scholarly journals Transbranchial ammonia gradients and acid-base responses to high external ammonia concentration in rainbow trout (Oncorhynchus mykiss) acclimated to different salinities

1992 ◽  
Vol 166 (1) ◽  
pp. 95-112 ◽  
Author(s):  
R. W. Wilson ◽  
E. W. Taylor
Keyword(s):  
Rainbow Trout ◽  
Sea Water ◽  
Ammonia Excretion ◽  
Ammonia Concentration ◽  
Acid Base ◽  
Experimental Conditions ◽  
Rainbow Trout Oncorhynchus Mykiss ◽  
Total Ammonia ◽  
Acid Base Status ◽  
The Difference

Transbranchial ammonia gradients and blood acid-base status have been examined in rainbow trout acclimated to fresh water (FW), 33% sea water (33% SW) and sea water (SW) and exposed to 1.0 mmol l-1 total ammonia (TAmm) at pH 7.9 for 24 h. At all three salinities trout maintained large negative (inwardly directed) NH3 and NH4+ gradients throughout the exposure, presumably by active excretion of NH4+ to counteract the passive inward diffusion of ammonia. Analysis of blood non-respiratory acid-base status (delta H+m) revealed an acid load in FW trout and a base load in SW trout following 24 h of exposure. This indicates that active NH4+/H+ exchange predominates in FW whereas NH4+/Na+ is the principal exchange utilised in SW under these experimental conditions. The plasma TAmm load incurred during ammonia exposure increased with salinity. Compared to FW trout, plasma TAmm values were 34 and 73% higher in the 33% SW and SW trout, respectively, after 24 h. This cannot be explained by differences in the prevailing transbranchial PNH3 gradient because ambient PNH3 was substantially lower at the higher salinities (due to higher pK' and solubility values). We interpret the difference between FW and SW trout as an increased permeability to NH4+ in fish acclimated to the higher-salinity environments. Transbranchial diffusion of NH4+ is, therefore, probably more important as a route for ammonia excretion in SW than in FW trout, especially considering the favourable transepithelial potentials normally found in SW teleosts. In addition, increased NH4+ permeability implies that the toxicity of ammonia will be greater in seawater than in freshwater teleosts and should not simply be measured as a function of the unionised ammonia concentration when considering seawater-adapted species.

Effect Of Environmental Water Salinity on Acid-Base Regulation During Environmental Hypercapnia in the Rainbow Trout (Oncorhynchus Mykiss)

1991 ◽  
Vol 158 (1) ◽  
pp. 1-18 ◽  
Author(s):  
GEORGE K. IWAMA ◽  
NORBERT HEISLER
Keyword(s):  
Rainbow Trout ◽  
Respiratory Acidosis ◽  
Environmental Water ◽  
Ammonia Concentration ◽  
Acid Base ◽  
Clear Trend ◽  
Rainbow Trout Oncorhynchus Mykiss ◽  
Exchange Processes ◽  
Total Ammonia ◽  
Time Courses

Acid-base regulation in rainbow trout acclimated to about 3, 100 and 500 mmol l−1 Na+ and Cl−, at constant water [HCO3−], was assessed during 24h of exposure to 1% CO2 and during recovery. The respiratory acidosis induced by a rise in plasma PCOCO2 to about 1.15kPa (8.5mmHg, 3mmol l−1), 1.33kPa (10mmHg, 100 mmol l−1) or 1.5 kPa (11.2 mmHg, 500 mmol l−1) was partially compensated for by accumulation of plasma HCO3−. The degree of pH compensation depended on the salinity of the environmental water, being about 61, 82 and 88% at 3, 100 and 300 mmol l−1 Na+ and Cl−, respectively. [HCO3−] in animals acclimated to 100 and 500 mmol l−1 rose to higher values than that in fish at 3 mmol l−1. Plasma [Cl−] decreased during hypercapnia as compared to control concentrations in all groups of fish. Plasma [Na+] rose during the first 8 h of hypercapnia in fish acclimated to all three salinities, but recovered towards control values during the remainder of hypercapnia. The rise in plasma [HCO3−] was significantly related to the fall in plasma [Cl−], whereas the changes in plasma [Na+] were unaffected by simultaneous changes in plasma [HCO3−]. Time courses of changes in plasma [Na+] and total ammonia concentration, [Tamm], were similar but in opposite directions. The transepithelial potential (TEP) of blood relative to water was negative, close to zero and positive, averaging −21, −5.8 and +6.2 mV for fish acclimated to 3, 100 and 300 mmol l−1 Na+, respectively. After initiation of hypercapnia, which caused a quite heterogeneous response among groups, a clear trend towards depolarization was observed during the remainder of hypercapnia. These results confirm the role of active HCO3−/Cl− exchange processes for the compensation of extracellular pH during respiratory acidoses in fish.

White Muscle Intracellular Acid-Base and Lactate Status Following Exhaustive Exercise: A Comparison between Freshwater- and Sea Water- Adapted Rainbow Trout

1991 ◽  
Vol 156 (1) ◽  
pp. 153-171 ◽  
Author(s):  
YONG TANG ◽  
ROBERT G. BOUTILIER
Keyword(s):  
Rainbow Trout ◽  
White Muscle ◽  
Sea Water ◽  
Ph Regulation ◽  
Recovery Period ◽  
Exhaustive Exercise ◽  
Acid Base ◽  
Post Exercise ◽  
Acid Base Status ◽  
Intracellular Acid

The intracellular acid-base status of white muscle of freshwater (FW) and seawater (SW) -adapted rainbow trout was examined before and after exhaustive exercise. Exhaustive exercise resulted in a pronounced intracellular acidosis with a greater pH drop in SW (0.82 pH units) than in FW (0.66 pH units) trout; this was accompanied by a marked rise in intracellular lactate levels, with more pronounced increases occurring in SW (54.4 mmoll−1) than in FW (45.7 mmoll−1) trout. Despite the more severe acidosis, recovery was faster in the SW animals, as indicated by a more rapid clearance of metabolic H+ and lactate loads. Compartmental analysis of the distribution of metabolic H+ and lactate loads showed that the more rapid recovery of pH in SW trout could be due to (1) their greater facility for excreting H+ equivalents to the environmental water [e.g. 15.5 % (SW) vs 5.0 % (FW) of the initial H+ load was stored in external water at 250 min post-exercise] and, to a greater extent, (2) the more rapid removal of H+, facilitated via lactate metabolism in situ (white muscle) and/or the Cori cycle (e.g. heart, liver). The slower pH recovery in FW trout may also be due in part to greater production of an ‘unmeasured acid’ [maximum approx. 8.5 mmol kg−1 fish (FW) vs approx. 6 mmol kg−1 fish (SW) at 70–130 min post-exercise] during the recovery period. Furthermore, the analysis revealed that H+-consuming metabolism is quantitatively the most important mechanism for the correction of an endogenously originating acidosis, and that extracellular pH normalization gains priority over intracellular pH regulation during recovery of acid-base status following exhaustive exercise.

scholarly journals THE EFFECTS OF HYPOXIA, HYPEROXIA OR HYPERCAPNIA ON THE ACID-BASE DISEQUILIBRIUM IN THE ARTERIAL BLOOD OF RAINBOW TROUT

1994 ◽  
Vol 192 (1) ◽  
pp. 269-284 ◽  
Author(s):  
K Gilmour ◽  
S Perry
Keyword(s):  
Rainbow Trout ◽  
Partial Pressure ◽  
Co2 Uptake ◽  
Acid Base ◽  
Experimental Conditions ◽  
Directed Diffusion ◽  
Rainbow Trout Oncorhynchus Mykiss ◽  
External Loop ◽  
Arterial Blood ◽  
Co2 Excretion

An extracorporeal circulation in combination with a stop­flow technique was used to characterize the acid­base disequilibrium in the arterial blood of rainbow trout Oncorhynchus mykiss during environmental hypoxia, hyperoxia or hypercapnia. Arterial blood was routed from the coeliac artery through an external circuit in which pH (pHa), partial pressure of oxygen (PaO2) and partial pressure of carbon dioxide (PaCO2) were monitored continuously. The stop­flow condition was imposed by turning off the pump which drove the external loop. Water PO2 or PCO2 was adjusted to give the experimental conditions by bubbling N2, O2 or CO2 through a water equilibration column supplying the fish. During normoxia, the arterial blood exhibited a positive acid­base disequilibrium of approximately 0.04 pH units; that is, pH increased over the stop­flow period by 0.04 units. The extent of the imbalance was increased significantly by hypoxia (final PaO2=2.7­3.7 kPa; deltapH=0.05 units). In fish exposed to hyperoxia (final PaO2=47­67 kPa), the direction of the disequilibrium was reversed; pHa declined by 0.03 units. During hyperoxia, CO2 excretion was impaired by 63 % and the PCO2 of postbranchial blood was higher than that of prebranchial blood. It is therefore conceivable that a reversal of the normal, outwardly directed, diffusion gradient for CO2 accounted for the negative disequilibrium; CO2 uptake at the gills would drive plasma CO2/HCO3-/H+ reactions towards CO2 hydration and H+ formation. During hypercapnia, fish exhibited a twofold increase in the positive pH disequilibrium (deltapH=0.06 units). The results of this study confirmed the existence of an acid­base disequilibrium in the arterial blood of rainbow trout and clearly demonstrated that the extent and/or direction of the disequilibrium are influenced by the respiratory status of the fish.

The linkage between Na+ uptake and ammonia excretion in rainbow trout: kinetic analysis, the effects of (NH4)2SO4 and NH4HCO3 infusion and the influence of gill boundary layer pH

1999 ◽  
Vol 202 (6) ◽  
pp. 697-709 ◽  
Author(s):  
A. Salama ◽  
I.J. Morgan ◽  
C.M. Wood
Keyword(s):  
Boundary Layer ◽  
Rainbow Trout ◽  
Kinetic Analysis ◽  
Dominant Role ◽  
Ammonia Excretion ◽  
Rainbow Trout Oncorhynchus Mykiss ◽  
Total Ammonia ◽  
Stimulation Of

The nature of the linkage between between branchial ammonia excretion (JAmm) and unidirectional Na+ influx (JNain) was studied in the freshwater rainbow trout (Oncorhynchus mykiss). Arterial plasma total [ammonia], PNH3 and JAmm were all elevated approximately threefold by intravascular infusion for 24 h with either 70 mmol l-1 (NH4)2SO4 or 140 mmol l-1 NH4HCO3 at a rate of approximately 400 micromol kg-1 h-1. Both treatments markedly stimulated JNain. NH4HCO3 induced metabolic alkalosis in the blood plasma, whereas (NH4)2SO4 caused a slight metabolic acidosis. Experiments with Hepes-buffered water (5 mmol l-1) under control conditions demonstrated that increases in gill boundary layer pH were associated with decreases in both JNain and JAmm. Thus, the stimulation of JNain caused by ammonium loading was not simply a consequence of a Na+-coupled H+ extrusion mechanism activated by internal acidosis or by alkalosis in the gill boundary layer. Indeed, there was no stimulation of net acidic equivalent excretion accompanying NH4HCO3 infusion. Michaelis-Menten kinetic analysis by acute variation of water [Na+] demonstrated that both infusions caused an almost twofold increase in JNamax but no significant change in Km, indicative of an increase in transporter number or internal counterion availability without an alteration in transporter affinity for external Na+. The increase in JNain was larger with (NH4)2SO4 than with NH4HCO3 infusion and in both cases lower than the increase in JAmm. Additional evidence of quantitative uncoupling was seen in the kinetics experiments, in which acute changes in JNain of up to threefold had negligible effects on JAmm under either control or ammonium-loaded conditions. In vitro measurements of branchial Na+/K+-ATPase activity demonstrated no effect of NH4+ concentration over the concentration range observed in vivo in infused fish. Overall, these results are consistent with a dominant role for NH3 diffusion as the normal mechanism of ammonia excretion, but indicate that ammonium loading directly stimulates JNain, perhaps by activation of a non-obligatory Na+/NH4+ exchange rather than by an indirect effect (e.g. Na+-coupled H+ excretion) mediated by altered internal or external acid-base status.

The cultured branchial epithelium of the rainbow trout as a model for diffusive fluxes of ammonia across the fish gill

2001 ◽  
Vol 204 (23) ◽  
pp. 4115-4124
Author(s):  
Scott P. Kelly ◽  
Chris M. Wood
Keyword(s):  
Rainbow Trout ◽  
Fresh Water ◽  
Ammonia Excretion ◽  
Ammonia Concentration ◽  
Paracellular Permeability ◽  
Apical Surface ◽  
Ph Gradients ◽  
Rainbow Trout Oncorhynchus Mykiss ◽  
Diffusive Fluxes

SUMMARYA novel branchial epithelial preparation grown in L-15 medium in culture was used as a model system for understanding the diffusion of ammonia across the gills of the rainbow trout Oncorhynchus mykiss. The epithelium is known to contain both respiratory and mitochondria-rich cells in the approximate proportion in which they occur in vivo and to exhibit diffusive fluxes of Na+ and Cl– similar to in vivo values, but does not exhibit active apical-to-basolateral transport of Na+. Transepithelial resistance and paracellular permeability are also known to increase when the apical medium is changed from L-15 medium (symmetrical conditions) to fresh water (asymmetrical conditions). In the present study, net basolateral-to-apical ammonia fluxes increased as basolateral total ammonia concentration, basolateral-to-apical pH gradients and basolateral-to-apical PNH3 gradients were experimentally increased and were greater under asymmetrical than under symmetrical conditions. The slope of the relationship between ammonia flux and PNH3 gradient (i.e. NH3 permeability) was the same under both conditions and similar to values for other epithelia. The higher fluxes under asymmetrical conditions were explained by an apparent diffusive flux of NH4+ that was linearly correlated with transepithelial conductance and was probably explained by the higher electrochemical gradient and higher paracellular permeability when fresh water was present on the apical surface. In this situation, NH4+ diffusion was greater than NH3 diffusion under conditions representative of in vivo values, but overall fluxes amounted to only approximately 20 % of those in vivo. These results suggest that branchial ammonia excretion in the intact animal is unlikely to be explained by diffusion alone and, therefore, that carrier-mediated transport may play an important role.

AMMONIA EXCRETION IN FRESHWATER RAINBOW TROUT (ONCORHYNCHUS MYKISS) AND THE IMPORTANCE OF GILL BOUNDARY LAYER ACIDIFICATION: LACK OF EVIDENCE FOR Na+/NH4+ EXCHANGE

1994 ◽  
Vol 191 (1) ◽  
pp. 37-58 ◽  
Author(s):  
R Wilson ◽  
P Wright ◽  
S Munger ◽  
C Wood
Keyword(s):  
Boundary Layer ◽  
Rainbow Trout ◽  
Ammonia Excretion ◽  
Bulk Water ◽  
Experimental Conditions ◽  
Sodium Uptake ◽  
Hepes Buffer ◽  
Total Ammonia ◽  
High Concentrations

Net ammonia fluxes (JAmm) were measured in adult freshwater rainbow trout in vivo under a variety of conditions designed to inhibit unidirectional sodium uptake (JinNa; low external [NaCl], 10(-4) mol l-1 amiloride), alter transbranchial PNH3 and NH4+ gradients [24 h continuous (NH4)2SO4 infusion, or exposure to 1 mmol l-1 external total ammonia at pH 8] and prevent gill boundary layer acidification (5 mmol l-1 Hepes buffer). Inhibition of JinNa with amiloride or low external [NaCl] under normal conditions reduced JAmm by about 20 %, but did not prevent the net excretion of ammonia during exposure to high concentrations of external ammonia. Increasing the buffer capacity of the ventilatory water with Hepes buffer (pH 8) reduced JAmm by 36 % and abolished the effect of amiloride on ammonia excretion. No evidence could be found to support a directly coupled apical Na+/NH4+ exchange. We suggest that any dependence of ammonia excretion on sodium uptake is caused by alteration of transbranchial PNH3 gradients within the gill microenvironment secondary to changes in net H+ excretion. Under normal conditions (pH 8, low external ammonia) gill boundary layer acidification facilitates over one-third of the total ammonia excretion. During exposure to high concentrations of external ammonia in poorly buffered water, estimates of transbranchial PNH3 gradients from measurements of bulk water pH and total ammonia concentration (TAmm) may be grossly in error because of boundary layer acidification. Prevention of boundary layer acidification with Hepes buffer during exposure to high cocncentrations of external ammonia revealed that the local transbranchial PNH3 gradient at the gill may in fact be positive (blood to water), negating the need for an active NH4+ transport mechanism. In freshwater trout, NH3 diffusion may account for all ammonia excretion under all experimental conditions used in the present study.

Physiological and morphological regulation of acid–base status during hypercapnia in rainbow trout (Oncorhynchus mykiss)

1993 ◽  
Vol 71 (8) ◽  
pp. 1673-1680 ◽  
Author(s):  
Greg G. Goss ◽  
Steve F. Perry
Keyword(s):  
Rainbow Trout ◽  
Oncorhynchus Mykiss ◽  
Chloride Cell ◽  
Morphological Alteration ◽  
Acid Base ◽  
Rapid Reduction ◽  
Fractional Area ◽  
Rainbow Trout Oncorhynchus Mykiss ◽  
Positive Formula ◽  
Acid Base Status

A kinetic analysis (Michaelis constant (Km) and maximal flux (Jmax)) of the branchial Na+ and Cl− influx mechanisms, along with measurements of blood total CO2 content [Formula: see text], net acidic–basic equivalent fluxes, and gill chloride cell morphology, was performed using rainbow trout (Oncorhynchus mykiss) before, during, and after 96 h exposure to environmental hypercapnia (water [Formula: see text]; 1 torr = 133.3 kPa). Exposure to hypercapnia caused (i) a net acidic equivalent loss (negative [Formula: see text]) that was accounted for entirely by reductions in titratable alkalinity flux (JTA), (ii) an increase in [Formula: see text] from 8.4 ± 0.5 to 20.7 ± 0.4 mmol/L, and (iii) no alteration either in [Formula: see text], [Formula: see text], or [Formula: see text]; [Formula: see text] increased (affinity was reduced). Chloride cell fractional area was reduced by 40% from 174 250 ± 15 650 μm2/mm2 under control conditions to 104 329 ± 17 991 μm2/mm2 after 96 h of hypercapnia. In the posthypercapnic period, there was (i) a net acidic equivalent gain (positive [Formula: see text]) that was accounted for entirely by an elevation in JTA, (ii) a rapid reduction of blood [Formula: see text], (iii) an increase of chloride cell fractional area to control values (179 105 ± 35 233μm2/mm2), and (iv) increases and decreases in [Formula: see text] (564 ± 50 versus 224 ± 21 μmol∙kg−1∙h−1 in the prehypercapnic period) and [Formula: see text] (381 ± 85 versus 585 ± 92 μmol∙kg−1∙h−1), respectively. The results suggest that morphological alteration of the gill chloride cell fractional area is an important response to acid–base disturbances. The results are discussed with respect to the relative roles of morphological alteration of gill chloride cell fractional area and variation in internal substrate (HCO3−) in modifying branchial Cl−/HCO3− exchange for acid–base regulation.

Sweat ammonia excretion during submaximal cycling exercise

1991 ◽  
Vol 70 (1) ◽  
pp. 371-374 ◽  
Author(s):  
D. Czarnowski ◽  
J. Gorski
Keyword(s):  
Room Temperature ◽  
Ammonia Excretion ◽  
Ammonia Concentration ◽  
Ammonia Level ◽  
Bicycle Ergometer ◽  
Plasma Ammonia ◽  
Cold Room ◽  
Before And After ◽  
Total Ammonia ◽  
The Difference

This study was undertaken to investigate whether part of the ammonia formed during muscular exercise was excreted with the sweat. Male medical students volunteered for the experiment. They exercised 30 min on a bicycle ergometer at 80 and 40% of the predetermined maximal O2 uptake (VO2max). Exercise at 80% VO2max was performed twice, at room temperature (20 degrees C) and in a cold room (0 degrees C), whereas exercise at 40% was performed only at room temperature (20 degrees C). Blood was collected from the antecubital vein immediately before and after exercise. Sweat was collected from the hypogastric region by use of gauze pads. It was shown that the plasma ammonia level was elevated after exercise at 80% VO2max and remained stable after exercise at 40% VO2max. The volume of sweat produced during exercise at 80% VO2max at 20 degrees C was 428 +/- 138 ml and at 0 degrees C 245 +/- 86 ml and during exercise at 40% VO2max was 183 +/- 69 ml. The ammonia concentration in the sweat after exercise at 80% VO2max at 20 degrees C was 7,140 mumol/l and at 0 degrees C 11,816 mumol/l. After exercise at 40% VO2max, it was 2,076 mumol/l. The total ammonia lost through the sweat during exercise at 80% VO2max was similar at both temperatures, despite the difference in the sweat volume (at 20 degrees C, 3,360 +/- 2,080 mumol; at 0 degrees C, 3,310 +/- 1,250 mumol). During exercise at 40% VO2max, it was 350 +/- 230 mumol. These results show that part of ammonia formed during exercise is lost with sweat. The amount lost increases with increased work rate and the plasma ammonia concentration.

Does blood acid-base status modulate catecholamine secretion in the rainbow trout (Oncorhynchus mykiss)?

1998 ◽  
Vol 201 (22) ◽  
pp. 3085-3095 ◽  
Author(s):  
AE Julio ◽  
CJ Montpetit ◽  
SF Perry
Keyword(s):  
Rainbow Trout ◽  
Receptor Agonist ◽  
Catecholamine Release ◽  
Catecholamine Secretion ◽  
Acid Base ◽  
Rainbow Trout Oncorhynchus Mykiss ◽  
Acid Base Status ◽  
Catecholamine Levels

The direct and modulating effects of acidosis on catecholamine secretion in rainbow trout (Oncorhynchus mykiss) were assessed in vivo using cannulated fish and in situ using a perfused cardinal vein preparation. In situ, acidosis (a reduction in perfusate pH from 7.9 to 7.4) did not elicit catecholamine release or modulate the secretion of catecholamines evoked by the non-specific cholinergic receptor agonist carbachol (3x10(-7) to 10(-5 )mol kg-1) or the muscarinic receptor agonist pilocarpine (10(-7 )mol kg-1). Acidosis, however, significantly increased the secretion rates of noradrenaline and adrenaline in response to nicotine (10(-8) to 10(-7 )mol kg-1). In vivo, intra-arterial injections of nicotine (300-600 nmol kg-1) into normocapnic or moderately hypercapnic fish (water PCO2=5 mmHg or 0.67 kPa) caused a dose-dependent elevation of circulating catecholamine levels. At the highest dose of nicotine, the rise in plasma catecholamine levels was significantly enhanced in the hypercapnic fish. Acute hypoxia in vivo caused an abrupt release of catecholamines when arterial haemoglobin O2-saturation was reduced to approximately 55-60 %; this catecholamine release threshold during hypoxia was unaltered in hypercapnic fish. However, the hypoxia-induced catecholamine release was significantly greater in hypercapnic fish than in normocapnic fish. The results of this study suggest that blood acid-base status, while not influencing catecholamine secretion directly or influencing the blood O2 content threshold for catecholamine release during hypoxia, may modulate the secretory process specifically in response to nicotinic receptor stimulation of chromaffin cells.

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