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Yuen K Ip - One of the best experts on this subject based on the ideXlab platform.
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defense against environmental ammonia toxicity in the african lungfish Protopterus aethiopicus bimodal breathing skin ammonia permeability and urea synthesis
Aquatic Toxicology, 2007Co-Authors: Ai M Loong, Shit F Chew, Wai P Wong, Yuen K IpAbstract:Abstract This study aimed to determine how the African lungfish Protopterus aethiopicus defended against ammonia toxicity when confronted with high concentrations (30 or 100 mmol l −1 ) of environmental ammonia . Exposure to 100 mmol l −1 of NH 4 Cl for 1 or 6 days had no significant effect on the rate of O 2 uptake from water or from air, and the rate of total O 2 consumption. Using an Ussing-like apparatus, we report for the first time that the skin of P. aethiopicus had low permeability (1.26 × 10 −4 μmol min −1 cm −1 ) to NH 3 in vitro . Indeed, the influx of exogenous ammonia into fish exposed to 30 mmol l −1 NH 4 Cl was low (0.117 μmol min −1 100 g −1 fish). As a result, P. aethiopicus could afford to maintain relatively low ammonia contents in plasma, muscle, liver and brain even after 6 days of exposure to 100 mmol l −1 NH 4 Cl. Surprisingly, fish exposed to 30 or 100 mmol l −1 NH 4 Cl had comparable ammonia contents in the muscle and the brain in spite of the big difference (70 mmol l −1 ) in environmental ammonia concentrations. Significant increases in urea contents occurred in various tissues of fish exposed to 30 mmol l −1 NH 4 Cl for 6 days, but there were no significant differences in tissue urea contents between fish exposed to 30 mmol l −1 and 100 mmol l −1 NH 4 Cl. Between days 3 and 6, the rate of urea excretion in fish exposed to 30 mmol l −1 NH 4 Cl was significantly greater than that of the control. By contrast, there was no significant difference in urea excretion rates between fish exposed to 100 mmol l −1 NH 4 Cl and control fish throughout the 6-day period, and such a phenomenon has not been reported before for other lungfish species. Thus, our results suggest that P. aethiopicus was capable of decreasing the NH 3 permeability of its body surface when exposed to high concentrations of environmental ammonia. Indeed, after 6 days of exposure to 100 mmol l −1 NH 4 Cl, the NH 3 permeability constant of the skin (0.55 × 10 −4 μmol min −1 cm −1 ) decreased to half of that of the control. A decrease in the already low cutaneous NH 3 permeability and an increased urea synthesis, working in combination, allowed P. aethiopicus to effectively defend against environmental ammonia toxicity without elevating the plasma ammonia level. Therefore, unlike other fishes, glutamine and alanine contents did not increase in the muscle and liver, and there was no accumulation of glutamine in the brain, even when the fish was immersed in water containing 100 mmol l −1 NH 4 Cl.
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the interplay of increased urea synthesis and reduced ammonia production in the african lungfish Protopterus aethiopicus during 46 days of aestivation in a mucus cocoon
Journal of Experimental Zoology Part A: Comparative Experimental Biology, 2005Co-Authors: Yuen K Ip, Ai M Loong, Kum C Hiong, Wai Peng Wong, Shit F ChewAbstract:This study was undertaken to test the hypothesis that the rate of urea synthesis in Protopterus aethiopicus was up-regulated to detoxify ammonia during the initial phase of aestivation in air (day 1–day 12), and that a profound suppression of ammonia production occurred at a later phase of aestivation (day 35–day 46) which eliminated the need to sustain the increased rate of urea synthesis. Fasting apparently led to a greater rate of nitrogenous waste excretion in P. aethiopicus in water, which is an indication of increases in production of endogenous ammonia and urea probably as a result of increased proteolysis and amino acid catabolism for energy production. However, 46 days of fasting had no significant effects on the ammonia or urea contents in the muscle, liver, plasma and brain. In contrast, there were significant decreases in the muscle ammonia content in fish after 12, 34 or 46 days of aestivation in air when compared with fish fasting in water. Ammonia was apparently detoxified to urea because urea contents in the muscle, liver, plasma and brain of P. aethiopicus aestivated for 12, 34 or 46 days were significantly greater than the corresponding fasting control; the greatest increases in urea contents occurred during the initial 12 days. There were also significant increases in activities of some of the hepatic ornithine–urea cycle enzymes from fish aestivated for 12 or 46 days. Therefore, contrary to a previous report on P. aethiopicus, our results demonstrated an increase in the estimated rate of urea synthesis (2.8-fold greater than the day 0 fish) in this lungfish during the initial 12 days of aestivation. However, the estimated rate of urea synthesis decreased significantly during the next 34 days. Between day 35 and day 46 (12 days), urea synthesis apparently decreased to 42% of the day 0 control value, and this is the first report of such a phenomenon in African lungfish undergoing aestivation. On the other hand, the estimated rate of ammonia production in P. aethiopicus increased slightly (14.7%) during the initial 12 days of aestivation as compared with that in the day 0 fish. By contrast, the estimated rate of ammonia production decreased by 84% during the final 12 days of aestivation (day 35–day 46) compared with the day 0 value. Therefore, it can be concluded that P. aethiopicus depended mainly on increased urea synthesis to ameliorate ammonia toxicity during the initial phase of aestivation, but during prolonged aestivation, it suppressed ammonia production profoundly, eliminating the need to increase urea synthesis which is energy-intensive. J. Exp. Zool. 303A:1054–1065, 2005. © 2005 Wiley-Liss, Inc.
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ornithine urea cycle and urea synthesis in african lungfishes Protopterus aethiopicus and Protopterus annectens exposed to terrestrial conditions for six days
Journal of Experimental Zoology Part A: Comparative Experimental Biology, 2005Co-Authors: Ai M Loong, Shit F Chew, Kum C Hiong, Wai Peng Wong, Yuen K IpAbstract:The objectives of this study were (1) to determine the type of carbamoyl phosphate synthetase (CPS) present, and the compartmentalization of arginase, in the livers of the African lungfishes, Protopterus aethiopicus and Protopterus annectens, and (2) to elucidate if these two lungfishes were capable of increasing the rates of urea synthesis and capacities of the ornithine-urea cycle (OUC) during 6 days of aerial exposure without undergoing aestivation. Like another African lungfish, Protopterus dolloi, reported elsewhere, the CPS activities from the livers of P. aethiopicus and P. annectens had properties similar to that of the marine ray (Taeniura lymma), but dissimilar to that of the mouse (Mus musculus). Hence, they possessed CPS III, and not CPS I as reported previously. CPS III was present exclusively in the liver mitochondria of both lungfishes, but the majority of the arginase activities were present in the cytosolic fractions of their livers. Glutamine synthetase (GS) activity was also detected in the hepatic mitochondria of both specimens. Therefore, our results suggest that the evolution of CPS III to CPS I might not have occurred before the evolution of extant lungfishes as suggested previously, prompting an examination of the current view on the evolution of CPS and OUC in vertebrates. Aerial exposure led to significant decreases in rates of ammonia excretion in P. aethiopicus and P. annectens, but there were no accumulations of ammonia in their tissues. However, urea contents in their tissues increased significantly after 6 days of aerial exposure. The estimated rates of urea synthesis in P. aethiopicus and P. annectens increased 1.2- and 1.47-fold, respectively, which were smaller than that in P. dolloi (8.6-fold) reported elsewhere. In addition, unlike P. dolloi, 6 days of aerial exposure had no significant effects on the hepatic CPS III activities of P. aethiopicus and P. annectens. In contrast, aerial exposure induced relatively greater degrees of reductions in ammonia production in P. aethiopicus (34%) and P. annectens (37%) than P. dolloi (28%) as previously reported. Thus, our results suggest that various species of African lungfishes respond to aerial exposure differently with respect to nitrogen metabolism and excretion, and it can be concluded that P. aethiopicus and P. annectens depended more on reductions in ammonia production than on increases in urea synthesis to ameliorate ammonia toxicity when exposed to terrestrial conditions. J. Exp. Zool. 303A:354–365, 2005. © 2005 Wiley-Liss, Inc.
Lauren J Chapman - One of the best experts on this subject based on the ideXlab platform.
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respiratory allocation and standard rate of metabolism in the african lungfish Protopterus aethiopicus
Comparative Biochemistry and Physiology A-molecular & Integrative Physiology, 2006Co-Authors: Ashley W Seifert, Lauren J ChapmanAbstract:This paper quantifies the relationship between respiratory allocation (air vs. water) and the standard rate of metabolism (SMR) in the primitive air-breathing lungfish, Protopterus aethiopicus. Simultaneous measurements of oxygen consumed from both air and water were made to determine the SMR at ecologically relevant aquatic oxygen levels for juveniles 2 to 221 g. Total metabolic rate was positively correlated with body mass with a scaling exponent of 0.78. Aerial oxygen consumption averaged 98% (range=94% to 100%) of total respiratory allocation under low aquatic oxygen levels. Measurements of oxygen consumption made across a gradient of dissolved oxygen from normoxia to anoxia showed that P. aethiopicus maintains its SMR despite a change in respiratory allocation between water and air.
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decline of the african lungfish Protopterus aethiopicus in lake victoria east africa
African Journal of Ecology, 2002Co-Authors: K P Goudswaard, Frans Witte, Lauren J ChapmanAbstract:Catch and effort data for the period 1973–1990 demonstrate a dramatic decline of lungfish in the Tanzanian waters of Lake Victoria. Bottom trawl catches in the Mwanza Gulf showed a decline in catch rates from 67.5 kg h−1 in 1973 to 5.5 kg h−1 in 1986. Trawling of commercial vessels in the Speke Gulf revealed a decline in lungfish catches from 1.3 kg h−1 in 1986 to 0.07 kg h−1 in 1990. The development of anoxia in the deeper waters of Lake Victoria, the algal blooms, and the decline of water transparency, all associated with eutrophication, are not likely to have contributed to the decreased catch rate. However, the lungfish decline may reflect the interaction of overexploitation by the fishery and a low level of Nile perch predation that restricts lungfish to wetland refugia. We suggest that this may have been reinforced over the past few decades by large-scale conversion of wetlands to agricultural land and harvesting of nest-guarding male lungfish leading to decreased recruitment of young. Resume Les donnees sur les prises et les efforts de capture pour la periode qui va de 1973 a 1990 montrent un declin spectaculaire des protopteres dans les eaux tanzaniennes du lac Victoria. Les prises faites au chalut dans le golfe de Mwanza montraient une reduction des taux de prises de 67,5 kg/h en 1973 a 5,5 kg/h en 1986. Les bateaux commerciaux qui pechent au chalut dans le golfe de Speke ont rapporte un declin de leurs prises de protopteres de 1,3 kg/h en 1986 a 0,07 kg/h en 1990. L'extension de l'anoxie dans les eaux profondes du lac Victoria, la profusion d'algues et la diminution de la transparence de l'eau, qui sont toutes associees a l'eutrophisation, sont peu susceptibles d'avoir contribue au declin du taux de prises. Le declin des protopteres peut cependant refleter l'interaction entre la surexploitation par la peche et un faible taux de predation de la perche du Nil qui repousse les protopteres vers les refuges marecageux. On suggere que ce phenomene a peut-etre ete renforce ces dernieres decennies par la transformation a grande echelle de terrains marecageux en terres agricoles et par le fait que les prelevements de protopteres mâles qui gardent les nids ont entraine une reduction du nombre de jeunes qui grandissent.
Chrisestom M Mlewa - One of the best experts on this subject based on the ideXlab platform.
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genetic variation in the marbled lungfish Protopterus aethiopicus in lake victoria and introduction to lake baringo kenya
Journal of Fish Biology, 2006Co-Authors: Shawn R. Garner, T P Birt, Ashley W Seifert, Chrisestom M Mlewa, John M. Green, V L FriesenAbstract:Marbled lungfish Protopterus aethiopicus in Lake Victoria and two nearby smaller lakes were found to have high levels of DNA sequence variation in their mitochondrial control regions (35 haplotypes in 61 fish) but no population genetic structure (Φ ST = 0·00). In contrast, marbled lungfish in Lake Baringo, Kenya, appeared to be fixed for a single control region haplotype, which occurred at low frequency in the other lakes. Using FLUCTUATE software, the female effective population size in Lake Victoria during the late Pleistocene was estimated to be c. 500 000, similar to the value estimated for the present-day population. These observations suggest that, during the late Pleistocene dry period, a large marbled lungfish population survived either in wet refugial areas within the lake basin or in surrounding areas. Marbled lungfish were reported to have been introduced into Lake Baringo 30 years ago with a founding population of only three individuals. The lack of control region variation in the Lake Baringo population is consistent with that situation.
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translocation of marbled african lungfish Protopterus aethiopicus telostei protopteridae and its fishery in lake baringo kenya
African Journal of Aquatic Science, 2006Co-Authors: Chrisestom M Mlewa, John M. GreenAbstract:The translocation of the marbled African lungfish Protopterus aethiopicus into Lake Baringo created a new fishery for the local community, who capture them primarily in a bottom-set long line fishery. Its introduction, development and current fishery status in the lake are documented. Annual catch data were obtained from the District Fisheries Office, while catch and effort data of the long line fishery were recorded at one active fish-landing site between February and October 2001. Lungfish comprise a significant component of commercial landings, sometimes exceeding catches of the Baringo tilapia Oreochromis niloticus baringoensis as the most landed species by weight. Daily catch rates and effort varied considerably, ranging from 5.51–15.18kg day−1 and from 50–590 baited hooks day−1, respectively. Daily catch per fisher ranged from 0–35.72kg, while the overall mean catch per unit effort (CPUE) was only 0.003kg per hook-hour. This study provides the only baseline CPUE data for a lungfish long line fishery...
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movement and habitat use by the marbled lungfish Protopterus aethiopicus heckel 1851 in lake baringo kenya
Hydrobiologia, 2005Co-Authors: Chrisestom M Mlewa, John M. Green, Alvin SimmsAbstract:The marbled lungfish, Protopterus aethiopicus, a recent introduction into Lake Baringo, Kenya is now an important commercial species there. Because little is known about its behaviour, we used ultrasonic telemetry to investigate its movements and use of habitat as part of a broader biological study. Twelve marbled lungfish were implanted with ultrasonic tags and tracked for variable periods between September 2001 and 2002. Two individuals were tracked for most of the study period. Daily movement ranged from little or none to 5.2 km. Mean hourly rates of movement for three fish located twice a day (morning and late afternoon) over several days suggested that individuals were active throughout the diel period. Maximum lake depth was about 3 m and fish utilized all depths greater than 1 m. Six home ranges described for four lungfish varied in size from 5.8 to 19.8 km 2 and were occupied for between 2 and 4.5 months. Use of habitat and the movement of marbled lungfish in Lake Baringo appeared to be influenced more by biotic than abiotic factors.
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biology of the marbled lungfish Protopterus aethiopicus heckel in lake baringo kenya
African Journal of Ecology, 2004Co-Authors: Chrisestom M Mlewa, John M. GreenAbstract:In this paper we provide life history characteristics for an introduced marbled lungfish (Protopterus aethiopicus) population in Lake Baringo, Kenya, including their length–weight relationship, body condition, fecundity, sex ratio, reproduction and food. These data are compared with those of other populations. Samples were obtained from the commercial fishery between January and October 2001. The lungfish exhibited positive allometric growth, with the length–weight relationship described by the equation: logW = −6.41 + 3.52 logTL. The mean relative condition factor was close to unity, did not vary much between months and was not significantly different between sexes. The overall sex ratio was skewed in favour of females. The size of fish at first maturity was 70–76 cm total length (TL) for females and 82–88 cm TL for males. Fish in maturity stages III–IV occurred in all monthly samples suggesting year round spawning. The marbled lungfish in Lake Baringo is largely piscivorous and its impact on other fishes certainly warrants further research. Resume Dans cet article, nous donnons les caracteristiques de l'historique d'une population de poissons (Protopterus aethiopicus) introduits dans le lac Baringo, au Kenya, y compris la relation longueur/poids, la condition physique, la fecondite, le sex-ratio, la reproduction et la nourriture. On compare ces donnees avec celles d'autres populations. Nous avons obtenu des echantillons aupres des pecheries entre janvier et octobre 2001. Le protoptere presente une croissance allometrique positive, avec la relation longueur–poids qui se decrit par l’equation: log W = −6,41 + 3,52 logLT. Le facteur moyen de condition relative etait proche de l'unite, ne variait pas beaucoup entre les mois et n’etait pas significativement different entre les sexes. Le sex-ratio global penchait en faveur des femelles. La taille des poissons au debut de la maturiteetait de 70–76 cm de longueur totale (LT) pour les femelles et de 82–88 cm LT pour les mâles. On trouvait des poissons aux stades de maturite III–IV dans tous les echantillons mensuels, ce qui suggere un frai qui dure toute l'annee. Ce protoptere du lac Baringo est largement piscivore, et son impact sur les autres especes de poissons merite certainement de plus amples recherches.
Alvin Simms - One of the best experts on this subject based on the ideXlab platform.
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movement and habitat use by the marbled lungfish Protopterus aethiopicus heckel 1851 in lake baringo kenya
Hydrobiologia, 2005Co-Authors: Chrisestom M Mlewa, John M. Green, Alvin SimmsAbstract:The marbled lungfish, Protopterus aethiopicus, a recent introduction into Lake Baringo, Kenya is now an important commercial species there. Because little is known about its behaviour, we used ultrasonic telemetry to investigate its movements and use of habitat as part of a broader biological study. Twelve marbled lungfish were implanted with ultrasonic tags and tracked for variable periods between September 2001 and 2002. Two individuals were tracked for most of the study period. Daily movement ranged from little or none to 5.2 km. Mean hourly rates of movement for three fish located twice a day (morning and late afternoon) over several days suggested that individuals were active throughout the diel period. Maximum lake depth was about 3 m and fish utilized all depths greater than 1 m. Six home ranges described for four lungfish varied in size from 5.8 to 19.8 km 2 and were occupied for between 2 and 4.5 months. Use of habitat and the movement of marbled lungfish in Lake Baringo appeared to be influenced more by biotic than abiotic factors.
Ai M Loong - One of the best experts on this subject based on the ideXlab platform.
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defense against environmental ammonia toxicity in the african lungfish Protopterus aethiopicus bimodal breathing skin ammonia permeability and urea synthesis
Aquatic Toxicology, 2007Co-Authors: Ai M Loong, Shit F Chew, Wai P Wong, Yuen K IpAbstract:Abstract This study aimed to determine how the African lungfish Protopterus aethiopicus defended against ammonia toxicity when confronted with high concentrations (30 or 100 mmol l −1 ) of environmental ammonia . Exposure to 100 mmol l −1 of NH 4 Cl for 1 or 6 days had no significant effect on the rate of O 2 uptake from water or from air, and the rate of total O 2 consumption. Using an Ussing-like apparatus, we report for the first time that the skin of P. aethiopicus had low permeability (1.26 × 10 −4 μmol min −1 cm −1 ) to NH 3 in vitro . Indeed, the influx of exogenous ammonia into fish exposed to 30 mmol l −1 NH 4 Cl was low (0.117 μmol min −1 100 g −1 fish). As a result, P. aethiopicus could afford to maintain relatively low ammonia contents in plasma, muscle, liver and brain even after 6 days of exposure to 100 mmol l −1 NH 4 Cl. Surprisingly, fish exposed to 30 or 100 mmol l −1 NH 4 Cl had comparable ammonia contents in the muscle and the brain in spite of the big difference (70 mmol l −1 ) in environmental ammonia concentrations. Significant increases in urea contents occurred in various tissues of fish exposed to 30 mmol l −1 NH 4 Cl for 6 days, but there were no significant differences in tissue urea contents between fish exposed to 30 mmol l −1 and 100 mmol l −1 NH 4 Cl. Between days 3 and 6, the rate of urea excretion in fish exposed to 30 mmol l −1 NH 4 Cl was significantly greater than that of the control. By contrast, there was no significant difference in urea excretion rates between fish exposed to 100 mmol l −1 NH 4 Cl and control fish throughout the 6-day period, and such a phenomenon has not been reported before for other lungfish species. Thus, our results suggest that P. aethiopicus was capable of decreasing the NH 3 permeability of its body surface when exposed to high concentrations of environmental ammonia. Indeed, after 6 days of exposure to 100 mmol l −1 NH 4 Cl, the NH 3 permeability constant of the skin (0.55 × 10 −4 μmol min −1 cm −1 ) decreased to half of that of the control. A decrease in the already low cutaneous NH 3 permeability and an increased urea synthesis, working in combination, allowed P. aethiopicus to effectively defend against environmental ammonia toxicity without elevating the plasma ammonia level. Therefore, unlike other fishes, glutamine and alanine contents did not increase in the muscle and liver, and there was no accumulation of glutamine in the brain, even when the fish was immersed in water containing 100 mmol l −1 NH 4 Cl.
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the interplay of increased urea synthesis and reduced ammonia production in the african lungfish Protopterus aethiopicus during 46 days of aestivation in a mucus cocoon
Journal of Experimental Zoology Part A: Comparative Experimental Biology, 2005Co-Authors: Yuen K Ip, Ai M Loong, Kum C Hiong, Wai Peng Wong, Shit F ChewAbstract:This study was undertaken to test the hypothesis that the rate of urea synthesis in Protopterus aethiopicus was up-regulated to detoxify ammonia during the initial phase of aestivation in air (day 1–day 12), and that a profound suppression of ammonia production occurred at a later phase of aestivation (day 35–day 46) which eliminated the need to sustain the increased rate of urea synthesis. Fasting apparently led to a greater rate of nitrogenous waste excretion in P. aethiopicus in water, which is an indication of increases in production of endogenous ammonia and urea probably as a result of increased proteolysis and amino acid catabolism for energy production. However, 46 days of fasting had no significant effects on the ammonia or urea contents in the muscle, liver, plasma and brain. In contrast, there were significant decreases in the muscle ammonia content in fish after 12, 34 or 46 days of aestivation in air when compared with fish fasting in water. Ammonia was apparently detoxified to urea because urea contents in the muscle, liver, plasma and brain of P. aethiopicus aestivated for 12, 34 or 46 days were significantly greater than the corresponding fasting control; the greatest increases in urea contents occurred during the initial 12 days. There were also significant increases in activities of some of the hepatic ornithine–urea cycle enzymes from fish aestivated for 12 or 46 days. Therefore, contrary to a previous report on P. aethiopicus, our results demonstrated an increase in the estimated rate of urea synthesis (2.8-fold greater than the day 0 fish) in this lungfish during the initial 12 days of aestivation. However, the estimated rate of urea synthesis decreased significantly during the next 34 days. Between day 35 and day 46 (12 days), urea synthesis apparently decreased to 42% of the day 0 control value, and this is the first report of such a phenomenon in African lungfish undergoing aestivation. On the other hand, the estimated rate of ammonia production in P. aethiopicus increased slightly (14.7%) during the initial 12 days of aestivation as compared with that in the day 0 fish. By contrast, the estimated rate of ammonia production decreased by 84% during the final 12 days of aestivation (day 35–day 46) compared with the day 0 value. Therefore, it can be concluded that P. aethiopicus depended mainly on increased urea synthesis to ameliorate ammonia toxicity during the initial phase of aestivation, but during prolonged aestivation, it suppressed ammonia production profoundly, eliminating the need to increase urea synthesis which is energy-intensive. J. Exp. Zool. 303A:1054–1065, 2005. © 2005 Wiley-Liss, Inc.
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ornithine urea cycle and urea synthesis in african lungfishes Protopterus aethiopicus and Protopterus annectens exposed to terrestrial conditions for six days
Journal of Experimental Zoology Part A: Comparative Experimental Biology, 2005Co-Authors: Ai M Loong, Shit F Chew, Kum C Hiong, Wai Peng Wong, Yuen K IpAbstract:The objectives of this study were (1) to determine the type of carbamoyl phosphate synthetase (CPS) present, and the compartmentalization of arginase, in the livers of the African lungfishes, Protopterus aethiopicus and Protopterus annectens, and (2) to elucidate if these two lungfishes were capable of increasing the rates of urea synthesis and capacities of the ornithine-urea cycle (OUC) during 6 days of aerial exposure without undergoing aestivation. Like another African lungfish, Protopterus dolloi, reported elsewhere, the CPS activities from the livers of P. aethiopicus and P. annectens had properties similar to that of the marine ray (Taeniura lymma), but dissimilar to that of the mouse (Mus musculus). Hence, they possessed CPS III, and not CPS I as reported previously. CPS III was present exclusively in the liver mitochondria of both lungfishes, but the majority of the arginase activities were present in the cytosolic fractions of their livers. Glutamine synthetase (GS) activity was also detected in the hepatic mitochondria of both specimens. Therefore, our results suggest that the evolution of CPS III to CPS I might not have occurred before the evolution of extant lungfishes as suggested previously, prompting an examination of the current view on the evolution of CPS and OUC in vertebrates. Aerial exposure led to significant decreases in rates of ammonia excretion in P. aethiopicus and P. annectens, but there were no accumulations of ammonia in their tissues. However, urea contents in their tissues increased significantly after 6 days of aerial exposure. The estimated rates of urea synthesis in P. aethiopicus and P. annectens increased 1.2- and 1.47-fold, respectively, which were smaller than that in P. dolloi (8.6-fold) reported elsewhere. In addition, unlike P. dolloi, 6 days of aerial exposure had no significant effects on the hepatic CPS III activities of P. aethiopicus and P. annectens. In contrast, aerial exposure induced relatively greater degrees of reductions in ammonia production in P. aethiopicus (34%) and P. annectens (37%) than P. dolloi (28%) as previously reported. Thus, our results suggest that various species of African lungfishes respond to aerial exposure differently with respect to nitrogen metabolism and excretion, and it can be concluded that P. aethiopicus and P. annectens depended more on reductions in ammonia production than on increases in urea synthesis to ameliorate ammonia toxicity when exposed to terrestrial conditions. J. Exp. Zool. 303A:354–365, 2005. © 2005 Wiley-Liss, Inc.
