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Effects of simultaneous changes of water temperature and oxygenation on the acid-base balance of the shore crab, Carcinus maenas
Camp. Biochem. Physiol. Vol.
81A, No. 2, pp. 259-262, 1985
0300-9629/85$3.00+ 0.00 0 1985Pergamon Press Ltd
Printed in Great Britain
EFFECTS OF SIMULTANEOUS CHANGES OF WATER TEMPERATURE AND OXYGENATION ON THE ACID-BASE BALANCE OF THE SHORE CRAB, CARCINUS MAENAS P. DEJOURS*,A. TOULMOND~ and J.-P. TRUCHOT~ Station Biologique, Roscoff, France (Received 5 October 1984) Abstract-l. Shore crabs Curcinus maenas were exposed to constant normoxic Po, (isobaric normoxia) or constant normoxic Co, (isoconcentration normoxia), at ambient seawater temperature of 7, 16 and 25”C, and constant Pco,, 0.82 torr. The acid-base balance (ABB) of prebranchial hemolymph was assessed by measuring pH and P,!. 2. The pHi-temperature relationship was the same in isobaric and isoconcentration normoxia, but the temperature-dependent variations of fico2 were more marked in the second condition. This implies that the hemolymph carbonate concentration variations paralleled the P’Eco2changes. 3. By contrast, in the freshwater decapod crayfish Astacus leptodactylus, temperature-dependent changes of fiCO? and carbonate concentration are different in isobaric and isoconcentration normoxia. 4. In studies of respiration and ABB of water breathers, an essential prerequisite is an excellent regulation of ambient PO,, Pco,, ionic composition and temperature, because, as these experiments illustrate, the changes of ABB with ambient temperature variation are influenced by the effect of temperature on the ambient 0, concentration, which itself also contributes to the observed respiratory and ABB responses.
the saturating water vapor pressure with the increase of the temperature. The conclusion was that a decrease of hemolymph pH with a rise in temperature at constant PO, is partially offset by the concomitant decrease of water Co,. At constant PO,, the pH vs temperature slope was -0.008 pH unit .“C-‘; at constant CoZ the mean slope was -0.014 pH unit. “C- ’ . Here, we examine whether the marine decapod, the shore crab Carcinus maenas, behaves like the freshwater crayfish. The hemolymph ABB of shore crabs was measured as a function of temperature either at constant Pco,, or at constant Co,. The results in the crab are different from those in the crayfish, but they do show that the ABB variations with temperature are not the same in 0, isoconcentration normoxia and in isobaric normoxia.
INTRODUCTION For about twenty years the effects of variations
of the
ambient temperature on blood acid-base balance (ABB) have been intensively studied. Recent reviews include Rahn et ~2. (1975), Reeves (1977), Heisler (1981), Somero (1981) and Rahn and Howell (1978). The main results may be thus summarized: in poikilotherms, the blood pH decreases with an increase of temperature, an almost linear relation with an average slope of -0.017 pH unit.“C-‘. The slope of the neutral water pH vs temperature is nearly the same. Blood pH is always higher than water pH. But there are some exceptions among air and water breathers (see for references Dejours and Armand, 1983). These authors have sought to see, in the crayfish Astacus leptodactylus, if the changes of ABB with temperature could be entirely ascribed to thermal change, or if they were somewhat influenced by the effect of temperature variations in air-equilibrated water on the water O2 concentration. The O2 concentration could be affected for two reasons: (1) principally the decrease of O2 solubility with increase of temperature; (2) to a lesser extent, the decrease of the O2 partial pressure, PO,, in the gas phase (and thus in the air-equilibrated water) because of the increase of
MATERIALS AND METHODS Two series of experiments were conducted in the summer of 1983 at the Roscoff Biological Station in Brittany, France. We here report one series; the other gave nearly identical results. Control of the ambient conditions in the water bath
*Laboratoire de Physiologie Respiratoire, CNRS, 23 rue Becquerel, 67087 Strashourg, France. TBiologie et Physiologie des Organismes Marins, UniversitC Pierre-et-Marie-Curie, 4 place Jussieu, 75230 Paris 5, France. $.Station Marine, Laboratorie de Neurobiologie et Physiologie Comparkes, 2 rue du Professeur Jolyet, 33120 Arcachon, France.
We used a 55 liter rectangular tank, about 18 cm deep; the animals were prevented from surfacing since emersion entails respiratory acidosis (Truchot, 1975b). The tank water was renewed at a rate of about 0.2 I’min-’ and vigorously agitated by (1) an intense bubbling at various tank sites, (2) an external pump which recycled the water at a rate of 4 I’min-‘. The water was then satisfactorily homogenous, as demonstrated by temperature (and eventually P,, and pH) measurements at different tank sites. The seawater salinity was 35.06%0 and titration alkalinity 2.44 meq’l-‘. In this water three ambient factors were
259
260
P. DEJOURS et al.
regulated, namely temperature, Po, and pH (which implies a regulation of the whole carbonic system since TA was virtually constant). Temperature. The water was thermostatically controlled at 7, 16 or 25°C + 0.5”C. The source of cold or warm water was located outside the tank and fed a glass and rubber heat exchanger located in a side compartment of the tank. Oxygenation. Experiments were performed in one of the two conditions: (1) either Po, was maintained constant at a value of a few torrs above the actual ambient Paz which varies with the barometric pressure and the water vapor tension: arbitrarily the normoxic Po, was fixed at 158 torr; (2) or oxygen concentration, Co,, was maintained constant at the value prevailing at 16°C when the Po, value was 158 torr, namely 0.252 mmol.l-‘. For water temperatures at 7 and 25°C the chosen PO2 value took into account the 0, solubility decrease with the increase of temperature, namely Po, = 131.5 torr for 7°C and PO, = 183.9 torr at 25°C (Fig. 1). Thus we worked either at normoxic 0, tensions of 158 torr whatever the temperature (N’, Ni6, N2$ that is in isobaric normoxia, or at the normoxic oxygenation concentrations of 0.252mmol.l-’ (h7, Nn’, H”‘) which may be called isoconcentration normoxia (Fig. 1). PO, was fixed at the values of 158, 131.5 or 183.9 torr by means of an O,-stat which, by a system identical in principle to a pH-CO?-stat (Dejours and Armand, 1980) admits a proper amount of N, in order to fix water PO2 at 131.5 or admits O? to fix water PO2 at 183.9 torr. The PO, values were checked regularly during the experimental session and varied within a range of +3 torr. Acid-base balance. The water ABB was regulated by a pH-CO,-stat (Dejours and Armand, 1980) such that P,,, was about 0.82 torr. Seawater was equiiibrated at 7, 16 or 25°C with a CO,-containing mixture (about 0.82 torr), delivered by a Wiisthoff pump; the pH values of these waters, 7.72, 7.75 and 7.82, respectively, were then measured and used as set points of the pH-CO,-stat. The figures the water tank pH-CO,-stat displayed were arbitrary units chosen so that the actual pH measured with excellent reproducibility by a calibrated pH electrode was within +0.02 pH unit of the above values.
1. Duration for acclimation to new ambient conditions. Forty crabs kept in air-equilibrated seawater at 15-16°C were placed in an h’ water (Fig. 1) that is at 7°C with a Po?, P cOz and pH of about 131.5 torr, 0.82 torr and 7.82. The next day, after at least 16 hr of exposure to the h’ conditions, the hemolymph ABB of 12 crabs was determined. The same procedure was renewed after one and two days more of exposure. Thus there were three groups of 12 animals each exposed for at least 15, 40 or 60 hr, namely h:, hi and hi. As will be seen below, 16 hr was sufficient to reach a new ABB steady state. 2. The hemolymph acid-base balance in animals exposed to 7, 16 or 25°C in isobaric normoxia or in isoconcentration normoxie. Fifteen crabs were immersed in the late afternoon in a tank with the required temperature, pH (PcOJ and Po, of acclimation. These animals were studied after at least 40 hr of exposure, although 16 hr would have been enough. We measured hemolymph of 12 animals only; the extra animals constituted a reserve in case hemolymph samplings were defective.
Protocol
(2) The hemolymph
The experimental animals were kept in a large, wellaerated tank in which the seawater was continuously renewed at a temperature of 15-l 6°C. They were fed every day with fresh limpets.
Hemolymph acid-base balance measurements Hemolymph was sampled anaerobically at the base of a walking leg. The pH was immediately measured at the desired temperature with a Radiometer G292/G2 pH microelectrode, and Pco2 was measured indirectly by the Astrup interpolation method (Truchot, 1973).
RESULTS
(1) Duration for acclimation to new ambient conditions Table 1 shows that after 16 hr of exposure to new ambient conditions of temperature, pH, I’,,, and I’%, the acid-base balance reached a new steady state, since the values observed after one or two days more did not differ from those observed after 1623 hr exposure. The values measured in the afternoon were the same as those measured in the morning, in this or other experimenta series. acid-base balance in animals exposed at I, 16 or 25°C in isobaric normoxia or in isoconcentration normoxia
As Fig. 2 shows, the fali of pH with the increase of temperature from 7 to 25°C is nearly identical in both series, namely in animals subjected to changes of temperature at constant 0, pressure (158 torr; isobaric normoxia) or at constant Q2 isoconcentration (0.252 mmol 1-l; isoconcentration normoxia). It is practically impossible to differentiate graphically the two lines joining the pH values at 7 and 25°C which differ by 0.02 pH unit at the most. Table 1. Duration for acclimation of the crab hemolymph acid-base balance (ABB) to new ambient conditions. On 2 August, the animals maintained in an air-bubbled storage tank at 1%16°C were immersed in the experimental tank at 7°C Po, = 131.5 ton, P co2 = 0.82 torr, pH = 7.72 (point h’ of Fig. 1). On 3, 4 and 5 August, the ABB of the prebranchial hemolymph was determined
Fig. 1. Concentration of oxygen, Co,, as a function of PO, in seawater at 7, 16 and 25°C. The isotherms at 7 and 25°C are drawn in. Insert indicates the 0, solubility, the O* partial pressure and concentration, PO, and Co,, at 7, 16 and 27°C and the meaning of the symbols. There are three points (N’, N16 and Nz5) at the same normoxic pressure of 158 torr (isoPoJ and three points (h’, Nib and H2’) at the same normoxic concentration of 0.252 mm01 ll’(isoCoJ.
1983 2 August 1983 3 August (16-23 hr) 1983 4 August (39-47 hr) 1983 5 August (63-71 hr)
n
Pm
Start at 6 p.m. 10 am-5 p.m.
12
9 a.m.-5 p.m.
12
9 am-5
12
7.885 0.021 7.889 0.017 7.900 0.015
p.m.
pii,,, (torr) 2.59 0.15 2.70 0.18
2.47 0.08
In parentheses the duration of exposure. n = number of animals. In italics, 1 SEM.
261
Crab hemolymph acid-base balance Pco2
change is about twice as high in the O2 isoconcentration temperature change (h’-H*‘) as in the O2 isobaric temperature change (w-N*‘). One may variations from h7 to H25 as a consider the P,, succession of steps (Fig. 2): h7 to N7, in which Pco2 increases because of the slight ventilatory depression related to the increase in PO,; an O,-isobaric thermal
7
10
15
20 Temperature ‘C
25
Fig. 2. Carbon dioxide partial pressure, PG,,, and pm of the prebranchial hemolymph of the crab exposed for at least 40 hr to the 0, isobaric conditions h’, N”j, Hz5 or to the 0, isoconcentration conditions N’, N16 and N25, as defined in Fig. 1. Mean values of measurements on 12 crabs. Two standard errors on each side of the Ni6 points.
Their mean slope is -0.0149
pH unit.‘C-’
(-0.0144
for the isococcentration slope and -0.0153 for the isobaric slope). The point N16which by convention is normoxic for both oxygen pressure and concentration is outside the range defined by the line joining the points at 7 and 25°C. However, whereas the slopes pH vs T are nearly identical in both kinds of normoxia, the change of Pco2 and consequently the change of carbonate concentration differ markedly. At a given temperature, 7 or 25°C from points h’ to N’ and from points Nz5 to H25, that is for an increase of PO, from 131.5 (h’) to 158 torr (N7) and an increase from 158 torr (N25) to 183.9 torr (H*‘), Pco2 increased by 0.36 torr at 7°C (P < 0.05) and by 0.51 torr at 25°C (P < 0.01). The compounded increase of Pco, in going from point h7 to point H25was 1.68 torr, due partly to the higher O2 pressure and partly to the higher temperature. DISCUSSION
A new acid-base balance was reached within 16 hr (Table 1) when the ambient conditions (temperature, and PO,) were changed. This observation P cz%lrms that the compensation of the ABB disturbance is rapid in the shore crab (Truchot, 1975a). These experiments were performed because (1) variations of water oxygenation change the ventilation and the ABB of aquatic animals (Dejours, 1975; Truchot, 1981); (2) at constant P,-pl the temperature changes the water O2 concentration; (3) the temperature-induced O2 concentration changes strongly affect the change of the acid-base balance with temperature in another decapod crustacean, the freshwater crayfish Astacus leptodactylus (Dejours and Armand, 1983). Our observations in Carcinus maenas differ markedly from those in Astacus Zeptodactylus. In the crayfish the pH change with temperature at constant O2 concentration is much greater than that at constant 0, pressure, whereas in Carcinus mamas the pH change is almost exactly the same in both conditions. However, in Carcinus, the CBPA 81/2-D
change N’ to N25; and finally the step N25 to H25 in which the O2 concentration prevailing at h’ is reached, a step that entails a small hypercapnia as in the step h7 to N7. The fact that, in Carcinus, pH is the same in h’ and N7 on the one hand, and in N25 and H25on the other, implies that the increase of Pco, due to the hypercapnic steps caused by the small increase of oxygenation (h’-N7 and N25-H25) is completely compensated by a concomitant increase in carbonates. It is not known whether this difference in the ABB behavior imposed by the conditions is a phenomenon common to all freshwater and marine decapods. The acid-base balance in the freshwater decapod is greatly influenced by the chloride content of the water (Dejours et al., 1982; Dejours, 1983). The marine Carcinus lives in a very Cl-rich milieu, a fact which may explain why its ABB change is perfectly compensated. The general conclusion to be drawn from this study is almost a truism; for all physiological studies in respiration and acid-base balance, an essential experimental prerequisite is an excellent regulation of ambient PO,, ionic composition, ABB and temperature. Acknowledgements-The authors thank Mrs Sarah Dejours for editing the English of this manuscript. REFERENCES
Dejours P. (1975) Principles of Comparative Respiratory Physiology, 2nd ed, 1981. Elsevier/North-Holland, Amsterdam. Dejours P. (1983) The haemolymph acid-base of the crayfish Astacus leptodactylzu as a function of the ambient water acid-base balance and its chloride concentration. J. Physiol. Lond. 345, 31P. Dejours P. and Armand J. (1980) Hemolymph acid-base balance of the crayfish Astacus leptodactylus as a function of the oxygenation and the acid-base balance of the ambient water. Resp. Physiol. 41, l-l 1. Dejours P. and Armand J. (1983) Acid-base balance of crayfish hemolymph: effects of simultaneous changes of ambient temperature and water oxygenation. J. camp. Physiol. 149, 463468.
Dejours P., Armand J. and Beekenkamp H. (1982) The effect of ambient chloride concentration changes on branchial chloride-bicarbonate exchanges and hemolymph acid-base balance of crayfish Resp. Physiol. 48,373-386. Heisler N. (1981) Regulation of the acid-base status in fishes. In Environmental Physiology of Fishes (Edited by Ali M. A.), pp. 123-199. Plenum Press, New York. Rahn H. and Howell B. J. (1978) The OH-/H” concept of acid-base balance: historical development. Resp. Physiol. 33, 91-97. Rahn H., Reeves R. B. and Howell B. J. (1975) Hydrogen ion regulation, temperature and evolution. Am. Rev. Resp. Dis. 112, 165-172. Reeves R. B. (1977) The interaction of body temperature and acid-base balance in ectothermic vertebrates. A. Rev. Physiol. 39, 559-586.
262
P. DEJOURS et al.
Somero G. N. (1981) pH-temperature interaction on proteins: principles of optimum pH and buffer system design. Mar. Biol. Lett. 2, 163-178. Truchot J.-P. (1973) Temperature and acid-base regulation in the shore crab, Carciks maenas (L.). Resp. Phy>iol. 17, 1 l-20. Truchot J.-P. (1975a) Action de l’hypercapnie sur Mat acide-base du sang chez le crabe Curcinus maenas (L.)
(Crustace dtcapode). C.V. Acad. Sci. Paris 280, @Brie D), 311-314. Truchot J.-P. (1975b) Blood acid-base changes during experimental emersion and reimmersion of the intertidal crab Carcinus maenas (L.). Resp. Physiol. 23, 351-360. Truchot J.-P. (1981) L’bouilibre acido-basique extracellulaire et sa regulation dans les divers groupes d’animaux. J. Physiol. Paris 77, 529-580.
81A, No. 2, pp. 259-262, 1985
0300-9629/85$3.00+ 0.00 0 1985Pergamon Press Ltd
Printed in Great Britain
EFFECTS OF SIMULTANEOUS CHANGES OF WATER TEMPERATURE AND OXYGENATION ON THE ACID-BASE BALANCE OF THE SHORE CRAB, CARCINUS MAENAS P. DEJOURS*,A. TOULMOND~ and J.-P. TRUCHOT~ Station Biologique, Roscoff, France (Received 5 October 1984) Abstract-l. Shore crabs Curcinus maenas were exposed to constant normoxic Po, (isobaric normoxia) or constant normoxic Co, (isoconcentration normoxia), at ambient seawater temperature of 7, 16 and 25”C, and constant Pco,, 0.82 torr. The acid-base balance (ABB) of prebranchial hemolymph was assessed by measuring pH and P,!. 2. The pHi-temperature relationship was the same in isobaric and isoconcentration normoxia, but the temperature-dependent variations of fico2 were more marked in the second condition. This implies that the hemolymph carbonate concentration variations paralleled the P’Eco2changes. 3. By contrast, in the freshwater decapod crayfish Astacus leptodactylus, temperature-dependent changes of fiCO? and carbonate concentration are different in isobaric and isoconcentration normoxia. 4. In studies of respiration and ABB of water breathers, an essential prerequisite is an excellent regulation of ambient PO,, Pco,, ionic composition and temperature, because, as these experiments illustrate, the changes of ABB with ambient temperature variation are influenced by the effect of temperature on the ambient 0, concentration, which itself also contributes to the observed respiratory and ABB responses.
the saturating water vapor pressure with the increase of the temperature. The conclusion was that a decrease of hemolymph pH with a rise in temperature at constant PO, is partially offset by the concomitant decrease of water Co,. At constant PO,, the pH vs temperature slope was -0.008 pH unit .“C-‘; at constant CoZ the mean slope was -0.014 pH unit. “C- ’ . Here, we examine whether the marine decapod, the shore crab Carcinus maenas, behaves like the freshwater crayfish. The hemolymph ABB of shore crabs was measured as a function of temperature either at constant Pco,, or at constant Co,. The results in the crab are different from those in the crayfish, but they do show that the ABB variations with temperature are not the same in 0, isoconcentration normoxia and in isobaric normoxia.
INTRODUCTION For about twenty years the effects of variations
of the
ambient temperature on blood acid-base balance (ABB) have been intensively studied. Recent reviews include Rahn et ~2. (1975), Reeves (1977), Heisler (1981), Somero (1981) and Rahn and Howell (1978). The main results may be thus summarized: in poikilotherms, the blood pH decreases with an increase of temperature, an almost linear relation with an average slope of -0.017 pH unit.“C-‘. The slope of the neutral water pH vs temperature is nearly the same. Blood pH is always higher than water pH. But there are some exceptions among air and water breathers (see for references Dejours and Armand, 1983). These authors have sought to see, in the crayfish Astacus leptodactylus, if the changes of ABB with temperature could be entirely ascribed to thermal change, or if they were somewhat influenced by the effect of temperature variations in air-equilibrated water on the water O2 concentration. The O2 concentration could be affected for two reasons: (1) principally the decrease of O2 solubility with increase of temperature; (2) to a lesser extent, the decrease of the O2 partial pressure, PO,, in the gas phase (and thus in the air-equilibrated water) because of the increase of
MATERIALS AND METHODS Two series of experiments were conducted in the summer of 1983 at the Roscoff Biological Station in Brittany, France. We here report one series; the other gave nearly identical results. Control of the ambient conditions in the water bath
*Laboratoire de Physiologie Respiratoire, CNRS, 23 rue Becquerel, 67087 Strashourg, France. TBiologie et Physiologie des Organismes Marins, UniversitC Pierre-et-Marie-Curie, 4 place Jussieu, 75230 Paris 5, France. $.Station Marine, Laboratorie de Neurobiologie et Physiologie Comparkes, 2 rue du Professeur Jolyet, 33120 Arcachon, France.
We used a 55 liter rectangular tank, about 18 cm deep; the animals were prevented from surfacing since emersion entails respiratory acidosis (Truchot, 1975b). The tank water was renewed at a rate of about 0.2 I’min-’ and vigorously agitated by (1) an intense bubbling at various tank sites, (2) an external pump which recycled the water at a rate of 4 I’min-‘. The water was then satisfactorily homogenous, as demonstrated by temperature (and eventually P,, and pH) measurements at different tank sites. The seawater salinity was 35.06%0 and titration alkalinity 2.44 meq’l-‘. In this water three ambient factors were
259
260
P. DEJOURS et al.
regulated, namely temperature, Po, and pH (which implies a regulation of the whole carbonic system since TA was virtually constant). Temperature. The water was thermostatically controlled at 7, 16 or 25°C + 0.5”C. The source of cold or warm water was located outside the tank and fed a glass and rubber heat exchanger located in a side compartment of the tank. Oxygenation. Experiments were performed in one of the two conditions: (1) either Po, was maintained constant at a value of a few torrs above the actual ambient Paz which varies with the barometric pressure and the water vapor tension: arbitrarily the normoxic Po, was fixed at 158 torr; (2) or oxygen concentration, Co,, was maintained constant at the value prevailing at 16°C when the Po, value was 158 torr, namely 0.252 mmol.l-‘. For water temperatures at 7 and 25°C the chosen PO2 value took into account the 0, solubility decrease with the increase of temperature, namely Po, = 131.5 torr for 7°C and PO, = 183.9 torr at 25°C (Fig. 1). Thus we worked either at normoxic 0, tensions of 158 torr whatever the temperature (N’, Ni6, N2$ that is in isobaric normoxia, or at the normoxic oxygenation concentrations of 0.252mmol.l-’ (h7, Nn’, H”‘) which may be called isoconcentration normoxia (Fig. 1). PO, was fixed at the values of 158, 131.5 or 183.9 torr by means of an O,-stat which, by a system identical in principle to a pH-CO?-stat (Dejours and Armand, 1980) admits a proper amount of N, in order to fix water PO2 at 131.5 or admits O? to fix water PO2 at 183.9 torr. The PO, values were checked regularly during the experimental session and varied within a range of +3 torr. Acid-base balance. The water ABB was regulated by a pH-CO,-stat (Dejours and Armand, 1980) such that P,,, was about 0.82 torr. Seawater was equiiibrated at 7, 16 or 25°C with a CO,-containing mixture (about 0.82 torr), delivered by a Wiisthoff pump; the pH values of these waters, 7.72, 7.75 and 7.82, respectively, were then measured and used as set points of the pH-CO,-stat. The figures the water tank pH-CO,-stat displayed were arbitrary units chosen so that the actual pH measured with excellent reproducibility by a calibrated pH electrode was within +0.02 pH unit of the above values.
1. Duration for acclimation to new ambient conditions. Forty crabs kept in air-equilibrated seawater at 15-16°C were placed in an h’ water (Fig. 1) that is at 7°C with a Po?, P cOz and pH of about 131.5 torr, 0.82 torr and 7.82. The next day, after at least 16 hr of exposure to the h’ conditions, the hemolymph ABB of 12 crabs was determined. The same procedure was renewed after one and two days more of exposure. Thus there were three groups of 12 animals each exposed for at least 15, 40 or 60 hr, namely h:, hi and hi. As will be seen below, 16 hr was sufficient to reach a new ABB steady state. 2. The hemolymph acid-base balance in animals exposed to 7, 16 or 25°C in isobaric normoxia or in isoconcentration normoxie. Fifteen crabs were immersed in the late afternoon in a tank with the required temperature, pH (PcOJ and Po, of acclimation. These animals were studied after at least 40 hr of exposure, although 16 hr would have been enough. We measured hemolymph of 12 animals only; the extra animals constituted a reserve in case hemolymph samplings were defective.
Protocol
(2) The hemolymph
The experimental animals were kept in a large, wellaerated tank in which the seawater was continuously renewed at a temperature of 15-l 6°C. They were fed every day with fresh limpets.
Hemolymph acid-base balance measurements Hemolymph was sampled anaerobically at the base of a walking leg. The pH was immediately measured at the desired temperature with a Radiometer G292/G2 pH microelectrode, and Pco2 was measured indirectly by the Astrup interpolation method (Truchot, 1973).
RESULTS
(1) Duration for acclimation to new ambient conditions Table 1 shows that after 16 hr of exposure to new ambient conditions of temperature, pH, I’,,, and I’%, the acid-base balance reached a new steady state, since the values observed after one or two days more did not differ from those observed after 1623 hr exposure. The values measured in the afternoon were the same as those measured in the morning, in this or other experimenta series. acid-base balance in animals exposed at I, 16 or 25°C in isobaric normoxia or in isoconcentration normoxia
As Fig. 2 shows, the fali of pH with the increase of temperature from 7 to 25°C is nearly identical in both series, namely in animals subjected to changes of temperature at constant 0, pressure (158 torr; isobaric normoxia) or at constant Q2 isoconcentration (0.252 mmol 1-l; isoconcentration normoxia). It is practically impossible to differentiate graphically the two lines joining the pH values at 7 and 25°C which differ by 0.02 pH unit at the most. Table 1. Duration for acclimation of the crab hemolymph acid-base balance (ABB) to new ambient conditions. On 2 August, the animals maintained in an air-bubbled storage tank at 1%16°C were immersed in the experimental tank at 7°C Po, = 131.5 ton, P co2 = 0.82 torr, pH = 7.72 (point h’ of Fig. 1). On 3, 4 and 5 August, the ABB of the prebranchial hemolymph was determined
Fig. 1. Concentration of oxygen, Co,, as a function of PO, in seawater at 7, 16 and 25°C. The isotherms at 7 and 25°C are drawn in. Insert indicates the 0, solubility, the O* partial pressure and concentration, PO, and Co,, at 7, 16 and 27°C and the meaning of the symbols. There are three points (N’, N16 and Nz5) at the same normoxic pressure of 158 torr (isoPoJ and three points (h’, Nib and H2’) at the same normoxic concentration of 0.252 mm01 ll’(isoCoJ.
1983 2 August 1983 3 August (16-23 hr) 1983 4 August (39-47 hr) 1983 5 August (63-71 hr)
n
Pm
Start at 6 p.m. 10 am-5 p.m.
12
9 a.m.-5 p.m.
12
9 am-5
12
7.885 0.021 7.889 0.017 7.900 0.015
p.m.
pii,,, (torr) 2.59 0.15 2.70 0.18
2.47 0.08
In parentheses the duration of exposure. n = number of animals. In italics, 1 SEM.
261
Crab hemolymph acid-base balance Pco2
change is about twice as high in the O2 isoconcentration temperature change (h’-H*‘) as in the O2 isobaric temperature change (w-N*‘). One may variations from h7 to H25 as a consider the P,, succession of steps (Fig. 2): h7 to N7, in which Pco2 increases because of the slight ventilatory depression related to the increase in PO,; an O,-isobaric thermal
7
10
15
20 Temperature ‘C
25
Fig. 2. Carbon dioxide partial pressure, PG,,, and pm of the prebranchial hemolymph of the crab exposed for at least 40 hr to the 0, isobaric conditions h’, N”j, Hz5 or to the 0, isoconcentration conditions N’, N16 and N25, as defined in Fig. 1. Mean values of measurements on 12 crabs. Two standard errors on each side of the Ni6 points.
Their mean slope is -0.0149
pH unit.‘C-’
(-0.0144
for the isococcentration slope and -0.0153 for the isobaric slope). The point N16which by convention is normoxic for both oxygen pressure and concentration is outside the range defined by the line joining the points at 7 and 25°C. However, whereas the slopes pH vs T are nearly identical in both kinds of normoxia, the change of Pco2 and consequently the change of carbonate concentration differ markedly. At a given temperature, 7 or 25°C from points h’ to N’ and from points Nz5 to H25, that is for an increase of PO, from 131.5 (h’) to 158 torr (N7) and an increase from 158 torr (N25) to 183.9 torr (H*‘), Pco2 increased by 0.36 torr at 7°C (P < 0.05) and by 0.51 torr at 25°C (P < 0.01). The compounded increase of Pco, in going from point h7 to point H25was 1.68 torr, due partly to the higher O2 pressure and partly to the higher temperature. DISCUSSION
A new acid-base balance was reached within 16 hr (Table 1) when the ambient conditions (temperature, and PO,) were changed. This observation P cz%lrms that the compensation of the ABB disturbance is rapid in the shore crab (Truchot, 1975a). These experiments were performed because (1) variations of water oxygenation change the ventilation and the ABB of aquatic animals (Dejours, 1975; Truchot, 1981); (2) at constant P,-pl the temperature changes the water O2 concentration; (3) the temperature-induced O2 concentration changes strongly affect the change of the acid-base balance with temperature in another decapod crustacean, the freshwater crayfish Astacus leptodactylus (Dejours and Armand, 1983). Our observations in Carcinus maenas differ markedly from those in Astacus Zeptodactylus. In the crayfish the pH change with temperature at constant O2 concentration is much greater than that at constant 0, pressure, whereas in Carcinus mamas the pH change is almost exactly the same in both conditions. However, in Carcinus, the CBPA 81/2-D
change N’ to N25; and finally the step N25 to H25 in which the O2 concentration prevailing at h’ is reached, a step that entails a small hypercapnia as in the step h7 to N7. The fact that, in Carcinus, pH is the same in h’ and N7 on the one hand, and in N25 and H25on the other, implies that the increase of Pco, due to the hypercapnic steps caused by the small increase of oxygenation (h’-N7 and N25-H25) is completely compensated by a concomitant increase in carbonates. It is not known whether this difference in the ABB behavior imposed by the conditions is a phenomenon common to all freshwater and marine decapods. The acid-base balance in the freshwater decapod is greatly influenced by the chloride content of the water (Dejours et al., 1982; Dejours, 1983). The marine Carcinus lives in a very Cl-rich milieu, a fact which may explain why its ABB change is perfectly compensated. The general conclusion to be drawn from this study is almost a truism; for all physiological studies in respiration and acid-base balance, an essential experimental prerequisite is an excellent regulation of ambient PO,, ionic composition, ABB and temperature. Acknowledgements-The authors thank Mrs Sarah Dejours for editing the English of this manuscript. REFERENCES
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