Tolerance of hypercapnic acidosis by the European eel, Anguilla anguilla

TY - ABST

T1 - Tolerance of hypercapnic acidosis by the European eel, Anguilla anguilla

AU - McKenzie, DJ

AU - Dalla Valle, AZ

AU - Steffensen, JF

AU - Taylor, EW

N1 - Udgivelsesdato: February 2000 Volumne: 523

PY - 2000

Y1 - 2000

N2 - Eels reared intensively in recirculated water can experience chronic hypercapnia from accumulation of metabolic CO2, with water CO2 partial pressures (Pw,CO2) exceeding 30 mmHg, far above that hitherto considered normal for fish (1 to 3 mmHg). The effects on eels of acute and chronic hypercapnia were investigated. Eels (n = 6) were anaesthetised (0.05 % MS-222 in water), cannulated in the dorsal aorta for withdrawal of blood samples and in the operculum for measurement of gill ventilation rate (fG) and pressure amplitude (POP). A flow cuff placed on the ventral aorta measured cardiac output (CO). Eels were recovered for 48 h in respirometer chambers provided with a flow of normocapnic water. Instantaneous O2 uptake was measured every 10 min with an automated system. All data are reported as means ± S.E.M., means compared by ANOVA, significance attributed at P < 0.05. Acute exposure to progressive hypercapnia (20 min at Pw,CO2 values of 10, 20, 40, 60 and 80 mmHg) caused a linear increase in arterial PCO2 (Pa,CO2) from 3.5 ± 0.4 mmHg in normocapnia to 44.9 ± 2.6 at Pw,CO2 = 80 mmHg, coupled to respective declines in arterial pH (pHa) from 7.86 ± 0.02 to 7.16 ± 0.04 and in arterial total O2 content (ca,O2) from 9.6 ± 0.7 to 2.0 ± 0.5 vol%. There was a significant increase in fG and POP at Pw,CO2 values of 10, 20, 40 mmHg, then a decline in fG but further increase in POP at Pw,CO2 = 60 and 80 mmHg. Despite the severe acidosis and hypoxaemia, there were no significant effects on CO or O2 uptake. Eels exposed for 3 months to chronic hypercapnia (Pw,CO2 values of control, 15, 30 or 45 mmHg) were anaesthetised, cannulated and recovered as described above, at the appropriate Pw,CO2. In all groups, Pa,CO2 was about 3 mmHg above Pw,CO2, and hypercapnic eels exhibited a marked accumulation of plasma bicarbonate, from 12.8 ± 1.5 mmol l-1 in controls (n = 6) to 72.5 ± 4.1 at Pw,CO2 = 45 mmHg (n = 4). The bicarbonate accumulation buffered the effects of hypercapnia on pHa and ca,O2, as compared with the acute exposure. Nonetheless, in the eels at Pw,CO2 = 45 mmHg, pHa was 7.57 ± 0.04 and ca,O2 5.5 ± 2.2 vol%, significantly lower than in the control animals, where pHa was 7.89 ± 0.04 and ca,O2 11.6 ± 1.5 vol%. Exercise performance was studied in a swimming respirometer. Stepwise increases in swimming speed caused similar, exponential increases in O2 uptake in all groups, with no differences in tailbeat frequencies, aerobic scope or maximum sustainable swimming speed. The results indicate that the eel is extremely tolerant of hypercapnic acidosis. Acute, severe acidosis and hypoxaemia had no effect on CO or whole animal O2 uptake; chronic acidosis and hypoxaemia had no effect on the ability to increase O2 uptake and perform muscular work during exercise.

AB - Eels reared intensively in recirculated water can experience chronic hypercapnia from accumulation of metabolic CO2, with water CO2 partial pressures (Pw,CO2) exceeding 30 mmHg, far above that hitherto considered normal for fish (1 to 3 mmHg). The effects on eels of acute and chronic hypercapnia were investigated. Eels (n = 6) were anaesthetised (0.05 % MS-222 in water), cannulated in the dorsal aorta for withdrawal of blood samples and in the operculum for measurement of gill ventilation rate (fG) and pressure amplitude (POP). A flow cuff placed on the ventral aorta measured cardiac output (CO). Eels were recovered for 48 h in respirometer chambers provided with a flow of normocapnic water. Instantaneous O2 uptake was measured every 10 min with an automated system. All data are reported as means ± S.E.M., means compared by ANOVA, significance attributed at P < 0.05. Acute exposure to progressive hypercapnia (20 min at Pw,CO2 values of 10, 20, 40, 60 and 80 mmHg) caused a linear increase in arterial PCO2 (Pa,CO2) from 3.5 ± 0.4 mmHg in normocapnia to 44.9 ± 2.6 at Pw,CO2 = 80 mmHg, coupled to respective declines in arterial pH (pHa) from 7.86 ± 0.02 to 7.16 ± 0.04 and in arterial total O2 content (ca,O2) from 9.6 ± 0.7 to 2.0 ± 0.5 vol%. There was a significant increase in fG and POP at Pw,CO2 values of 10, 20, 40 mmHg, then a decline in fG but further increase in POP at Pw,CO2 = 60 and 80 mmHg. Despite the severe acidosis and hypoxaemia, there were no significant effects on CO or O2 uptake. Eels exposed for 3 months to chronic hypercapnia (Pw,CO2 values of control, 15, 30 or 45 mmHg) were anaesthetised, cannulated and recovered as described above, at the appropriate Pw,CO2. In all groups, Pa,CO2 was about 3 mmHg above Pw,CO2, and hypercapnic eels exhibited a marked accumulation of plasma bicarbonate, from 12.8 ± 1.5 mmol l-1 in controls (n = 6) to 72.5 ± 4.1 at Pw,CO2 = 45 mmHg (n = 4). The bicarbonate accumulation buffered the effects of hypercapnia on pHa and ca,O2, as compared with the acute exposure. Nonetheless, in the eels at Pw,CO2 = 45 mmHg, pHa was 7.57 ± 0.04 and ca,O2 5.5 ± 2.2 vol%, significantly lower than in the control animals, where pHa was 7.89 ± 0.04 and ca,O2 11.6 ± 1.5 vol%. Exercise performance was studied in a swimming respirometer. Stepwise increases in swimming speed caused similar, exponential increases in O2 uptake in all groups, with no differences in tailbeat frequencies, aerobic scope or maximum sustainable swimming speed. The results indicate that the eel is extremely tolerant of hypercapnic acidosis. Acute, severe acidosis and hypoxaemia had no effect on CO or whole animal O2 uptake; chronic acidosis and hypoxaemia had no effect on the ability to increase O2 uptake and perform muscular work during exercise.

M3 - Conference abstract in journal

SN - 0022-3751

SP - 282P-283P

JO - The Journal of Physiology

JF - The Journal of Physiology

IS - Suppl. S

T2 - Tolerance of hypercapnic acidosis by the European eel, Anguilla anguilla

Y2 - 29 November 2010

ER -