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First published online May 21, 2007
Journal of Experimental Biology 210, 1935-1943 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.005371

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Responses to hypoxia and recovery: repayment of oxygen debt is not associated with compensatory protein synthesis in the Amazonian cichlid, Astronotus ocellatus

J. M. Lewis^1,*, I. Costa¹, A. L. Val², V. M. F. Almeida-Val², A. K. Gamperl¹ and W. R. Driedzic¹

¹ Ocean Sciences Centre, Memorial University of Newfoundland, St. John's, NL, A1C 5S7, Canada
² Laboratory of Ecophysiology and Molecular Evolution, Instituto Nacional de Pesquisas da Amazônia, Alameda Cosme Ferreira, 1756, 69.083-000, Manaus, Amazonas, Brazil

View larger version (10K): [in this window] [in a new window]   Fig. 1. Routine metabolic rate (RoMR) in A. ocellatus in relation to changing levels of O2 saturation in the water. RoMR (O2) measurements are shown as means ± s.e.m., N=8 fish. *Significant differences in RoMR from time 0 (normoxia) values (P<0.05).

View larger version (8K): [in this window] [in a new window]   Fig. 2. Lactate concentration in plasma, brain, white muscle and liver tissue of A. ocellatus during normoxia, hypoxia and recovery from hypoxia. Values are means ± s.e.m.; numbers of samples/fish were: plasma normoxic (N=4), hypoxic (N=8), recovery (N=7); brain normoxic (N=6), hypoxic (N=10), recovery (N=20); muscle normoxic (N=12), hypoxic (N=12), recovery (N=20); liver normoxic (N=11), hypoxic (N=10), recovery (N=9). Significant differences within each tissue are indicated by different letters, P<0.05.

View larger version (11K): [in this window] [in a new window]   Fig. 3. Post-injection changes in the specific activity of the intracellular free phenylalanine pool in (A) liver, (B) brain, (C) heart, (D) gill and (E) white muscle of A. ocellatus during normoxia (closed circles) and hypoxia (open circles). Values are means ± s.e.m., N=4.

View larger version (11K): [in this window] [in a new window]   Fig. 4. Post-injection time course for the incorporation of radiolabelled phenylalanine into protein in A. ocellatus during normoxia (closed circles) and severe hypoxia (open circles). (A) Liver (y=0.47x+0.62, r2=0.60, Pr=0.05, Py=0.22; y=0.44x–0.22, r2=0.80, Pr=0.003, Py=0.39); (B) brain (y=0.82x–0.05, r2=0.92, Pr=2.35x10–5, Py=0.84; y=0.57x+0.07, r2=0.95, Pr=2.97x10–6, Py=0.61); (C) heart (y=0.94x+0.20, r2=0.80, Pr=0.005, Py=0.71; y=0.55x–0.16, r2=0.84, Pr=6.78x10–4, Py=0.53); (D) gill (y=2.34–0.24, r2=0.93, Pr=1.56x10–5, Py=0.72; y=1.05x+0.21, r2=0.68, Pr=0.015, Py=0.79). For each tissue regression equations refer to normoxic and hypoxic fish, respectively. All r2 values are significant (Pr<0.05), all y-intercept values are not significant from zero (Py>0.05). Values are means ± s.e.m., N=4, except for hypoxia-exposed liver 2 h sample, where N=3. White muscle not shown because rates of incorporation were not detectable.

View larger version (24K): [in this window] [in a new window]   Fig. 5. (A) Routine metabolic rate RoMR and (B–E) tissue phenylalanine incorporation in liver (A), brain (B), heart (C) and (D) gill, in A. ocellatus exposed to normoxia, severe hypoxia, and during recovery from hypoxia. Values are means ± s.e.m., N=8 for routine metabolic rate measurements. For phenylalanine incorporation measurements, N=12 for normoxia and hypoxia exposure, and N=4 for each time point during recovery. Different lowercase letters indicate a significant difference; P<0.05.