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Cardiorespiratory adjustments during hypercarbia in rainbow trout Oncorhynchus mykiss are initiated by external CO2 receptors on the first gill arch

Steve F. Perry* and Stephen G. Reid

Department of Biology, University of Ottawa, 50 Marie Curie, Ottawa, Ontario, Canada, K1N 6N5



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  		Fig. 1. The effects of acute hypercarbia (indicated by the shaded areas) on (A) water PCO2 (PWCO2), (B) cardiac frequency (fH), (C) arterial blood pressure (Pa) and (D) systemic vascular resistance (RS) in rainbow trout (Oncorhynchus mykiss) previously subjected to sham extirpation (controls; open circles; N=16) or bilateral extirpation (filled symbols; N=12) of the first gill arch. Values are means ± 1 S.E.M.; significant differences (P<0.05) from pre-hypercarbic values (time=0) are denoted by horizontal lines, whereas significant differences (P<0.05) between control and extirpated fish are indicated by daggers. 1 mmHg=0.133 kPa.

 


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  		Fig. 2. (A-C) The effects of acute hypercarbia (indicated by the shaded areas) on (A) water PCO2 (PWCO2; same data as Fig. 1A), (B) ventilation amplitude (VAMP) and (C) ventilation frequency (fG) in rainbow trout Oncorhynchus mykiss previously subjected to sham extirpation (controls; open circles; N=16) or bilateral extirpation (filled symbols; N=12) of the first gill arch. Values are means ± 1 S.E.M.; significant differences (P<0.05) from pre-hypercarbic values (time=0) are denoted by horizontal lines, whereas significant differences (P<0.05) between control and extirpated fish are indicated by daggers. (D) Relationships between water PCO2 (PWCO2) and VAMP in intact (open circles; r2=0.97) and gill-extirpated (filled circles; r2=0.84) rainbow trout. The data represent mean values for 2 min intervals immediately prior to, and during, the 20 min period of hypercarbia. The non-linear regression (double rectangular four-parameter hyperbola) for the intact fish was generated using iterative curve-fitting software (Sigmaplot 2001; SPSS Inc.). 1 mmHg=0.133 kPa.

 


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  		Fig. 3. (A) The effects of acute hypercarbia (indicated by the shaded area) on cardiac frequency (fH) in control (open circles; N=16) and atropinised (shaded symbols; N=7) rainbow trout (Oncorhynchus mykiss). The data are presented as means ± 1 S.E.M.; significant differences (P<0.05) from pre-hypercarbic values (time=0) are denoted by a horizontal line. (B) Relationships between water PCO2 (PwCO2) and fH in intact (open circles; r2=0.97), atropinised (shaded circles; r2=0.75) and gill-extirpated (filled circles; r2=0.90) rainbow trout. The data represent mean values for 2 min intervals immediately prior to, and during, the 20 min period of hypercarbia. The non-linear regression (four-parameter exponential decay) for the intact fish was generated using iterative curve-fitting software (Sigmaplot 2001; SPSS Inc.). 1 mmHg=0.133 kPa.

 


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  		Fig. 4. The effects of a bolus injection of CO2-enriched water (5% CO2) into the buccal cavity on (A) cardiac frequency (fH), (B) arterial blood pressure (Pa), (C) ventilation amplitude (VAMP), (D) systemic vascular resistance (RS), (E) cardiac output (b) and (F) ventilation frequency (fG) in rainbow trout Oncorhynchus mykiss previously subjected to sham extirpation (controls; open circles; N=22) or bilateral extirpation (filled symbols; N=11) of the first gill arch. Values are means ± 1 S.E.M.; significant differences (P<0.05) from pre-injection values (time=0) are denoted by asterisks, whereas significant differences (P<0.05) between control and extirpated fish are indicated by daggers. 1 mmHg=0.133 kPa.

 


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  		Fig. 5. The effects of a bolus injection of CO2-enriched saline (5% CO2; open circles; N=8) or air-equilibrated saline (controls; filled circles; N=8) into the caudal vein on (A) cardiac frequency (fH), (B) arterial blood pressure (Pa), (C) ventilation amplitude (VAMP), (D) systemic vascular resistance (RS), (E) cardiac output (Vb) and (F) ventilation frequency (fG) in intact rainbow trout (Oncorhynchus mykiss). Values are means ± 1 S.E.M.; significant differences (P<0.05) from pre-injection values (time=0) are denoted by asterisks. There were no significant differences between the control and treatment groups at any measurement time. 1 mmHg=0.133 kPa.

 

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© The Company of Biologists Ltd 2002