1
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Clifford AM, Wilkie MP, Edwards SL, Tresguerres M, Goss GG. Dining on the dead in the deep: Active NH 4 + excretion via Na + /H + (NH 4 + ) exchange in the highly ammonia tolerant Pacific hagfish, Eptatretus stoutii. Acta Physiol (Oxf) 2022; 236:e13845. [PMID: 35620804 DOI: 10.1111/apha.13845] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2021] [Revised: 05/22/2022] [Accepted: 05/23/2022] [Indexed: 01/29/2023]
Abstract
AIM Pacific hagfish are exceptionally tolerant to high environmental ammonia (HEA). Here, we elucidated a cellular mechanism that enables hagfish to actively excrete ammonia against steep ammonia gradients expected to be found inside a decomposing whale carcass. METHODS Hagfish were exposed to varying concentrations of HEA in the presence or absence of environmental Na+ , while plasma ammonia levels were tracked. 14 C-methylammonium was used as a proxy for NH4 + to measure efflux in whole animals and in isolated gill pouches; the latter allowed us to assess the effects of amiloride specifically on Na+ /H+ exchangers (NHEs) in gill cells. Western blotting and immunohistochemistry were utilized to evaluate the abundance and sub-cellular localization of Rhesus glycoprotein (Rh) channels in the response to HEA. RESULTS Hagfish actively excreted NH4 + against steep inwardly directed ENH4 + (ΔENH4 + ~ 35 mV) and pNH3 (ΔpNH3 ~ 2000 μtorr) gradients. Active NH4 + excretion and plasma ammonia hypo-regulation were contingent on the presence of environmental Na+ , indicating a Na+ /NH4 + exchange mechanism. Active NH4 + excretion across isolated gill pouches was amiloride-sensitive. Exposure to HEA resulted in decreased abundance of Rh channels in the apical membrane of gill ionocytes. CONCLUSIONS During HEA exposure, hagfish can actively excrete ammonia against a steep concentration gradient using apical NHEs energized by Na+ -K+ -ATPase in gill ionocytes. Additionally, apical Rh channels are removed from the apical membrane, presumably to reduce ammonia loading from the environment. We suggest that this mechanism allows hagfish to maintain tolerable ammonia levels while feeding inside decomposing carrion, allowing them to exploit nutrient-rich food-falls.
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Affiliation(s)
- Alexander M Clifford
- Marine Biology Research Division, Scripps Institution of Oceanography, University of California, La Jolla, California, USA.,Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada.,Bamfield Marine Sciences Centre, Bamfield, British Columbia, Canada
| | - Michael P Wilkie
- Department of Biology and Laurier Institute for Water Science, Wilfrid Laurier University, Waterloo, Ontario, Canada
| | - Susan L Edwards
- Department of Biological Sciences, Wright State University, Dayton, Ohio, USA
| | - Martin Tresguerres
- Marine Biology Research Division, Scripps Institution of Oceanography, University of California, La Jolla, California, USA
| | - Greg G Goss
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada.,Bamfield Marine Sciences Centre, Bamfield, British Columbia, Canada
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2
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Giacomin M, Drummond JM, Supuran CT, Goss GG. The roles of plasma accessible and cytosolic carbonic anhydrases in bicarbonate (HCO 3-) excretion in Pacific hagfish (Eptatretus stoutii). J Comp Physiol B 2022; 192:713-725. [PMID: 36098803 DOI: 10.1007/s00360-022-01459-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2021] [Revised: 08/08/2022] [Accepted: 08/23/2022] [Indexed: 11/29/2022]
Abstract
Pacific hagfish (Eptatretus stoutii) are marine scavengers and feed on decaying animal carrion by burrowing their bodies inside rotten carcasses where they are exposed to several threatening environmental stressors, including hypercapnia (high partial pressures of CO2). Hagfish possess a remarkable capacity to tolerate hypercapnia, and their ability to recover from acid-base disturbances is well known. To deal with the metabolic acidosis resulting from exposure to high CO2, hagfish can mount a rapid elevation of plasma HCO3- concentration (hypercarbia). Once PCO2 is restored, hagfish quickly excrete their HCO3- load, a process that likely involves the enzyme carbonic anhydrase (CA), which catalyzes HCO3- dehydration into CO2 at the hagfish gills. We aimed to characterize the role of branchial CA in CO2/HCO3- clearance from the plasma at the gills of E. stoutii, under control and high PCO2 (hypercapnic) exposure conditions. We assessed the relative contributions of plasma accessible versus intracellular (cytosolic) CA to gill HCO3- excretion by measuring in situ [14C]-HCO3- fluxes. To accomplish this, we employed a novel surgical technique of individual gill pouch arterial perfusion combined with perifusion of the gill afferent to efferent water ducts. [14C]-HCO3- efflux was measured at the gills of fish exposed to control, hypercapnic (48 h) and recovery from hypercapnia conditions (6 h), in the presence of two well-known pharmacological inhibitors of CA, the membrane impermeant C18 (targets membrane bound, plasma accessible CA) and membrane-permeant acetazolamide, which targets all forms of CA, including extracellular and intracellular cytosolic CAs. C18 did not affect HCO3- flux in control fish, whereas acetazolamide resulted in a significant reduction of 72%. In hypercapnic fish, HCO3- fluxes were much higher and perfusion with acetazolamide caused a reduction of HCO3- flux by 38%. The same pattern was observed for fish in recovery, where in all three experimental conditions, there was no significant inhibition of plasma-accessible CA. We also observed no change in CA enzyme activity (measured in vitro) in any of the experimental PCO2 conditions. In summary, our data suggests that there are additional pathways for HCO3- excretion at the gills of hagfish that are independent of plasma-accessible CA.
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Affiliation(s)
- Marina Giacomin
- Department of Biological Sciences, University of Alberta, CW 405, Biological Sciences Bldg., Edmonton, AB, T6G 2E9, Canada. .,Bamfield Marine Science Centre, Bamfield, BC, V0R 1B0, Canada.
| | - Jenna M Drummond
- Department of Biological Sciences, University of Alberta, CW 405, Biological Sciences Bldg., Edmonton, AB, T6G 2E9, Canada.,Bamfield Marine Science Centre, Bamfield, BC, V0R 1B0, Canada
| | - Claudiu T Supuran
- Neurofarba Department, University of Florence, Via Ugo Schiff 6, Florence, Italy
| | - Greg G Goss
- Department of Biological Sciences, University of Alberta, CW 405, Biological Sciences Bldg., Edmonton, AB, T6G 2E9, Canada.,Bamfield Marine Science Centre, Bamfield, BC, V0R 1B0, Canada
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3
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Montgomery DW, Kwan GT, Davison WG, Finlay J, Berry A, Simpson SD, Engelhard GH, Birchenough SNR, Tresguerres M, Wilson RW. Rapid blood acid-base regulation by European sea bass (Dicentrarchus labrax) in response to sudden exposure to high environmental CO2. J Exp Biol 2022; 225:274118. [PMID: 35005768 PMCID: PMC8917447 DOI: 10.1242/jeb.242735] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2021] [Accepted: 12/20/2021] [Indexed: 11/22/2022]
Abstract
Fish in coastal ecosystems can be exposed to acute variations in CO2 of between 0.2 and 1 kPa CO2 (2000–10,000 µatm). Coping with this environmental challenge will depend on the ability to rapidly compensate for the internal acid–base disturbance caused by sudden exposure to high environmental CO2 (blood and tissue acidosis); however, studies about the speed of acid–base regulatory responses in marine fish are scarce. We observed that upon sudden exposure to ∼1 kPa CO2, European sea bass (Dicentrarchus labrax) completely regulate erythrocyte intracellular pH within ∼40 min, thus restoring haemoglobin–O2 affinity to pre-exposure levels. Moreover, blood pH returned to normal levels within ∼2 h, which is one of the fastest acid–base recoveries documented in any fish. This was achieved via a large upregulation of net acid excretion and accumulation of HCO3− in blood, which increased from ∼4 to ∼22 mmol l−1. While the abundance and intracellular localisation of gill Na+/K+-ATPase (NKA) and Na+/H+ exchanger 3 (NHE3) remained unchanged, the apical surface area of acid-excreting gill ionocytes doubled. This constitutes a novel mechanism for rapidly increasing acid excretion during sudden blood acidosis. Rapid acid–base regulation was completely prevented when the same high CO2 exposure occurred in seawater with experimentally reduced HCO3− and pH, probably because reduced environmental pH inhibited gill H+ excretion via NHE3. The rapid and robust acid–base regulatory responses identified will enable European sea bass to maintain physiological performance during large and sudden CO2 fluctuations that naturally occur in coastal environments. Summary: European sea bass exposed to 1 kPa (10,000 µatm) CO2 regulate blood and red cell pH within 2 h and 40 min, respectively, protecting O2 transport capacity, via enhanced gill acid excretion.
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Affiliation(s)
| | - Garfield T Kwan
- Marine Biology Research Division, Scripps Institution of Oceanography, University of California San Diego, 9500 Gilman Drive, La Jolla, CA, 92093, USA.,National Oceanic and Atmospheric Administration Fisheries Service, Southwest Fisheries Science Center, 8901 La Jolla Shores Drive, La Jolla, CA, 92037, USA
| | | | - Jennifer Finlay
- Biosciences, Geoffrey Pope Building, University of Exeter, UK
| | - Alex Berry
- Biosciences, Geoffrey Pope Building, University of Exeter, UK
| | | | - Georg H Engelhard
- Centre for Environment, Fisheries & Aquaculture Science (Cefas), Pakefield Road, Lowestoft, UK.,School of Environmental Sciences, University of East Anglia, Norwich, UK
| | - Silvana N R Birchenough
- Centre for Environment, Fisheries & Aquaculture Science (Cefas), Pakefield Road, Lowestoft, UK
| | - Martin Tresguerres
- Marine Biology Research Division, Scripps Institution of Oceanography, University of California San Diego, 9500 Gilman Drive, La Jolla, CA, 92093, USA
| | - Rod W Wilson
- Biosciences, Geoffrey Pope Building, University of Exeter, UK
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4
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Lonthair J, Dichiera AM, Esbaugh AJ. Mechanisms of acid-base regulation following respiratory alkalosis in red drum (Sciaenops ocellatus). Comp Biochem Physiol A Mol Integr Physiol 2020; 250:110779. [PMID: 32763467 DOI: 10.1016/j.cbpa.2020.110779] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2020] [Revised: 07/29/2020] [Accepted: 07/29/2020] [Indexed: 10/23/2022]
Abstract
Respiratory acidosis and subsequent metabolic compensation are well-studied processes in fish exposed to elevated CO2 (hypercapnia). Yet, such exposures in the marine environment are invariably accompanied by a return of environmental CO2 to atmospheric baselines. This understudied phenomenon has the potential to cause a respiratory alkalosis that would necessitate base excretion. Here we sought to explore this question and the associated physiological mechanisms that may accompany base excretions using the red drum (Sciaenops ocellatus). As expected, when high pCO2 (15,000 μatm CO2) acclimated red drum were transferred to normal pCO2, their net H+ excretion shifted from positive (0.157 ± 0.044 μmol g-1 h-1) to negative (-0.606 ± 0.116 μmol g-1 h-1) in the 2 h post-transfer period. Net H+ excretion returned to control rates during the 3 to 24 h flux period. Gene expression and enzyme activity assays demonstrated that while the acidosis resulted in significant changes in several relevant transporters, no significant changes accompanied the alkalosis phase. Confocal microscopy was used to assess alkalosis-stimulated translocation of V-type H+ ATPase to the basolateral membrane previously seen in other marine species; however, no apparent translocation was observed. Overall, these data demonstrate that fluctuations in environmental CO2 result in both acidic and alkalotic respiratory disturbances; however, red drum maintain sufficient regulatory capacity to accommodate base excretion. Furthermore, this work does not support a role for basolateral VHA translocation in metabolic compensation from a systemic alkalosis in teleosts.
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Affiliation(s)
- Joshua Lonthair
- Marine Science Institute, University of Texas at Austin, Port Aransas, TX 78373, USA; Department of Environmental Conservation, University of Massachusetts Amherst, Amherst, MA 01003, USA; Fisheries Resources Division, Southwest Fisheries Science Center, National Marine Fisheries Service (NMFS), National Oceanic and Atmospheric Administration (NOAA), La Jolla, CA 92037, USA.
| | - Angelina M Dichiera
- Marine Science Institute, University of Texas at Austin, Port Aransas, TX 78373, USA
| | - Andrew J Esbaugh
- Marine Science Institute, University of Texas at Austin, Port Aransas, TX 78373, USA
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5
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Brauner CJ, Shartau RB, Damsgaard C, Esbaugh AJ, Wilson RW, Grosell M. Acid-base physiology and CO2 homeostasis: Regulation and compensation in response to elevated environmental CO2. FISH PHYSIOLOGY 2019. [DOI: 10.1016/bs.fp.2019.08.003] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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6
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Weinrauch AM, Glover CN, Goss GG. Lipid acquisition and tissue storage in hagfish: new insights from an ancient vertebrate. J Comp Physiol B 2018; 189:37-45. [DOI: 10.1007/s00360-018-1196-8] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2018] [Revised: 11/15/2018] [Accepted: 11/22/2018] [Indexed: 11/29/2022]
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7
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Cuoghi I, Lazzaretti C, Mandrioli M, Mola L, Pederzoli A. Immunohistochemical analysis of the distribution of molecules involved in ionic and pH regulation in the lancelet Branchiostoma floridae (Hubbs, 1922). Acta Histochem 2018; 120:33-40. [PMID: 29169695 DOI: 10.1016/j.acthis.2017.10.011] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2017] [Revised: 09/20/2017] [Accepted: 10/30/2017] [Indexed: 11/28/2022]
Abstract
The aim of present work is to analyse the distribution of carbonic anhydrase II (CAII), cystic fibrosis transmembrane regulator (CFTR), vacuolar-type H+-ATPase (V-H+-ATPase), Na+/K+ ATPase, Na+/H+ exchanger (NHE) and SLC26A6 (solute carrier family 26, member 6), also known as pendrin protein, in the lancelet Branchiostoma floridae in order to go in depth in the evolution of osmoregulation and pH regulation in Chordates. In view of their phylogenetic position, lancelets may indeed provide a critical point of reference for studies on osmoregulation evolution in Chordates. The results of present work demonstrated that, except to Na+/K+ ATPase that is strongly expressed in nephridia only, all the other studied molecules are abundantly present in skin, coelomic epithelium, renal papillae and nephridia and hepatic coecum. Thus, it is possible to hypothesize that also in lancelet, as in fish, these organs are involved in pH control and ionic regulation. In the digestive tract of B. floridae, the intestine epithelium was weakly immune-reactive to all tested antibodies, while the hepatic coecum showed an intense immunoreactivity to all molecules. Since in amphioxus the hepatic coecum functions simultaneously as stomach, liver and pancreas, these immunohistochemical results proved the secretion of H+ and HCO3- ions, typical of digestive process. Colocalization studies indicated a co-expression of the studied proteins in all considered organs, excluding NHE and pendrin for renal papillae, since some renal papillae are NHE immunopositive only.
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Affiliation(s)
- Ivan Cuoghi
- Department of Life Sciences, University of Modena and Reggio Emilia, via Campi 213/D, I-41125 Modena, Italy
| | - Clara Lazzaretti
- Department of Life Sciences, University of Modena and Reggio Emilia, via Campi 213/D, I-41125 Modena, Italy
| | - Mauro Mandrioli
- Department of Life Sciences, University of Modena and Reggio Emilia, via Campi 213/D, I-41125 Modena, Italy
| | - Lucrezia Mola
- Department of Life Sciences, University of Modena and Reggio Emilia, via Campi 213/D, I-41125 Modena, Italy.
| | - Aurora Pederzoli
- Department of Life Sciences, University of Modena and Reggio Emilia, via Campi 213/D, I-41125 Modena, Italy
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8
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Clifford AM, Weinrauch AM, Goss GG. Dropping the base: recovery from extreme hypercarbia in the CO2 tolerant Pacific hagfish (Eptatretus stoutii). J Comp Physiol B 2017; 188:421-435. [PMID: 29290001 DOI: 10.1007/s00360-017-1141-2] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2017] [Revised: 11/24/2017] [Accepted: 12/12/2017] [Indexed: 01/13/2023]
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9
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Weinrauch AM, Clifford AM, Goss GG. Post-prandial physiology and intestinal morphology of the Pacific hagfish (Eptatretus stoutii). J Comp Physiol B 2017; 188:101-112. [DOI: 10.1007/s00360-017-1118-1] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2017] [Revised: 07/04/2017] [Accepted: 07/11/2017] [Indexed: 12/26/2022]
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10
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Clifford AM, Bury NR, Schultz AG, Ede JD, Goss BL, Goss GG. Regulation of plasma glucose and sulfate excretion in Pacific hagfish, Eptatretus stoutii is not mediated by 11-deoxycortisol. Gen Comp Endocrinol 2017; 247:107-115. [PMID: 28126345 DOI: 10.1016/j.ygcen.2017.01.022] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/27/2016] [Revised: 01/16/2017] [Accepted: 01/19/2017] [Indexed: 10/20/2022]
Abstract
The goal of this study was to identify whether Pacific hagfish (Eptatretus stoutii) possess glucocorticoid and mineralocorticoid responses and to examine the potential role(s) of four key steroids in these responses. Pacific hagfish were injected with varying amounts of cortisol, corticosterone or 11-deoxycorticosterone (DOC) using coconut oil implants and plasma glucose and gill total-ATPase activity were monitored as indices of glucocorticoid and mineralocorticoid responses. Furthermore, we also monitored plasma glucose and 11-deoxycortisol (11-DOC) levels following exhaustive stress (30 min of agitation) or following repeated infusion with SO42-. There were no changes in gill total-ATPase following implantation with any steroid, with only very small statistical increases in plasma glucose noted in hagfish implanted with either DOC (at 20 and 200mgkg-1 at 7 and 4days post-injection, respectively) or corticosterone (at 100mgkg-1 at 7days post-injection). Following exhaustive stress, hagfish displayed a large and sustained increase in plasma glucose. Repeated infusion of SO42- into hagfish caused increases in both plasma glucose levels and SO42- excretion rate suggesting a regulated glucocorticoid and mineralocorticoid response. However, animals under either condition did not show any significant increases in plasma 11-DOC concentrations. Our results suggest that while there are active glucocorticoid and mineralocorticoid responses in hagfish, 11-DOC does not appear to be involved and the identity and primary function of the steroid in hagfish remains to be elucidated.
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Affiliation(s)
- Alexander M Clifford
- Bamfield Marine Sciences Centre, Bamfield, BC, Canada; Department of Biological Sciences, University of Alberta, Edmonton, AB, Canada
| | - Nicolas R Bury
- Bamfield Marine Sciences Centre, Bamfield, BC, Canada; Diabetes & Nutritional Sciences Division, Kings College, London, UK; Faculty of Health and Life Sciences, University of Suffolk, Suffolk, UK
| | - Aaron G Schultz
- Bamfield Marine Sciences Centre, Bamfield, BC, Canada; Department of Biological Sciences, University of Alberta, Edmonton, AB, Canada
| | - James D Ede
- Bamfield Marine Sciences Centre, Bamfield, BC, Canada; Department of Biological Sciences, University of Alberta, Edmonton, AB, Canada
| | - Brendan L Goss
- Bamfield Marine Sciences Centre, Bamfield, BC, Canada; Department of Biological Sciences, University of Alberta, Edmonton, AB, Canada
| | - Greg G Goss
- Bamfield Marine Sciences Centre, Bamfield, BC, Canada; Department of Biological Sciences, University of Alberta, Edmonton, AB, Canada.
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11
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Allmon EB, Esbaugh AJ. Carbon dioxide induced plasticity of branchial acid-base pathways in an estuarine teleost. Sci Rep 2017; 7:45680. [PMID: 28378831 PMCID: PMC5381225 DOI: 10.1038/srep45680] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2016] [Accepted: 03/02/2017] [Indexed: 12/21/2022] Open
Abstract
Anthropogenic CO2 is expected to drive ocean pCO2 above 1,000 μatm by 2100 – inducing respiratory acidosis in fish that must be corrected through branchial ion transport. This study examined the time course and plasticity of branchial metabolic compensation in response to varying levels of CO2 in an estuarine fish, the red drum, which regularly encounters elevated CO2 and may therefore have intrinsic resilience. Under control conditions fish exhibited net base excretion; however, CO2 exposure resulted in a dose dependent increase in acid excretion during the initial 2 h. This returned to baseline levels during the second 2 h interval for exposures up to 5,000 μatm, but remained elevated for exposures above 15,000 μatm. Plasticity was assessed via gene expression in three CO2 treatments: environmentally realistic 1,000 and 6,000 μatm exposures, and a proof-of-principle 30,000 μatm exposure. Few differences were observed at 1,000 or 6,000 μatm; however, 30,000 μatm stimulated widespread up-regulation. Translocation of V-type ATPase after 1 h of exposure to 30,000 μatm was also assessed; however, no evidence of translocation was found. These results indicate that red drum can quickly compensate to environmentally relevant acid-base disturbances using baseline cellular machinery, yet are capable of plasticity in response to extreme acid-base challenges.
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Affiliation(s)
- Elizabeth B Allmon
- University of Texas at Austin, University of Texas Marine Science Institute, Port Aransas, TX 78373, USA
| | - Andrew J Esbaugh
- University of Texas at Austin, University of Texas Marine Science Institute, Port Aransas, TX 78373, USA
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12
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Tresguerres M. Novel and potential physiological roles of vacuolar-type H+-ATPase in marine organisms. J Exp Biol 2016; 219:2088-97. [DOI: 10.1242/jeb.128389] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
ABSTRACT
The vacuolar-type H+-ATPase (VHA) is a multi-subunit enzyme that uses the energy from ATP hydrolysis to transport H+ across biological membranes. VHA plays a universal role in essential cellular functions, such as the acidification of lysosomes and endosomes. In addition, the VHA-generated H+-motive force can drive the transport of diverse molecules across cell membranes and epithelia for specialized physiological functions. Here, I discuss diverse physiological functions of VHA in marine animals, focusing on recent discoveries about base secretion in shark gills, potential bone dissolution by Osedax bone-eating worms and its participation in a carbon-concentrating mechanism that promotes coral photosynthesis. Because VHA is evolutionarily conserved among eukaryotes, it is likely to play many other essential physiological roles in diverse marine organisms. Elucidating and characterizing basic VHA-dependent mechanisms could help to determine species responses to environmental stress, including (but not limited to) that resulting from climate change.
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Affiliation(s)
- Martin Tresguerres
- Marine Biology Research Division, Scripps Institution of Oceanography, University of California San Diego, 9500 Gilman Drive, SIO mail code 0202, La Jolla, CA 92093, USA
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13
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Edwards SL, Arnold J, Blair SD, Pray M, Bradley R, Erikson O, Walsh PJ. Ammonia excretion in the Atlantic hagfish (Myxine glutinosa) and responses of an Rhc glycoprotein. Am J Physiol Regul Integr Comp Physiol 2015; 308:R769-78. [DOI: 10.1152/ajpregu.00355.2014] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2014] [Accepted: 02/20/2015] [Indexed: 12/21/2022]
Abstract
Hagfishes, the most ancient of the extant craniates, demonstrate a high tolerance for a number of unfavorable environmental conditions, including elevated ammonia. Proposed mechanisms of ammonia excretion in aquatic organisms include vesicular NH4+ transport and release by exocytosis in marine crabs, and passive NH3 diffusion, active NH4+ transport, and paracellular leakage of NH3 or NH4+ across the gills of fishes. Recently, an emerging paradigm suggests that Rhesus glycoproteins play a vital role in ammonia transport in both aquatic invertebrates and vertebrates. This study has identified an Rh glycoprotein ortholog from the gills of Atlantic hagfish. The hagfish Rhcg shares a 56–60% amino acid identity to other vertebrate Rhcg cDNAs. Sequence information was used to produce an anti-hagfish Rhcg (hRhcg) antibody. We have used hRhcg to localize protein expression to epithelial cells of the gill and the skin. In addition, we have quantified hRhcg expression following exposure to elevated plasma ammonia levels. Animals exposed to a 3 mmol/kg NH4Cl load resulted in significantly elevated plasma ammonia concentrations compared with controls for up to 4 h postinjection. This correlated with net ammonia excretion rates that were also significantly elevated for up to 4 h postinjection. Rhcg mRNA expression in both the gill and skin was significantly elevated by 15 min and 1 h, respectively, and hRhcg protein expression in gills was significantly elevated at 2, 4, and 8 h postinjection. These results demonstrate a potential role for Rhcg in the excretion of ammonia in the Atlantic hagfish.
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Affiliation(s)
- Susan L. Edwards
- Department of Biology, Appalachian State University, Boone, North Carolina
- Mount Desert Island Biological Laboratory, Salisbury Cove, Maine; and
| | - Justin Arnold
- Department of Biology, Appalachian State University, Boone, North Carolina
- Mount Desert Island Biological Laboratory, Salisbury Cove, Maine; and
| | - Salvatore D. Blair
- Department of Biology, Appalachian State University, Boone, North Carolina
- Mount Desert Island Biological Laboratory, Salisbury Cove, Maine; and
| | - Margaret Pray
- Department of Biology, Appalachian State University, Boone, North Carolina
- Mount Desert Island Biological Laboratory, Salisbury Cove, Maine; and
| | - Rachel Bradley
- Department of Biology, Appalachian State University, Boone, North Carolina
- Mount Desert Island Biological Laboratory, Salisbury Cove, Maine; and
| | - Olivia Erikson
- Mount Desert Island Biological Laboratory, Salisbury Cove, Maine; and
| | - Patrick J. Walsh
- Department of Biology, University of Ottawa, Ottawa, Ontario, Canada
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14
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Clifford AM, Goss GG, Wilkie MP. Adaptations of a deep sea scavenger: high ammonia tolerance and active NH₄⁺ excretion by the Pacific hagfish (Eptatretus stoutii). Comp Biochem Physiol A Mol Integr Physiol 2014; 182:64-74. [PMID: 25499242 DOI: 10.1016/j.cbpa.2014.12.010] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2014] [Revised: 12/02/2014] [Accepted: 12/03/2014] [Indexed: 12/19/2022]
Abstract
The Pacific hagfish (Eptatretus stoutii) has an exceptional ability to both withstand and recover from exposure to high external ammonia (HEA). This tolerance is likely due to the feeding behavior of this scavenger, which feeds on intermittent food falls of carrion (e.g. fish, large marine mammals) during which time it may be exposed to high concentrations of total ammonia (T(Amm)=NH3+NH4(+)) while burrowed inside the decomposing carcass. Here we exposed hagfish to 20 mmol L(-1) T(Amm) for periods of up to 48 h and then let animals recover in ammonia-free seawater. During the 48 h HEA exposure period, plasma T(Amm) increased 100-fold to over 5000 μmol L(-1) while ammonia excretion (J(amm)) was transiently inhibited. This increase in plasma T(Amm) resulted from NH3 influx down massive inwardly directed ΔP(NH3) gradients, which also led to a short-lived metabolic alkalosis. Plasma [T(Amm)] stabilized after 24-48 h, possibly through a reduction in NH3 permeability across the body surface, which lowered NH3 influx. Ammonia balance was subsequently maintained through the re-establishment of J(amm) against an inwardly directed ΔP(NH3). Calculations of the Nernst potential for ammonia strongly indicated that J(amm) was also taking place against a large inwardly directed NH4(+) electrochemical gradient. Recovery from HEA in ammonia-free water was characterized by a large ammonia washout, and the restoration of plasma TAmm concentrations to near control concentrations. Ammonia clearance was also accompanied by a residual metabolic acidosis, which likely offset the ammonia-induced metabolic alkalosis seen in the early stages of HEA exposure. We conclude that restoration of J(amm) by the Pacific hagfish during ammonia exposure likely involves secondary active transport of NH4(+), possibly mediated by Na(+)/NH4(+) (H(+)) exchange.
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Affiliation(s)
- Alexander M Clifford
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta, T6G 2E9, Canada; Bamfield Marine Sciences Centre, Bamfield, British Columbia, V0R 1B0, Canada.
| | - Greg G Goss
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta, T6G 2E9, Canada; Bamfield Marine Sciences Centre, Bamfield, British Columbia, V0R 1B0, Canada
| | - Michael P Wilkie
- Bamfield Marine Sciences Centre, Bamfield, British Columbia, V0R 1B0, Canada; Biology Department, Wilfrid Laurier University, Waterloo, Ontario, N2L 3C5, Canada
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15
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Huang CY, Lin HC, Lin CH. Effects of hypoxia on ionic regulation, glycogen utilization and antioxidative ability in the gills and liver of the aquatic air-breathing fish Trichogaster microlepis. Comp Biochem Physiol A Mol Integr Physiol 2014; 179:25-34. [PMID: 25218942 DOI: 10.1016/j.cbpa.2014.09.001] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2014] [Revised: 08/11/2014] [Accepted: 09/02/2014] [Indexed: 01/17/2023]
Abstract
We examined the hypothesis that Trichogaster microlepis, a fish with an accessory air-breathing organ, uses a compensatory strategy involving changes in both behavior and protein levels to enhance its gas exchange ability. This compensatory strategy enables the gill ion-regulatory metabolism to maintain homeostasis during exposure to hypoxia. The present study aimed to determine whether ionic regulation, glycogen utilization and antioxidant activity differ in terms of expression under hypoxic stresses; fish were sampled after being subjected to 3 or 12h of hypoxia and 12h of recovery under normoxia. The air-breathing behavior of the fish increased under hypoxia. No morphological modification of the gills was observed. The expression of carbonic anhydrase II did not vary among the treatments. The Na(+)/K(+)-ATPase enzyme activity did not decrease, but increases in Na(+)/K(+)-ATPase protein expression and ionocyte levels were observed. The glycogen utilization increased under hypoxia as measured by glycogen phosphorylase protein expression and blood glucose level, whereas the glycogen content decreased. The enzyme activity of several components of the antioxidant system in the gills, including catalase, glutathione peroxidase, and superoxidase dismutase, increased in enzyme activity. Based on the above data, we concluded that T. microlepis is a hypoxia-tolerant species that does not exhibit ion-regulatory suppression but uses glycogen to maintain energy utilization in the gills under hypoxic stress. Components of the antioxidant system showed increased expression under the applied experimental treatments.
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Affiliation(s)
- Chun-Yen Huang
- Department of Life Science, Tunghai University, Taichung 40704, Taiwan; Department of Chemistry, National Taiwan Normal University, Taipei 11677, Taiwan
| | - Hui-Chen Lin
- Department of Life Science, Tunghai University, Taichung 40704, Taiwan; Center for Tropical Ecology and Biodiversity, Tunghai University, Taichung 40704, Taiwan.
| | - Cheng-Huang Lin
- Department of Chemistry, National Taiwan Normal University, Taipei 11677, Taiwan
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16
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Expression of carbonic anhydrase, cystic fibrosis transmembrane regulator (CFTR) and V-H(+)-ATPase in the lancelet Branchiostoma lanceolatum (Pallas, 1774). Acta Histochem 2014; 116:487-92. [PMID: 24220283 DOI: 10.1016/j.acthis.2013.10.005] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2013] [Revised: 10/07/2013] [Accepted: 10/08/2013] [Indexed: 12/20/2022]
Abstract
Sequencing of the amphioxus genome revealed that it contains a basic set of chordate genes involved in development and cell signaling. Despite the availability of genomic data, up till now no studies have been addressed on the comprehension of the amphioxus osmoregulation. Using primers designed on Branchiostoma floridae carbonic anhydrase (CA) II, cystic fibrosis transmembrane regulator (CFTR) and V-H(+)-ATPase, a 100bp long region, containing the protein region recognized by the respective antibodies, has been amplified and sequenced in B. lanceolatum indicating the presence of hortologous V-ATPase, CFTR and carbonic anhydrase II genes in Branchiostoma lanceolatum. Immunohistochemical results showed that all three transporting proteins are expressed in almost 90% of epithelial cells of the skin in B. lanceolatum adults with a different degree of positivity in different regions of body wall and with a different localization in the cells. The comparison of results between young and adult lancelets showed that the distribution of these transporters is quite different. Indeed, in the young specimens the expression pattern of all tested molecules appears concentrated at the gut level, whereas in adult the gut loses its key role that is mostly supported by skin.
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17
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Larsen EH, Deaton LE, Onken H, O'Donnell M, Grosell M, Dantzler WH, Weihrauch D. Osmoregulation and Excretion. Compr Physiol 2014; 4:405-573. [DOI: 10.1002/cphy.c130004] [Citation(s) in RCA: 127] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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18
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Extrabranchial mechanisms of systemic pH recovery in hagfish (Eptatretus stoutii). Comp Biochem Physiol A Mol Integr Physiol 2014; 168:82-9. [DOI: 10.1016/j.cbpa.2013.11.009] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2013] [Revised: 11/14/2013] [Accepted: 11/20/2013] [Indexed: 11/19/2022]
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19
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Tresguerres M, Katz S, Rouse GW. How to get into bones: proton pump and carbonic anhydrase in Osedax boneworms. Proc Biol Sci 2013; 280:20130625. [PMID: 23760644 DOI: 10.1098/rspb.2013.0625] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Osedax are gutless siboglinid worms that thrive on vertebrate bones lying on the ocean floor, mainly those of whales. The posterior body of female Osedax penetrates into the bone forming extensions known as 'roots', which host heterotrophic symbiotic bacteria in bacteriocytes beneath the epidermis. The Osedax root epithelium presumably absorbs bone collagen and/or lipids, which are metabolized by the symbiotic bacteria that in turn serve for Osedax's nutrition. Here, we show that Osedax roots express extremely high amounts of vacuolar-H(+)-ATPase (VHA), which is located in the apical membrane and in cytoplasmic vesicles of root and ovisac epithelial cells. The enzyme carbonic anhydrase (CA), which catalyses the hydration of CO2 into H(+) and HCO3(-), is also expressed in roots and throughout Osedax body. These results suggest Osedax roots have massive acid-secreting capacity via VHA, fuelled by H(+) derived from the CA-catalysed hydration of CO2 produced by aerobic metabolism. We propose the secreted acid dissolves the bone carbonate matrix to then allow the absorption of bone-derived nutrients across the skin. In an exciting example of convergent evolution, this model for acid secretion is remarkably similar to mammalian osteoclast cells. However, while osteoclasts dissolve bone for repairing and remodelling, the Osedax root epithelium secretes acid to dissolve foreign bone to access nutrients.
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Affiliation(s)
- Martin Tresguerres
- Marine Biology Research Division, Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 93092-0202, USA.
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20
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Huang CY, Lin HC. The effect of acidity on gill variations in the aquatic air-breathing fish, Trichogaster lalius. Comp Biochem Physiol A Mol Integr Physiol 2011; 158:61-71. [DOI: 10.1016/j.cbpa.2010.09.004] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2010] [Revised: 09/06/2010] [Accepted: 09/07/2010] [Indexed: 11/27/2022]
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21
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Tang CH, Hwang LY, Lee TH. Chloride channel ClC-3 in gills of the euryhaline teleost, Tetraodon nigroviridis: expression, localization and the possible role of chloride absorption. ACTA ACUST UNITED AC 2010; 213:683-93. [PMID: 20154183 DOI: 10.1242/jeb.040212] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Previous studies have reported the mechanisms of ion absorption and secretion by diverse membrane transport proteins in gills of various teleostean species. To date, however, the chloride channel expressed in the basolateral membrane of mitochondrion-rich (MR) cells for Cl(-) uptake in freshwater (FW) fish is still unknown. In this study, the combination of bioinformatics tools [i.e. National Center for Biotechnology Information (NCBI) database, Tetraodon nigroviridis (spotted green pufferfish) genome database (Genoscope), BLAT and BLASTn] were used to identify the gene of ClC-3 (TnClC-3), a member of the CLC chloride channel family in the T. nigroviridis genome. RT-PCR analysis revealed that the gene encoding for the ClC-3 protein was widely expressed in diverse tissues (i.e. gill, kidney, intestine, liver and brain) of FW- and seawater (SW)-acclimated pufferfish. In whole-mount double immunofluorescent staining, branchial ClC-3-like immunoreactive protein was localized to the basolateral membrane of Na(+)/K(+)-ATPase (NKA) immunoreactive cells in both the FW- and SW-acclimated pufferfish. In response to salinity, the levels of transcript of branchial TnClC-3 were similar between FW and SW fish. Moreover, the membrane fraction of ClC-3-like protein in gills was 2.7-fold higher in FW compared with SW pufferfish. To identify whether the expression of branchial ClC-3-like protein specifically responded to lower environmental [Cl(-)], the pufferfish were acclimated to artificial waters either with a normal (control) or lower Cl(-) concentration (low-Cl). Immunoblotting of membrane fractions of gill ClC-3-like protein showed the expression was about 4.3-fold higher in pufferfish acclimated to the low-Cl environment than in the control group. Furthermore, branchial ClC-3-like protein was rapidly elevated in response to acute changes of environmental salinity or [Cl(-)]. Taken together, pufferfish ClC-3-like protein was expressed in the basolateral membrane of gill MR cells, and the protein amounts were stimulated by hyposmotic and low-Cl environments. The enhancement of ClC-3-like protein may trigger the step of basolateral Cl(-) absorption of the epithelium to carry out iono- and osmoregulatory functions of euryhaline pufferfish gills.
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Affiliation(s)
- Cheng-Hao Tang
- Department of Life Sciences, National Chung-Hsing University, Taichung 402, Taiwan
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22
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Huang CY, Chao PL, Lin HC. Na+/K+-ATPase and vacuolar-type H+-ATPase in the gills of the aquatic air-breathing fish Trichogaster microlepis in response to salinity variation. Comp Biochem Physiol A Mol Integr Physiol 2009; 155:309-18. [PMID: 19931636 DOI: 10.1016/j.cbpa.2009.11.010] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2009] [Revised: 11/10/2009] [Accepted: 11/10/2009] [Indexed: 11/25/2022]
Abstract
The aquatic air-breathing fish, Trichogaster microlepis, can be found in fresh water and estuaries. We further evaluated the changes in two important osmoregulatory enzymes, Na(+)/K(+)-ATPase (NKA) and vacuolar-type H(+)-ATPase (VHA), in the gills when fish were subjected to deionized water (DW), fresh water (FW), and salinated brackish water (salinity of 10 g/L). Fish were sampled only 4 days after experimental transfer. The mortality, plasma osmolality, and Na(+) concentration were higher in 10 g/L acclimated fish, while their muscle water content decreased with elevated external salinity. The highest NKA protein abundance was found in the fish gills in 10 g/L, and NKA activity was highest in the DW and 10 g/L acclimated fish. The VHA protein levels were highest in 10 g/L, and VHA activity was highest in the DW treatment. From immunohistochemical results, we found three different cell populations: (1) NKA-immunoreactive (NKA-IR) cells, (2) both NKA-IR and HA-IR cells, and (3) HA-IR cells. NKA-IR cells in the lamellar and interlamellar regions significantly increased in DW and 10 g/L treatments. Only HA-IR cells in the lamellar region were significantly increased in DW. In the interlamellar region, there was no difference in the number of HA-IR cells among the three treated. From these results, T. microlepis exhibited osmoregulatory ability in DW and 10 g/L treatments. The cell types involved in ionic regulation were also examined with immunofluorescence staining; three ionocyte types were found which were similar to the zebrafish model.
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Affiliation(s)
- Chun-Yen Huang
- Department of Life Science, Tunghai University, Taichung 40704, Taiwan
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23
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Weihrauch D, Wilkie MP, Walsh PJ. Ammonia and urea transporters in gills of fish and aquatic crustaceans. J Exp Biol 2009; 212:1716-30. [PMID: 19448081 DOI: 10.1242/jeb.024851] [Citation(s) in RCA: 179] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The diversity of mechanisms of ammonia and urea excretion by the gills and other epithelia of aquatic organisms, especially fish and crustaceans, has been studied for decades. Although the decades-old dogma of ;aquatic species excrete ammonia' still explains nitrogenous waste excretion for many species, it is clear that there are many mechanistic variations on this theme. Even within species that are ammonoteles, the process is not purely ;passive', often relying on the energizing effects of proton and sodium-potassium ATPases. Within the ammonoteles, Rh (Rhesus) proteins are beginning to emerge as vital ammonia conduits. Many fishes are also known to be capable of substantial synthesis and excretion of urea as a nitrogenous waste. In such species, members of the UT family of urea transporters have been identified as important players in urea transport across the gills. This review attempts to draw together recent information to update the mechanisms of ammonia and urea transport by the gills of aquatic species. Furthermore, we point out several potentially fruitful avenues for further research.
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Affiliation(s)
- Dirk Weihrauch
- Department of Biological Sciences, University of Manitoba, 190 Dysart Road, Winnipeg, MB, R3T 2N2 Canada
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Abstract
SUMMARY
Carbonic anhydrase (CA) is the zinc metalloenzyme that catalyses the reversible reactions of CO2 with water. CA plays a crucial role in systemic acid–base regulation in fish by providing acid–base equivalents for exchange with the environment. Unlike air-breathing vertebrates, which frequently utilize alterations of breathing (respiratory compensation) to regulate acid–base status, acid–base balance in fish relies almost entirely upon the direct exchange of acid–base equivalents with the environment (metabolic compensation). The gill is the critical site of metabolic compensation, with the kidney playing a supporting role. At the gill, cytosolic CA catalyses the hydration of CO2 to H+ and HCO3– for export to the water. In the kidney, cytosolic and membrane-bound CA isoforms have been implicated in HCO3– reabsorption and urine acidification. In this review, the CA isoforms that have been identified to date in fish will be discussed together with their tissue localizations and roles in systemic acid–base regulation.
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Affiliation(s)
- K. M. Gilmour
- Department of Biology and Centre for Advanced Research in Environmental Genomics, University of Ottawa, Ottawa, ON, Canada
| | - S. F. Perry
- Department of Biology and Centre for Advanced Research in Environmental Genomics, University of Ottawa, Ottawa, ON, Canada
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25
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Horng JL, Lin LY, Hwang PP. Functional regulation of H+-ATPase-rich cells in zebrafish embryos acclimated to an acidic environment. Am J Physiol Cell Physiol 2009; 296:C682-92. [PMID: 19211913 DOI: 10.1152/ajpcell.00576.2008] [Citation(s) in RCA: 76] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
It is important to maintain internal pH homeostasis in biological systems. In our previous studies, H(+)-ATPase-rich (HR) cells were found to be responsible for proton secretion in the skin of zebrafish embryos during development. In this study, zebrafish embryos were exposed to acidic and basic waters to investigate the regulation of HR cell acid secretion during pH disturbances. Our results showed that the function of HR cells on the skin of zebrafish embryos can be upregulated in pH 4 water not only by increasing the cell number but also by enlarging the acid-secreting function of single cells. We also identified an "alveolar-type" apical opening under scanning electron microscopy observations of the apical membrane of HR cells, and the density and size of the alveolar type of apical openings were also increased in pH 4 water. p63 and PCNA immunostaining results also showed that additional HR cells in pH 4 water may be differentiated not only from ionocyte precursor cells but also newly proliferating epithelial stem cells.
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Affiliation(s)
- Jiun-Lin Horng
- Institute of Cellular and Organismic Biology, Academia Sinica, Taipei, Taiwan, Republic of China
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26
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Parks SK, Tresguerres M, Goss GG. Theoretical considerations underlying Na(+) uptake mechanisms in freshwater fishes. Comp Biochem Physiol C Toxicol Pharmacol 2008; 148:411-8. [PMID: 18420463 DOI: 10.1016/j.cbpc.2008.03.002] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/12/2008] [Revised: 03/04/2008] [Accepted: 03/05/2008] [Indexed: 11/18/2022]
Abstract
Ion and acid-base regulating mechanisms have been studied at the fish gill for almost a century. Original models proposed for Na(+) and Cl(-) uptake, and their linkage with H(+) and HCO(3)(-) secretion have changed substantially with the development of more sophisticated physiological techniques. At the freshwater fish gill, two dominant mechanisms for Na(+) uptake from dilute environments have persisted in the literature. The use of an apical Na(+)/H(+) exchanger driven by a basolateral Na(+)/K(+)-ATPase versus an apical Na(+) channel electrogenically coupled to an apical H(+)-ATPase have been the source of debate for a number of years. Advances in molecular biology have greatly enhanced our understanding of the basic ion transport mechanisms at the fish gill. However, it is imperative to ensure that thermodynamic principles are followed in the development of new models for gill ion transport. This review will focus on the recent molecular advances for Na(+) uptake in freshwater fish. Emphasis will be placed on thermodynamic constraints that prevent electroneutral apical NHE function in most freshwater environments. By combining recent advances in molecular and functional physiology of fish gills with thermodynamic considerations of ion transport, our knowledge in the field should continue to grow in a logical manner.
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Affiliation(s)
- Scott K Parks
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada T5G 2E9
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27
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Tresguerres M, Parks SK, Sabatini SE, Goss GG, Luquet CM. Regulation of ion transport by pH and [HCO3−] in isolated gills of the crabNeohelice(Chasmagnathus)granulata. Am J Physiol Regul Integr Comp Physiol 2008; 294:R1033-43. [DOI: 10.1152/ajpregu.00516.2007] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Posterior isolated gills of Neohelice ( Chasmagnathus) granulatus were symmetrically perfused with hemolymph-like saline of varying [HCO3−] and pH. Elevating [HCO3−] in the saline from 2.5 to 12.5 mmol/l (pH 7.75 in both cases) induced a significant increase in the transepithelial potential difference ( Vte), a measure of ion transport. The elevation in [HCO3−] also induced a switch from acid secretion (−43.7 ± 22.5 μequiv·kg−1·h−1) in controls to base secretion (84.7 ± 14.4 μequiv·kg−1·h−1). The HCO3−-induced Vteincrease was inhibited by basolateral acetazolamide (200 μmol/l), amiloride (1 mmol/l), and ouabain (5 mmol/l) but not by bafilomycin (100 nmol/l). The Vteresponse to HCO3−did not take place in Cl−-free conditions; however, it was unaffected by apical SITS (2 mmol/l) or DIDS (1 mmol/l). A decrease in pH from 7.75 to 7.45 pH units in the perfusate also induced a significant increase in Vte, which was matched by a net increase in acid secretion of 67.8 ± 18.4 μequiv kg−1h−1. This stimulation was sensitive to basolateral acetazolamide, bafilomycin, DIDS, and Na+-free conditions, but it still took place in Cl−-free saline. Therefore, the cellular response to low pH is different from the HCO3−-stimulated response. We also report V-H+-ATPase- and Na+-K+-ATPase-like immunoreactivity in gill sections for the first time in this crab. Our results suggest that carbonic anhydrase (CA), basolateral Na+/H+exchangers and Na+-K+-ATPase and apical anion exchangers participate in the HCO3−-stimulated response, while CA, apical V-H+-ATPase and basolateral HCO3−-dependent cotransporters mediate the response to low pH.
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Parks SK, Tresguerres M, Goss GG. Blood and gill responses to HCl infusions in the Pacific hagfish (Eptatretus stoutii). CAN J ZOOL 2007. [DOI: 10.1139/z07-068] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Pacific hagfish ( Eptatretus stoutii (Lockington, 1878)) were serially infused with HCl (6000 µmol·kg–1) every 6 h over a 24 h period to explore branchial acid secretion mechanisms. Blood pH recovered from a value ~2 pH units below that of resting pH. This pH regulatory mechanism was activated by 6 h and persisted over the 24 h time course. Western-blot analysis revealed an increased abundance (~2.3×) of NHE2-like immunoreactivity (NHE2 L-IR) in whole gill fractions from HCl-infused fish compared with control NaCl-infused fish. Membrane fractions isolated from the gills of HCl-infused fish also showed an increased abundance (~1.8×). Immunohistochemistry results demonstrated a significant redistribution of NHE2 L-IR to the apical region in HCl-infused fish. V-H+-ATPase abundance did not significantly increase in HCl-infused fish, while levels of Na+/K+-ATPase expression were unchanged. Immunohistochemistry of these transporters did not show any changes in cellular localization. We propose that the Pacific hagfish overcomes a metabolic acidosis via an increased synthesis of an NHE-like protein and an increased density of the transporter at the apical region of the mitochondria-rich cells of the gill.
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Affiliation(s)
- Scott K. Parks
- Department of Biological Sciences, University of Alberta, Edmonton, AB T5G 2E9, Canada
| | - Martin Tresguerres
- Department of Biological Sciences, University of Alberta, Edmonton, AB T5G 2E9, Canada
| | - Greg G. Goss
- Department of Biological Sciences, University of Alberta, Edmonton, AB T5G 2E9, Canada
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