Fish muscle energy metabolism measured during hypoxia and recovery: an in vivo 31P-NMR study

Abstract

Three fish species were exposed to graded hypoxia levels and allowed to recover. Levels of high-energy phosphate compounds in epaxial white muscle were monitored by in vivo 31P nuclear magnetic resonance (NMR) spectroscopy. Furthermore, O2 consumption of the animals was measured. With increasing hypoxia load, metabolic parameters started to change in the following order: phosphocreatine (PCr)-to-Pi ratio (decrease), O2 consumption (decrease), [PCr] (decrease), intracellular pH (pHi; decrease), Pi (increase), free ADP concentration ([ADP]free; increase), [ATP] (decrease). PCr levels fell with the PO2. After each increment, the [PCr] reached a stable plateau value while, in some cases, a recovery was observed. This recovery could be explained because the balance between anaerobic and aerobic metabolism is continuously fluctuating during hypoxia as a consequence of changes in the activity of the fish. Consequently the [ADP]free are fluctuating, resulting in an activation of the creatine kinase reaction and the anaerobic glycolysis. In all three species, anaerobic glycolysis was activated, but in contrast to anoxia exposure, metabolic suppression was absent. The changes of [ADP]free and [H+] (which influences the position of the creatine kinase equilibrium) are species dependent. Species differences observed in the other parameters were small. It is concluded that the pattern of the activation of anaerobic metabolism under deep hypoxia is different from that under anoxia.

Differential recovery from exercise and hypoxia exposure measured using 31P- and 1H-NMR in white muscle of the common carpCyprinus carpio

“…Special care was taken to ensure that there was ~5 mm of clearance between the fish and the box to avoid compression and possible muscle ischemia. In our hands, the time taken for laterally oriented carp to rebuild PCr following hypoxia exposure are comparable with that observed by van den Thillart et al (van den Thillart et al, 1989) and van Ginneken et al (van Ginneken et al, 1995) where the probe design allowed the fish to recover in a vertical position. …”

“…P-NMR has been extensively used in fish during hypoxia exposure and recovery (Borger et al, 1998;van den Thillart et al, 1989;van Ginneken et al, 1995;Van Waarde et al, 1990), but 1 H-NMR has been used in only a few studies (Bock et al, 2002;Wasser et al, 1992a;Yoshizaki et al, 1981) and has not been extensively used in fish to examine metabolic recovery from exercise or hypoxia.…”

AMP-activated protein kinase activity during metabolic rate depression in the hypoxic goldfish,Carassius auratus

“…The maintenance of high muscle [ATP] during hypoxia exposure, as seen in other studies (Fig. 5A) (Richards et al, 2007;van Ginneken et al, 1995;Zhou et al, 2000), may impede AMPK activation since, as mentioned previously, ATP competitively inhibits AMP binding to AMPK. Table 4), suggesting that only at >12 h hypoxia exposure might goldfish muscle experience an energy stress great enough to result in the activation of AMPK and the need to activate biochemical means of reducing ATP demands.…”

Temperature-dependent pH regulation in eurythermal and stenothermal marine fish: an interspecies comparison using 31P-NMR

“…Although the possibility for the fish to move inside the chambers could lead to movement artefacts, spectral quality and time resolution were comparable to investigations where the animal was either anaesthetized and/ or vertically fixed (Van den Thillart et al, 1989a, b;Van Ginneken et al, 1995, Borger et al, 1998Moerland and Eggington, 1998). The potential influence of anaesthetics on blood, tissue and acid-base parameters as reported for rainbow trout (Iwama et al 1989) and in the Antarctic fish Pagothenia borchgrevinki (Ryan 1992) could be excluded.…”