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Chris M Wood - One of the best experts on this subject based on the ideXlab platform.
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rh proteins and nh4 activated na atpase in the magadi tilapia alcolapia grahami a 100 ureotelic teleost fish
The Journal of Experimental Biology, 2013Co-Authors: Chris M Wood, Pierre Laurent, Claudine Chevalier, Harold L. Bergman, Jonathan M Wilson, Adalto Bianchini, John N Maina, Michele C Nawata, Ora E JohannssonAbstract:SUMMARY The small cichlid fish Alcolapia grahami lives in Lake Magadi, Kenya, one of the most extreme aquatic environments on Earth (pH ~10, carbonate alkalinity ~300 mequiv l −1 ). The Magadi tilapia is the only 100% ureotelic teleost; it normally excretes no ammonia. This is interpreted as an evolutionary adaptation to overcome the near impossibility of sustaining an NH 3 diffusion gradient across the gills against the high external pH. In standard ammoniotelic teleosts, branchial ammonia excretion is facilitated by Rh glycoproteins, and cortisol plays a role in upregulating these carriers, together with other components of a transport metabolon, so as to actively excrete ammonia during high environmental ammonia (HEA) exposure. In Magadi tilapia, we show that at least three Rh proteins ( Rhag , Rhbg and Rhcg2 ) are expressed at the mRNA level in various tissues, and are recognized in the gills by specific antibodies. During HEA exposure, plasma ammonia levels and urea excretion rates increase markedly, and mRNA expression for the branchial urea transporter mtUT is elevated. Plasma cortisol increases and branchial mRNAs for Rhbg , Rhcg2 and Na + ,K + -ATPase are all upregulated. Enzymatic activity of the latter is activated preferentially by NH 4 + ( versus K + ), suggesting it can function as an NH 4 + -transporter. Model calculations suggest that active ammonia excretion against the gradient may become possible through a combination of Rh protein and NH 4 + -activated Na + -ATPase function.
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increased gene expression of a facilitated diffusion urea transporter in the skin of the african lungfish protopterus annectens during massively elevated post terrestrialization urea excretion
The Journal of Experimental Biology, 2009Co-Authors: Carrie Y C Hung, Fernando Galvez, Yuen K Ip, Chris M WoodAbstract:The full-length cDNA sequence of a putative urea transporter ( lfUT ) of the facilitated diffusion UT-A type has been cloned from the African lungfish Protopterus annectens . The lfUT cDNA is 1990 bp in length and its open reading frame encodes a 409 amino acid long protein, with a calculated molecular mass of 44,723 Da. The sequence is closest to those of amphibians (∼65% amino acid homology), followed by mammals and elasmobranchs (∼60%), and then teleosts (∼50%). lfUT was clearly expressed in gill, kidney, liver, skeletal muscle and skin. Upon re-immersion in water after 33 days of air exposure (`terrestrialization'), lungfish exhibited a massive rise in urea-N excretion which peaked at 12–30 h with rates of 2000–5000 μmol-N kg–1 h–1 (versus normal aquatic rates of<130 μmol-N kg–1 h–1) and persisted until 70 h. This appears to occur mainly through the skin. Total `excess' urea-N excretion amounted to ∼81,000–91,000 μmol-N kg–1 over 3 days. By real-time PCR, there was no difference in lfUT expression in the ventral abdominal skin between aquatic ammoniotelic controls and terrestrialized lungfish immediately after return to water (0 h), and no elevation of urea-N excretion at this time. However, skin biopsies revealed a significant 2.55-fold elevation of lfUT expression at 14 h, coincident with peak urea-N excretion. At 48 h, there was no longer any significant difference in lfUT mRNA levels from those at 0 and 14 h, or from aquatic fed controls. In accordance with earlier studies, which identified elevated urea-N excretion via the skin of P. dolloi with pharmacology typical of UT-A carriers, these results argue that transcriptional activation of a facilitated diffusion type urea transporter ( lfUT ) occurs in the skin during re-immersion. This serves to clear the body burden of urea-N accumulated during terrestrialization.
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increased gene expression of a facilitated diffusion urea transporter in the skin of the african lungfish protopterus annectens during massively elevated post terrestrialization urea excretion
The Journal of Experimental Biology, 2009Co-Authors: Carrie Y C Hung, Fernando Galvez, Chris M WoodAbstract:The full-length cDNA sequence of a putative urea transporter (lfUT) of the facilitated diffusion UT-A type has been cloned from the African lungfish Protopterus annectens. The lfUT cDNA is 1990 bp in length and its open reading frame encodes a 409 amino acid long protein, with a calculated molecular mass of 44,723 Da. The sequence is closest to those of amphibians ( approximately 65% amino acid homology), followed by mammals and elasmobranchs ( approximately 60%), and then teleosts ( approximately 50%). lfUT was clearly expressed in gill, kidney, liver, skeletal muscle and skin. Upon re-immersion in water after 33 days of air exposure ('terrestrialization'), lungfish exhibited a massive rise in urea-N excretion which peaked at 12-30 h with rates of 2000-5000 micromol-N kg(-1) h(-1) (versus normal aquatic rates of <130 micromol-N kg(-1) h(-1)) and persisted until 70 h. This appears to occur mainly through the skin. Total 'excess' urea-N excretion amounted to approximately 81,000-91,000 micromol-N kg(-1) over 3 days. By real-time PCR, there was no difference in lfUT expression in the ventral abdominal skin between aquatic ammoniotelic controls and terrestrialized lungfish immediately after return to water (0 h), and no elevation of urea-N excretion at this time. However, skin biopsies revealed a significant 2.55-fold elevation of lfUT expression at 14 h, coincident with peak urea-N excretion. At 48 h, there was no longer any significant difference in lfUT mRNA levels from those at 0 and 14 h, or from aquatic fed controls. In accordance with earlier studies, which identified elevated urea-N excretion via the skin of P. dolloi with pharmacology typical of UT-A carriers, these results argue that transcriptional activation of a facilitated diffusion type urea transporter (lfUT) occurs in the skin during re-immersion. This serves to clear the body burden of urea-N accumulated during terrestrialization.
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greatly elevated urea excretion after air exposure appears to be carrier mediated in the slender lungfish protopterus dolloi
Physiological and Biochemical Zoology, 2005Co-Authors: Chris M Wood, Patrick J Walsh, Shit F. Chew, Yuen K IpAbstract:Abstract Under aquatic conditions, Protopterus dolloi is ammoniotelic, excreting only small amounts of urea‐N. However, upon return to water after 30 d estivation in air, the lungfish excretes only small amounts of ammonia‐N but massive amounts of urea‐N. A similar pattern is seen after 21–30 d of terrestrialization, a treatment in which the lungfish is air exposed but kept moist throughout. After both treatments, the time course of urea‐N excretion is biphasic with an immediate increase, then a fall, and finally a second larger increase that peaks at about 12 h and may be prolonged for several days thereafter. Urea‐N excretion rates during the second peak reach 2,000–6,000 μmol N kg−1 h−1, two to three orders of magnitude greater than rates in most fish and comparable only to rates in species known to employ UT‐A type facilitated diffusion urea transporters. Divided chamber studies and measurements of the clearance rates of [3H]‐PEG‐4000 (a glomerular filtration and paracellular diffusion marker) and two...
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evidence for facilitated diffusion of urea across the gill basolateral membrane of the rainbow trout oncorhynchus mykiss
Biochimica et Biophysica Acta, 2004Co-Authors: Danielle M Mcdonald, Chris M WoodAbstract:Recent in vivo evidence suggests that the mechanism of branchial urea excretion in the ammoniotelic rainbow trout (Oncorhynchus mykiss) is carrier-mediated. Further characterization of this proposed mechanism was achieved by using an in vitro isolated basolateral membrane vesicle (BLMV) preparation in which isolated gill membranes were used to determine a variety of physiological properties of the transporter. BLMV demonstrated two components of urea uptake, a linear component at concentrations up to 17.5 mmol x l(-1) and a saturable component (K(0.5)=0.35+/-0.01 mmol x l(-1); V(max)=0.14+/-0.02 micromol mg protein(-1) h(-1)) with a Hill constant of 1.35+/-0.18 at low, physiologically relevant urea concentrations ( 2 suggesting a protein carrier-mediated process. Combined, this evidence indicates that a facilitated diffusion urea transport mechanism is likely present in the basolateral membrane of the rainbow trout gill.
Paul M Anderson - One of the best experts on this subject based on the ideXlab platform.
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nitrogen excretion and expression of carbamoyl phosphate synthetase iii activity and mrna in extrahepatic tissues of largemouth bass micropterus salmoides
Archives of Biochemistry and Biophysics, 1998Co-Authors: Haiyan Kong, Joseph J Korte, Wilmar L Salo, Patricia A Wright, Dale D Edberg, Paul M AndersonAbstract:Low levels of all of the enzymes required for urea synthesis via the urea cycle, including mitochondrial glutamine- and acetylglutamate-dependent carbamoyl-phosphate synthetase III (CPSase III) and cytosolic glutamine synthetase, are known to be present in liver of the teleost fish largemouth bass (Micropterus salmoides). The levels of these enzymes are higher than those in most other teleosts, but they are significantly lower than the levels present in liver of ureoosmotic elasmobranchs. The purpose of this study was to assess the physiological role of CPSase III in the context of urea synthesis in adult bass. The results showed that urea–N accounts for about 30% of the total nitrogen (ammonia–N plus urea–N) excreted under control conditions. The rate of urea–N excretion did not increase in response to exposure to 1 mM NH4Cl (3 days) or 0.25 mM NH4Cl (12 days) in the external water, except for a transient increase after a day or two of exposure. CPSase III activity in liver also did not increase in response to exposure to ammonia. Adult largemouth bass, while apparently ureogenic, are primarily Ammonotelic and remain so even in the presence of relatively high concentrations of ammonia in the external environment. The total units of CPSase III activity in liver are not sufficient to account for the quantity of urea that is excreted. However, CPSase III and ornithine carbamoyltransferase (OCTase) activities were found to be present in intestinal tissue and, unexpectedly, in muscle tissue. The total units of CPSase III and OCTase in muscle, intestine, and liver appear to be sufficient to account for the observed rate of urea excretion. The sequence of CPSase III cDNA was determined, which permitted the use of ribonuclease protection assays to demonstrate the presence of CPSase III mRNA in these tissues.
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expression of carbamoyl phosphate synthetase iii mrna during the early stages of development and in muscle of adult rainbow trout oncorhynchus mykiss
Journal of Biological Chemistry, 1997Co-Authors: Joseph J Korte, Wilmar L Salo, Vicente M Cabrera, Patricia A Wright, Andrew K Felskie, Paul M AndersonAbstract:It has been reported that the activities of the urea cycle-related enzymes ornithine carbamoyltransferase and carbamoyl-phosphate synthetase III (CPSase III) are induced during early life stages of Ammonotelic rainbow trout (Oncorhynchus mykiss), suggesting that the urea cycle may play a physiological role in early development in teleost fish (Wright, P. A., Felskie, A., and Anderson, P. M. (1995) J. Exp. Biol. 198, 127-135). CPSase III cDNA prepared from embryo mRNA was sequenced, confirming the existence of the CPSase III gene in trout and its expression. The deduced amino acid sequence of the CPSase III is homologous to other CPSases. Supporting evidence for the expression of CPSase III activity in trout embryos was obtained by demonstrating expression of CPSase III mRNA as early as day 3 post-fertilization, reaching a maximum at 10-14 days, declining to a minimum at day 70, and then increasing to a relatively constant level from days 90 to 110 (relative to total RNA). Unexpectedly, in tissues of adult and fingerling trout, CPSase III mRNA was found to be present in muscle but not in other tissues, including liver. This finding was confirmed by assay of extracts, which showed CPSase III and ornithine carbamoyltransferase activity in muscle but not in other tissues. The pyrimidine nucleotide pathway-related CPSase II mRNA was expressed in all tissues.
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induction of ornithine urea cycle enzymes and nitrogen metabolism and excretion in rainbow trout oncorhynchus mykiss during early life stages
The Journal of Experimental Biology, 1995Co-Authors: Patricia A Wright, A Felskie, Paul M AndersonAbstract:The ornithinesurea cycle (OUC) is present in elasmobranch fish and many terrestrial vertebrates. Recently, a functional OUC has been reported in a few teleost species, suggesting that all teleost fish have the genes for the OUC, but expression is relatively rare. We investigated the possibility that the OUC is expressed during early development in trout as a mechanism for detoxifying ammonia produced from the catabolism of yolk protein. We followed ammonia and urea excretion rates, tissue ammonia and urea levels and OUC enzyme activities in rainbow trout up to 93 days after fertilization. Both ammonia and urea tissue concentrations increased several-fold in the first 40 days after fertilization (embryo stage), peaking at 1.7 mmol N l-1 and 2.5 mmol N l-1, respectively. Ammonia excretion could be detected in 4-day-old embryos, but urea excretion was not initiated until after hatching (day 45). Urea excretion in larval fish (days 42s93) increased several-fold and by day 93 was 14 % of total nitrogen excretion, as found in adult trout. Glutamine synthetase (GSase) and arginase activities were detected in 9whole animal9 homogenates just after hatching and the levels of activity increased markedly to day 93. Carbamoyl phosphate synthetase (CPSase) and ornithine transcarbamylase (OTCase) were first detected in 40-day-old embryos; activities peaked between days 53 and 71 and then subsequently decreased. Adult liver enzyme activity for GSase was several-fold lower than in whole larval trout and OTCase and CPSase III (glutamine- and N-acetylglutamate-dependent CPSase catalysing the first step of the OUC) activities were essentially absent in adult liver. We conclude that embryonic and larval trout are primarily ammoniotelic. Urea is synthesized immediately after fertilization, but is not excreted until after the embryo is hatched. The results provide evidence for the presence of the OUC in larval rainbow trout, since four of the OUC enzymes are induced just after hatching and the levels of activity are relatively high compared with those in adult liver tissue. Furthermore, we suggest that all teleosts have retained the OUC genes, which are expressed only during certain stages of development (embryogenesis), and in a few rare species expression is maintained throughout the life cycle to cope with unusual environmental conditions (e.g. alkaline water, air exposure).
Yuen K Ip - One of the best experts on this subject based on the ideXlab platform.
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molecular characterization of three rhesus glycoproteins from the gills of the african lungfish protopterus annectens and effects of aestivation on their mrna expression levels and protein abundance
PLOS ONE, 2017Co-Authors: You R. Chng, Biyun Ching, Xiu L. Chen, Kum C. Hiong, Wai P. Wong, Shit F. Chew, Yuen K IpAbstract:: African lungfishes are Ammonotelic in water. They can aestivate for long periods on land during drought. During aestivation, the gills are covered with dried mucus and ammonia excretion ceases. In fishes, ammonia excretion through the gills involves Rhesus glycoproteins (RhGP/Rhgp). This study aimed to obtain the complete cDNA coding sequences of rhgp from the gills of Protopterus annectens, and to determine their branchial mRNA and protein expression levels during the induction, maintenance and arousal phases of aestivation. Three isoforms of rhgp (rhag, rhbg and rhcg) were obtained in the gills of P. annectens. Their complete cDNA coding sequences ranged between 1311 and 1398 bp, coding for 436 to 465 amino acids with estimated molecular masses between 46.8 and 50.9 kDa. Dendrogramic analyses indicated that Rhag was grouped closer to fishes, while Rhbg and Rhcg were grouped closer to tetrapods. During the induction phase, the protein abundance of Rhag, but not its transcript level, was down-regulated in the gills, suggesting that there could be a decrease in the release of ammonia from the erythrocytes to the plasma. Furthermore, the branchial transcript levels of rhbg and rhcg decreased significantly, in preparation for the subsequent shutdown of gill functions. During the maintenance phase, the branchial expression levels of rhag/Rhag, rhbg/Rhbg and rhcg/Rhcg decreased significantly, indicating that their transcription and translation were down-regulated. This could be part of an overall mechanism to shut down branchial functions and save metabolic energy used for transcription and translation. It could also be regarded as an adaptive response to stop ammonia excretion. During the arousal phase, it is essential for the lungfish to regain the ability to excrete ammonia. Indeed, the protein abundance of Rhag, Rhbg and Rhcg recovered to the corresponding control levels after 1 day or 3 days of recovery from 6 months of aestivation.
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increased gene expression of a facilitated diffusion urea transporter in the skin of the african lungfish protopterus annectens during massively elevated post terrestrialization urea excretion
The Journal of Experimental Biology, 2009Co-Authors: Carrie Y C Hung, Fernando Galvez, Yuen K Ip, Chris M WoodAbstract:The full-length cDNA sequence of a putative urea transporter ( lfUT ) of the facilitated diffusion UT-A type has been cloned from the African lungfish Protopterus annectens . The lfUT cDNA is 1990 bp in length and its open reading frame encodes a 409 amino acid long protein, with a calculated molecular mass of 44,723 Da. The sequence is closest to those of amphibians (∼65% amino acid homology), followed by mammals and elasmobranchs (∼60%), and then teleosts (∼50%). lfUT was clearly expressed in gill, kidney, liver, skeletal muscle and skin. Upon re-immersion in water after 33 days of air exposure (`terrestrialization'), lungfish exhibited a massive rise in urea-N excretion which peaked at 12–30 h with rates of 2000–5000 μmol-N kg–1 h–1 (versus normal aquatic rates of<130 μmol-N kg–1 h–1) and persisted until 70 h. This appears to occur mainly through the skin. Total `excess' urea-N excretion amounted to ∼81,000–91,000 μmol-N kg–1 over 3 days. By real-time PCR, there was no difference in lfUT expression in the ventral abdominal skin between aquatic ammoniotelic controls and terrestrialized lungfish immediately after return to water (0 h), and no elevation of urea-N excretion at this time. However, skin biopsies revealed a significant 2.55-fold elevation of lfUT expression at 14 h, coincident with peak urea-N excretion. At 48 h, there was no longer any significant difference in lfUT mRNA levels from those at 0 and 14 h, or from aquatic fed controls. In accordance with earlier studies, which identified elevated urea-N excretion via the skin of P. dolloi with pharmacology typical of UT-A carriers, these results argue that transcriptional activation of a facilitated diffusion type urea transporter ( lfUT ) occurs in the skin during re-immersion. This serves to clear the body burden of urea-N accumulated during terrestrialization.
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greatly elevated urea excretion after air exposure appears to be carrier mediated in the slender lungfish protopterus dolloi
Physiological and Biochemical Zoology, 2005Co-Authors: Chris M Wood, Patrick J Walsh, Shit F. Chew, Yuen K IpAbstract:Abstract Under aquatic conditions, Protopterus dolloi is ammoniotelic, excreting only small amounts of urea‐N. However, upon return to water after 30 d estivation in air, the lungfish excretes only small amounts of ammonia‐N but massive amounts of urea‐N. A similar pattern is seen after 21–30 d of terrestrialization, a treatment in which the lungfish is air exposed but kept moist throughout. After both treatments, the time course of urea‐N excretion is biphasic with an immediate increase, then a fall, and finally a second larger increase that peaks at about 12 h and may be prolonged for several days thereafter. Urea‐N excretion rates during the second peak reach 2,000–6,000 μmol N kg−1 h−1, two to three orders of magnitude greater than rates in most fish and comparable only to rates in species known to employ UT‐A type facilitated diffusion urea transporters. Divided chamber studies and measurements of the clearance rates of [3H]‐PEG‐4000 (a glomerular filtration and paracellular diffusion marker) and two...
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the Ammonotelic african lungfish protopterus dolloi increases the rate of urea synthesis and becomes ureotelic after feeding
Journal of Comparative Physiology B-biochemical Systemic and Environmental Physiology, 2004Co-Authors: Wai P. Wong, Shit F. Chew, Yuen K IpAbstract:This study aimed to elucidate the role of urea synthesis in the slender African lungfish Protopterus dolloi in detoxifying ammonia after feeding. There were significant increases in the rate of ammonia excretion in P. dolloi between hours 6 and 15 after feeding. Simultaneously, there were significant increases in urea excretion rates between hours 3 and 18. Consequently, the percentage of total nitrogen (N) excreted as urea N increased to ~60% between hours 12 and 21 post-feeding. Hence, after feeding, the normally Ammonotelic P. dolloi became ureotelic. Approximately 41% of the N intake from food was excreted within 24 h by P. dolloi, 55% of which was in the form of urea N. At hour 12 post-feeding, the accumulation of urea N was greater than the accumulation of ammonia N in various tissues, which indicates that feeding led to an increase in the rate of urea synthesis. This is contrary to results reported previously on the infusion of ammonia into the peritoneal cavity of the marine dogfish shark, in which a significant portion of the exogenous ammonia was excreted as ammonia. In contrast, feeding is more likely to induce urea synthesis, which is energy intensive, because feeding provides an ample supply of energy resources and leads to the production of ammonia intracellularly in the liver. The capacity of P. dolloi to synthesize urea effectively prevented a postprandial surge in the plasma ammonia level as reported elsewhere for other non-ureogenic teleosts. However, there was a significant increase in the glutamine content in the brain at hour 24, indicating that the brain had to defend against ammonia toxicity after feeding.
Shit F. Chew - One of the best experts on this subject based on the ideXlab platform.
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molecular characterization of three rhesus glycoproteins from the gills of the african lungfish protopterus annectens and effects of aestivation on their mrna expression levels and protein abundance
PLOS ONE, 2017Co-Authors: You R. Chng, Biyun Ching, Xiu L. Chen, Kum C. Hiong, Wai P. Wong, Shit F. Chew, Yuen K IpAbstract:: African lungfishes are Ammonotelic in water. They can aestivate for long periods on land during drought. During aestivation, the gills are covered with dried mucus and ammonia excretion ceases. In fishes, ammonia excretion through the gills involves Rhesus glycoproteins (RhGP/Rhgp). This study aimed to obtain the complete cDNA coding sequences of rhgp from the gills of Protopterus annectens, and to determine their branchial mRNA and protein expression levels during the induction, maintenance and arousal phases of aestivation. Three isoforms of rhgp (rhag, rhbg and rhcg) were obtained in the gills of P. annectens. Their complete cDNA coding sequences ranged between 1311 and 1398 bp, coding for 436 to 465 amino acids with estimated molecular masses between 46.8 and 50.9 kDa. Dendrogramic analyses indicated that Rhag was grouped closer to fishes, while Rhbg and Rhcg were grouped closer to tetrapods. During the induction phase, the protein abundance of Rhag, but not its transcript level, was down-regulated in the gills, suggesting that there could be a decrease in the release of ammonia from the erythrocytes to the plasma. Furthermore, the branchial transcript levels of rhbg and rhcg decreased significantly, in preparation for the subsequent shutdown of gill functions. During the maintenance phase, the branchial expression levels of rhag/Rhag, rhbg/Rhbg and rhcg/Rhcg decreased significantly, indicating that their transcription and translation were down-regulated. This could be part of an overall mechanism to shut down branchial functions and save metabolic energy used for transcription and translation. It could also be regarded as an adaptive response to stop ammonia excretion. During the arousal phase, it is essential for the lungfish to regain the ability to excrete ammonia. Indeed, the protein abundance of Rhag, Rhbg and Rhcg recovered to the corresponding control levels after 1 day or 3 days of recovery from 6 months of aestivation.
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aestivation induces changes in the mrna expression levels and protein abundance of two isoforms of urea transporters in the gills of the african lungfish protopterus annectens
Frontiers in Physiology, 2017Co-Authors: You R. Chng, Biyun Ching, Xiu L. Chen, Kum C. Hiong, Wai P. Wong, Shit F. Chew, Jasmine L Y Ong, Siew Hong LamAbstract:The African lungfish, Protopterus annectens, is Ammonotelic in water despite being ureogenic. When it aestivates in mucus cocoon on land, ammonia is detoxified to urea. During the maintenance phase of aestivation, urea accumulates in the body, which is subsequently excreted upon arousal. Urea excretion involves urea transporters (UT/Ut). This study aimed to clone and sequence the ut isoforms from the gills of P. annectens, and to test the hypothesis that the mRNA and/or protein expression levels of ut/Ut isoforms could vary in the gills of P. annectens during the induction, maintenance, and arousal phases of aestivation. Two isoforms of ut, ut-a2a and ut-a2b, were obtained from the gills of P. annectens. ut-a2a consists of 1227 bp and codes for 408 amino acids with an estimated molecular mass of 44.7 kDa, while ut-a2b consists of 1392 bp and codes for 464 amino acids with an estimated molecular mass of 51.2 kDa. Ut-a2a and Ut-a2b of P. annectens had a closer phylogenetic relationship with Ut/UT of tetrapods than Ut of fishes. While the mRNA expression pattern of ut-a2a and ut-a2b across various tissues of P. annectens differed, the transcript levels of ut-a2a and ut-a2b in the gills were comparable, indicating that they might be equally important for branchial urea excretion during the initial arousal phase of aestivation. During the maintenance phase of aestivation, the transcript level of ut-a2a increased significantly, but the protein abundance of Ut-a2a remained unchanged in P. annectens gills. This could be an adaptive feature to prepare for an increase in the production of Ut-a2a upon arousal. Indeed, arousal led to a significant increase in the branchial Ut-a2a protein abundance. Although the transcript level of ut-a2b remained unchanged, there were significant increases in the protein abundance of Ut-a2b in P. annectens gills throughout the three phases of aestivation. The increase in the protein abundance of Ut-a2b during the maintenance phase could also be an adaptive feature to prepare for efficient urea excretion when water becomes available.
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ammonia production excretion toxicity and defense in fish a review
Frontiers in Physiology, 2010Co-Authors: Shit F. ChewAbstract:Many fishes are Ammonotelic but some species can detoxify ammonia to glutamine or urea. Certain fish species can accumulate high levels of ammonia in the brain or defense against ammonia toxicity by enhancing the effectiveness of ammonia excretion through active NH4+ transport, manipulation of ambient pH, or reduction in ammonia permeability through the branchial and cutaneous epithelia. Recent reports on ammonia toxicity in mammalian brain reveal the importance of permeation of ammonia through the blood-brain barrier and passages of ammonia and water through transporters in the plasmalemma of brain cells. Additionally, brain ammonia toxicity could be related to the passage of glutamine through the mitochondrial membranes into the mitochondrial matrix. On the other hand, recent reports on ammonia excretion in fish confirm the involvement of Rhesus glycoproteins in the branchial and cutaneous epithelia. Therefore, this review focuses on both the earlier literature and the up-to-date information on the problems and mechanisms concerning the permeation of ammonia, as NH3, NH4+ or proton-neutral nitrogenous compounds, across mitochondrial membranes, the blood-brain barrier, the plasmalemma of neurons, and the branchial and cutaneous epithelia of fish. It also addresses how certain fishes with high ammonia tolerance defend against ammonia toxicity through the regulation of the permeation of ammonia and related nitrogenous compounds through various types of membranes. It is hoped that this review would revive the interests in investigations on the passage of ammonia through the mitochondrial membranes and the blood-brain barrier of Ammonotelic fishes and fishes with high brain ammonia-tolerance, respectively.
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greatly elevated urea excretion after air exposure appears to be carrier mediated in the slender lungfish protopterus dolloi
Physiological and Biochemical Zoology, 2005Co-Authors: Chris M Wood, Patrick J Walsh, Shit F. Chew, Yuen K IpAbstract:Abstract Under aquatic conditions, Protopterus dolloi is ammoniotelic, excreting only small amounts of urea‐N. However, upon return to water after 30 d estivation in air, the lungfish excretes only small amounts of ammonia‐N but massive amounts of urea‐N. A similar pattern is seen after 21–30 d of terrestrialization, a treatment in which the lungfish is air exposed but kept moist throughout. After both treatments, the time course of urea‐N excretion is biphasic with an immediate increase, then a fall, and finally a second larger increase that peaks at about 12 h and may be prolonged for several days thereafter. Urea‐N excretion rates during the second peak reach 2,000–6,000 μmol N kg−1 h−1, two to three orders of magnitude greater than rates in most fish and comparable only to rates in species known to employ UT‐A type facilitated diffusion urea transporters. Divided chamber studies and measurements of the clearance rates of [3H]‐PEG‐4000 (a glomerular filtration and paracellular diffusion marker) and two...
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the Ammonotelic african lungfish protopterus dolloi increases the rate of urea synthesis and becomes ureotelic after feeding
Journal of Comparative Physiology B-biochemical Systemic and Environmental Physiology, 2004Co-Authors: Wai P. Wong, Shit F. Chew, Yuen K IpAbstract:This study aimed to elucidate the role of urea synthesis in the slender African lungfish Protopterus dolloi in detoxifying ammonia after feeding. There were significant increases in the rate of ammonia excretion in P. dolloi between hours 6 and 15 after feeding. Simultaneously, there were significant increases in urea excretion rates between hours 3 and 18. Consequently, the percentage of total nitrogen (N) excreted as urea N increased to ~60% between hours 12 and 21 post-feeding. Hence, after feeding, the normally Ammonotelic P. dolloi became ureotelic. Approximately 41% of the N intake from food was excreted within 24 h by P. dolloi, 55% of which was in the form of urea N. At hour 12 post-feeding, the accumulation of urea N was greater than the accumulation of ammonia N in various tissues, which indicates that feeding led to an increase in the rate of urea synthesis. This is contrary to results reported previously on the infusion of ammonia into the peritoneal cavity of the marine dogfish shark, in which a significant portion of the exogenous ammonia was excreted as ammonia. In contrast, feeding is more likely to induce urea synthesis, which is energy intensive, because feeding provides an ample supply of energy resources and leads to the production of ammonia intracellularly in the liver. The capacity of P. dolloi to synthesize urea effectively prevented a postprandial surge in the plasma ammonia level as reported elsewhere for other non-ureogenic teleosts. However, there was a significant increase in the glutamine content in the brain at hour 24, indicating that the brain had to defend against ammonia toxicity after feeding.
Patricia A Wright - One of the best experts on this subject based on the ideXlab platform.
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nitrogen excretion and expression of carbamoyl phosphate synthetase iii activity and mrna in extrahepatic tissues of largemouth bass micropterus salmoides
Archives of Biochemistry and Biophysics, 1998Co-Authors: Haiyan Kong, Joseph J Korte, Wilmar L Salo, Patricia A Wright, Dale D Edberg, Paul M AndersonAbstract:Low levels of all of the enzymes required for urea synthesis via the urea cycle, including mitochondrial glutamine- and acetylglutamate-dependent carbamoyl-phosphate synthetase III (CPSase III) and cytosolic glutamine synthetase, are known to be present in liver of the teleost fish largemouth bass (Micropterus salmoides). The levels of these enzymes are higher than those in most other teleosts, but they are significantly lower than the levels present in liver of ureoosmotic elasmobranchs. The purpose of this study was to assess the physiological role of CPSase III in the context of urea synthesis in adult bass. The results showed that urea–N accounts for about 30% of the total nitrogen (ammonia–N plus urea–N) excreted under control conditions. The rate of urea–N excretion did not increase in response to exposure to 1 mM NH4Cl (3 days) or 0.25 mM NH4Cl (12 days) in the external water, except for a transient increase after a day or two of exposure. CPSase III activity in liver also did not increase in response to exposure to ammonia. Adult largemouth bass, while apparently ureogenic, are primarily Ammonotelic and remain so even in the presence of relatively high concentrations of ammonia in the external environment. The total units of CPSase III activity in liver are not sufficient to account for the quantity of urea that is excreted. However, CPSase III and ornithine carbamoyltransferase (OCTase) activities were found to be present in intestinal tissue and, unexpectedly, in muscle tissue. The total units of CPSase III and OCTase in muscle, intestine, and liver appear to be sufficient to account for the observed rate of urea excretion. The sequence of CPSase III cDNA was determined, which permitted the use of ribonuclease protection assays to demonstrate the presence of CPSase III mRNA in these tissues.
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expression of carbamoyl phosphate synthetase iii mrna during the early stages of development and in muscle of adult rainbow trout oncorhynchus mykiss
Journal of Biological Chemistry, 1997Co-Authors: Joseph J Korte, Wilmar L Salo, Vicente M Cabrera, Patricia A Wright, Andrew K Felskie, Paul M AndersonAbstract:It has been reported that the activities of the urea cycle-related enzymes ornithine carbamoyltransferase and carbamoyl-phosphate synthetase III (CPSase III) are induced during early life stages of Ammonotelic rainbow trout (Oncorhynchus mykiss), suggesting that the urea cycle may play a physiological role in early development in teleost fish (Wright, P. A., Felskie, A., and Anderson, P. M. (1995) J. Exp. Biol. 198, 127-135). CPSase III cDNA prepared from embryo mRNA was sequenced, confirming the existence of the CPSase III gene in trout and its expression. The deduced amino acid sequence of the CPSase III is homologous to other CPSases. Supporting evidence for the expression of CPSase III activity in trout embryos was obtained by demonstrating expression of CPSase III mRNA as early as day 3 post-fertilization, reaching a maximum at 10-14 days, declining to a minimum at day 70, and then increasing to a relatively constant level from days 90 to 110 (relative to total RNA). Unexpectedly, in tissues of adult and fingerling trout, CPSase III mRNA was found to be present in muscle but not in other tissues, including liver. This finding was confirmed by assay of extracts, which showed CPSase III and ornithine carbamoyltransferase activity in muscle but not in other tissues. The pyrimidine nucleotide pathway-related CPSase II mRNA was expressed in all tissues.
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induction of ornithine urea cycle enzymes and nitrogen metabolism and excretion in rainbow trout oncorhynchus mykiss during early life stages
The Journal of Experimental Biology, 1995Co-Authors: Patricia A Wright, A Felskie, Paul M AndersonAbstract:The ornithinesurea cycle (OUC) is present in elasmobranch fish and many terrestrial vertebrates. Recently, a functional OUC has been reported in a few teleost species, suggesting that all teleost fish have the genes for the OUC, but expression is relatively rare. We investigated the possibility that the OUC is expressed during early development in trout as a mechanism for detoxifying ammonia produced from the catabolism of yolk protein. We followed ammonia and urea excretion rates, tissue ammonia and urea levels and OUC enzyme activities in rainbow trout up to 93 days after fertilization. Both ammonia and urea tissue concentrations increased several-fold in the first 40 days after fertilization (embryo stage), peaking at 1.7 mmol N l-1 and 2.5 mmol N l-1, respectively. Ammonia excretion could be detected in 4-day-old embryos, but urea excretion was not initiated until after hatching (day 45). Urea excretion in larval fish (days 42s93) increased several-fold and by day 93 was 14 % of total nitrogen excretion, as found in adult trout. Glutamine synthetase (GSase) and arginase activities were detected in 9whole animal9 homogenates just after hatching and the levels of activity increased markedly to day 93. Carbamoyl phosphate synthetase (CPSase) and ornithine transcarbamylase (OTCase) were first detected in 40-day-old embryos; activities peaked between days 53 and 71 and then subsequently decreased. Adult liver enzyme activity for GSase was several-fold lower than in whole larval trout and OTCase and CPSase III (glutamine- and N-acetylglutamate-dependent CPSase catalysing the first step of the OUC) activities were essentially absent in adult liver. We conclude that embryonic and larval trout are primarily ammoniotelic. Urea is synthesized immediately after fertilization, but is not excreted until after the embryo is hatched. The results provide evidence for the presence of the OUC in larval rainbow trout, since four of the OUC enzymes are induced just after hatching and the levels of activity are relatively high compared with those in adult liver tissue. Furthermore, we suggest that all teleosts have retained the OUC genes, which are expressed only during certain stages of development (embryogenesis), and in a few rare species expression is maintained throughout the life cycle to cope with unusual environmental conditions (e.g. alkaline water, air exposure).