same trend:
generally, oxidative enzymes and creatine kinase show high degrees of
cold compensation, while glycolytic enzymes do not [19,33]. The reduced
PL.M. van Dijk et al.
synthesis. Therefore, lower ADP/O values may be expected in cold
adapted animals when acutely exposed to warmer temperatures. We
suggest that an increase of aerobic capacity in Antarctic fish tissues
brought about by an increase of the number of mitochondria in
combination with homeoviscous adaptation of mitochondrial membranes
may set the upper temperature limit at which oxidative phosphorylation
can work efficiently [37]. The low tolerance of Antarctic animals towards
temperature elevation may be due to increased proton leakiness of the
inner mitochondrial membranes at higher temperatures.
Anaerobic Capacity
During burst swimming total ATP turnover may increase over 100-fold
compared to resting rates [12]. Oxidative metabolism alone is not able to
meet these high rates of energy utilization. In fast twitch white muscles
anaerobic glycolysis is the major source of energy during burst swimming
in fish. High glycolytic rates lead to an accumulation of lactate and
protons in the muscle tissue.
Rainbow trout acclimated to 5 °C or 18°C accumulated the same
amounts of lactate in the white muscle during exhaustive swimming [38].
These results are in contrast to data on roach [39,40] in which a change of
acclimation from 20 °C to 4 °C leads to 50% reduction of lactate
formation during exhaustive exercise. Data on changes of glycolytic
enzyme activities are also contradictory. While trout and lake whitefish
(Coregonus clupeaformis) show a compensatory increase of hexokinase
and phosphofructokinase activities during cold acclimation [30,31], these
enzymes are even less active in cold acclimated goldfish and striped bass
[27,41]. Guderley [23] suggested that glycolytic enzymes may increase in
species which do not change mitochondrial enzyme activity during cold
acclimation (as in salmonids), while they may tend to decrease in species
which exhibit a compensatory rise in oxidative enzyme activity.
A number of studies on capture and exercise stress in Antarctic
notothenioids suggest that the anaerobic capacity of these animals is
greatly reduced [42]. Exhaustive exercise induced only a minor increase
of lactate in the white muscle of about 1-3 !lmol g-l in N coriiceps and P.
borchgrevinki [9,43]. Dunn and Johnston [43] examined maximal
activities of glycolytic enzymes in N coriiceps and concluded that the
absence of lactate production is caused by a reduced glycolytic capacity in
these fish. Enzyme profiles for several notothenioids show the same trend:
generally, oxidative enzymes and creatine kinase show high degrees of
cold compensation, while glycolytic enzymes do not [19,33]. The reduced