title: Increased oxidative metabolism and myoglobin expression in zebrafish muscle during chronic hypoxia.
abstract: Fish may be extremely hypoxia resistant. We investigated how muscle fibre size and oxidative capacity in zebrafish (Danio rerio) adapt during severe chronic hypoxia. Zebrafish were kept for either 3 or 6 weeks under chronic constant hypoxia (CCH) (10% air/90%N2 saturated water). We analyzed cross-sectional area (CSA), succinate dehydrogenase (SDH) activity, capillarization, myonuclear density, myoglobin (Mb) concentration and Mb mRNA expression of high and low oxidative muscle fibres. After 3 weeks of CCH, CSA, SDH activity, Mb concentration, capillary and myonuclear density of both muscle fibre types were similar as under normoxia. In contrast, staining intensity for Mb mRNA of hypoxic high oxidative muscle fibres was 94% higher than that of normoxic controls (P<0.001). Between 3 and 6 weeks of CCH, CSA of high and low oxidative muscle fibres increased by 25 and 30%, respectively. This was similar to normoxic controls. Capillary and myonuclear density were not changed by CCH. However, in high oxidative muscle fibres of fish maintained under CCH, SDH activity, Mb concentration as well as Mb mRNA content were higher by 86%, 138% and 90%, respectively, than in muscle fibres of fish kept under normoxia (P<0.001). In low oxidative muscle fibres, SDH activity, Mb and Mb mRNA content were not significantly changed. Under normoxia, the calculated interstitial oxygen tension required to prevent anoxic cores in muscle fibres (PO2crit) of high oxidative muscle fibres was between 1.0 and 1.7 mmHg. These values were similar at 3 and 6 weeks CCH. We conclude that high oxidative skeletal muscle fibres of zebrafish continue to grow and increase oxidative capacity during CCH. Oxygen supply to mitochondria in these fibres may be facilitated by an increased Mb concentration, which is regulated by an increase in Mb mRNA content per myonucleus.
authors: Laboratory for Myology, MOVE Research Institute Amsterdam, Faculty of Human Movement Sciences, VU University Amsterdam, 1081 BT Amsterdam, The Netherlands r.t.jaspers@vu.nl.
authors: Richard T
authors: RT
authors: Jaspers
authors: Laboratory for Myology, MOVE Research Institute Amsterdam, Faculty of Human Movement Sciences, VU University Amsterdam, 1081 BT Amsterdam, The Netherlands Department of Integrative Zoology, Institute of Biology, Leiden University, 2333 BE Leiden, The Netherlands.
authors: Janwillem
authors: J
authors: Testerink
authors: UFR Biomédicale des Saints-Pères, CESEM, UMR 8194 CNRS, Paris, France.
authors: Bruno
authors: B
authors: Della Gaspera
authors: UFR Biomédicale des Saints-Pères, CESEM, UMR 8194 CNRS, Paris, France.
authors: Christophe
authors: C
authors: Chanoine
authors: Department of Molecular Genetics, Prenatal Medicine Munich, 80639 Munich, Germany.
authors: Christophe P
authors: CP
authors: Bagowski
authors: Department of Physiology, Institute for Cardiovascular Research, VU University Medical Center, 1007 MB Amsterdam, The Netherlands.
authors: Willem J
authors: WJ
authors: van der Laarse
keywords: Acclimation; Acclimatization; Adaptation; Capillarization; Chronic hypoxia; Critical oxygen tension; Endurance; Hypertrophy; Mitochondrial density; Myoglobin; Skeletal muscle