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Tresguerres M, Clifford AM, Harter TS, Roa JN, Thies AB, Yee DP, Brauner CJ. Evolutionary links between intra- and extracellular acid-base regulation in fish and other aquatic animals. JOURNAL OF EXPERIMENTAL ZOOLOGY PART 2020; 333:449-465. [PMID: 32458594 DOI: 10.1002/jez.2367] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/04/2019] [Revised: 03/10/2020] [Accepted: 05/06/2020] [Indexed: 12/17/2022]
Abstract
The acid-base relevant molecules carbon dioxide (CO2 ), protons (H+ ), and bicarbonate (HCO3 - ) are substrates and end products of some of the most essential physiological functions including aerobic and anaerobic respiration, ATP hydrolysis, photosynthesis, and calcification. The structure and function of many enzymes and other macromolecules are highly sensitive to changes in pH, and thus maintaining acid-base homeostasis in the face of metabolic and environmental disturbances is essential for proper cellular function. On the other hand, CO2 , H+ , and HCO3 - have regulatory effects on various proteins and processes, both directly through allosteric modulation and indirectly through signal transduction pathways. Life in aquatic environments presents organisms with distinct acid-base challenges that are not found in terrestrial environments. These include a relatively high CO2 relative to O2 solubility that prevents internal CO2 /HCO3 - accumulation to buffer pH, a lower O2 content that may favor anaerobic metabolism, and variable environmental CO2 , pH and O2 levels that require dynamic adjustments in acid-base homeostatic mechanisms. Additionally, some aquatic animals purposely create acidic or alkaline microenvironments that drive specialized physiological functions. For example, acidifying mechanisms can enhance O2 delivery by red blood cells, lead to ammonia trapping for excretion or buoyancy purposes, or lead to CO2 accumulation to promote photosynthesis by endosymbiotic algae. On the other hand, alkalinizing mechanisms can serve to promote calcium carbonate skeletal formation. This nonexhaustive review summarizes some of the distinct acid-base homeostatic mechanisms that have evolved in aquatic organisms to meet the particular challenges of this environment.
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Affiliation(s)
- Martin Tresguerres
- Marine Biology Research Division, Scripps Institution of Oceanography, University of California, San Diego, California
| | - Alexander M Clifford
- Marine Biology Research Division, Scripps Institution of Oceanography, University of California, San Diego, California
| | - Till S Harter
- Marine Biology Research Division, Scripps Institution of Oceanography, University of California, San Diego, California
| | - Jinae N Roa
- Marine Biology Research Division, Scripps Institution of Oceanography, University of California, San Diego, California
| | - Angus B Thies
- Marine Biology Research Division, Scripps Institution of Oceanography, University of California, San Diego, California
| | - Daniel P Yee
- Marine Biology Research Division, Scripps Institution of Oceanography, University of California, San Diego, California
| | - Colin J Brauner
- Department of Zoology, University of British Columbia, Vancouver, Canada
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Shartau RB, Baker DW, Harter TS, Aboagye DL, Allen PJ, Val AL, Crossley DA, Kohl ZF, Hedrick MS, Damsgaard C, Brauner CJ. Preferential intracellular pH regulation is a common trait amongst fishes exposed to high environmental CO 2. J Exp Biol 2020; 223:jeb208868. [PMID: 32127382 DOI: 10.1242/jeb.208868] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2019] [Accepted: 02/25/2020] [Indexed: 12/13/2022]
Abstract
Acute (<96 h) exposure to elevated environmental CO2 (hypercarbia) induces a pH disturbance in fishes that is often compensated by concurrent recovery of intracellular and extracellular pH (pHi and pHe, respectively; coupled pH regulation). However, coupled pH regulation may be limited at CO2 partial pressure (PCO2 ) tensions far below levels that some fishes naturally encounter. Previously, four hypercarbia-tolerant fishes had been shown to completely and rapidly regulate heart, brain, liver and white muscle pHi during acute exposure to >4 kPa PCO2 (preferential pHi regulation) before pHe compensation was observed. Here, we test the hypothesis that preferential pHi regulation is a widespread strategy of acid-base regulation among fish by measuring pHi regulation in 10 different fish species that are broadly phylogenetically separated, spanning six orders, eight families and 10 genera. Contrary to previous views, we show that preferential pHi regulation is the most common strategy for acid-base regulation within these fishes during exposure to severe acute hypercarbia and that this strategy is associated with increased hypercarbia tolerance. This suggests that preferential pHi regulation may confer tolerance to the respiratory acidosis associated with hypercarbia, and we propose that it is an exaptation that facilitated key evolutionary transitions in vertebrate evolution, such as the evolution of air breathing.
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Affiliation(s)
- R B Shartau
- Department of Zoology, University of British Columbia, Vancouver, BC, Canada V6T 1Z4
| | - D W Baker
- Department of Fisheries and Aquaculture, Vancouver Island University, Nanaimo, BC, Canada V9R 5S5
| | - T S Harter
- Department of Zoology, University of British Columbia, Vancouver, BC, Canada V6T 1Z4
| | - D L Aboagye
- Department of Wildlife, Fisheries and Aquaculture, Mississippi State University, Starkville, MS 39759, USA
| | - P J Allen
- Department of Wildlife, Fisheries and Aquaculture, Mississippi State University, Starkville, MS 39759, USA
| | - A L Val
- Laboratory of Ecophysiology and Molecular Evolution, Brazilian National Institute for Research of the Amazon (INPA), Manaus, AM CEP 69080-971, Brazil
| | - D A Crossley
- Department of Biological Sciences, University of North Texas, Denton, TX 76203-5017, USA
| | - Z F Kohl
- Department of Biological Sciences, University of North Texas, Denton, TX 76203-5017, USA
| | - M S Hedrick
- Department of Biological Sciences, California State University, East Bay, CA 94542, USA
| | - C Damsgaard
- Department of Zoology, University of British Columbia, Vancouver, BC, Canada V6T 1Z4
| | - C J Brauner
- Department of Zoology, University of British Columbia, Vancouver, BC, Canada V6T 1Z4
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Burggren W, Bautista N. Invited review: Development of acid-base regulation in vertebrates. Comp Biochem Physiol A Mol Integr Physiol 2019; 236:110518. [DOI: 10.1016/j.cbpa.2019.06.018] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2019] [Revised: 06/24/2019] [Accepted: 06/25/2019] [Indexed: 12/26/2022]
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Shartau RB, Damsgaard C, Brauner CJ. Limits and patterns of acid-base regulation during elevated environmental CO2 in fish. Comp Biochem Physiol A Mol Integr Physiol 2019; 236:110524. [DOI: 10.1016/j.cbpa.2019.110524] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2019] [Revised: 05/29/2019] [Accepted: 07/07/2019] [Indexed: 01/07/2023]
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Sartori MR, Kohl ZF, Taylor EW, Abe AS, Crossley Ii DA. Blood flow distribution in embryonic common snapping turtles Chelydra serpentina (Reptilia; Chelonia) during acute hypoxia and α-adrenergic regulation. Comp Biochem Physiol A Mol Integr Physiol 2019; 238:110575. [PMID: 31505219 DOI: 10.1016/j.cbpa.2019.110575] [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: 05/04/2019] [Revised: 09/04/2019] [Accepted: 09/05/2019] [Indexed: 10/26/2022]
Abstract
Embryonic turtles have four distinct vascular beds that separately perfuse the developing embryo's body and the extra-embryonic yolk sac, amnion and chorioallantoic membrane (CAM). The mechanisms enabling differential regulation of blood flow through these separate beds, in order to meet the varying demands of the embryo during development, is of current interest. The present investigation followed the changes in blood flow distribution during an acute exposure to hypoxia and after α-adrenergic blockade. We monitored heart rate (fH), mean arterial pressure (Pm), and determined relative blood flow distribution (%Q̇sys) using colored microspheres. At 70% and 90% of the incubation period hypoxia elicited a bradycardia without changing Pm while %Q̇sys was altered only at 70%, increasing to the CAM and liver. Blockade of α-adrenergic responses with phentolamine did not change fH or Pm but increased %Q̇sys to the shell. These results show the capacity of embryos to redistribute cardiac output during acute hypoxia, however α-adrenergic receptors seemed to play a relatively small role in embryonic cardiovascular regulation.
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Affiliation(s)
- Marina R Sartori
- Departamento de Zoologia, Instituto de Biociências, Universidade Estadual Paulista, Campus Rio Claro, SP 13506-900, Brazil; Department of Biological Sciences, Developmental Integrative Biology Cluster, University of North Texas, Denton, TX 76203-5017, USA.
| | - Zachary F Kohl
- Department of Biological Sciences, Developmental Integrative Biology Cluster, University of North Texas, Denton, TX 76203-5017, USA
| | - Edwin W Taylor
- Departamento de Zoologia, Instituto de Biociências, Universidade Estadual Paulista, Campus Rio Claro, SP 13506-900, Brazil; School of Biosciences, University of Birmingham, B15 2TT, UK
| | - Augusto S Abe
- Departamento de Zoologia, Instituto de Biociências, Universidade Estadual Paulista, Campus Rio Claro, SP 13506-900, Brazil
| | - Dane A Crossley Ii
- Department of Biological Sciences, Developmental Integrative Biology Cluster, University of North Texas, Denton, TX 76203-5017, USA
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Filogonio R, Crossley DA. Long term effects of chronic prenatal exposure to hypercarbia on organ growth and cardiovascular responses to adrenaline and hypoxia in common snapping turtles. Comp Biochem Physiol A Mol Integr Physiol 2019; 234:10-17. [DOI: 10.1016/j.cbpa.2019.04.009] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2019] [Revised: 04/11/2019] [Accepted: 04/12/2019] [Indexed: 02/02/2023]
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Fanter CE, Lin Z, Keenan SW, Janzen FJ, Mitchell TS, Warren DE. Development-specific transcriptomic profiling suggests new mechanisms for anoxic survival in the ventricle of overwintering turtles. J Exp Biol 2019; 223:jeb.213918. [DOI: 10.1242/jeb.213918] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2019] [Accepted: 12/18/2019] [Indexed: 12/28/2022]
Abstract
Oxygen deprivation swiftly damages tissues in most animals, yet some species show remarkable abilities to tolerate little or even no oxygen. Painted turtles exhibit a development-dependent tolerance that allows adults to survive anoxia ∼4x longer than hatchlings: adults survive ∼170 days and hatchlings survive ∼40 days at 3°C. We hypothesized this difference is related to development-dependent differences in ventricular gene expression. Using a comparative ontogenetic approach, we examined whole transcriptomic changes before, during, and five days after a 20-day bout of anoxic submergence at 3°C. Ontogeny accounted for more gene expression differences than treatment (anoxia or recovery): 1,175 vs. 237 genes, respectively. Of the 237 differences, 93 could confer protection against anoxia and reperfusion injury, 68 could be injurious, and 20 may be constitutively protective. Especially striking during anoxia was the expression pattern of all 76 annotated ribosomal protein (R-protein) mRNAs, which decreased in anoxia-tolerant adults, but increased in anoxia-sensitive hatchlings, suggesting adult-specific regulation of translational suppression. These genes, along with 60 others that decreased their levels in adults and either increased or remained unchanged in hatchlings, implicate antagonistic pleiotropy as a mechanism to resolve the long-standing question about why hatchling painted turtles overwinter in terrestrial nests, rather than emerge and overwinter in water during their first year. In sum, developmental differences in the transcriptome of the turtle ventricle revealed potentially protective mechanisms that contribute to extraordinary adult-specific anoxia tolerance, and provide a unique perspective on differences between the anoxia-induced molecular responses of anoxia-tolerant or anoxia-sensitive phenotypes within a species.
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Affiliation(s)
- Cornelia E. Fanter
- Saint Louis University, Department of Biology, 3507 Laclede Ave., St. Louis, Missouri, 63103, USA
| | - Zhenguo Lin
- Saint Louis University, Department of Biology, 3507 Laclede Ave., St. Louis, Missouri, 63103, USA
| | - Sarah W. Keenan
- South Dakota School of Mines & Technology, Department of Geology and Geological Engineering, 501 East St. Joseph St., Rapid City, South Dakota, 57701, USA
| | - Fredric J. Janzen
- Iowa State University, Department of Ecology, Evolution and Organismal Biology, 251 Bessey Hall, Ames, Iowa, 50011, USA
| | - Timothy S. Mitchell
- University of Minnesota, Department of Ecology, Evolution and Behavior, 1479 Gortner Ave. Saint Paul, MN, 55108, USA
| | - Daniel E. Warren
- Saint Louis University, Department of Biology, 3507 Laclede Ave., St. Louis, Missouri, 63103, USA
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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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Pelster B, Wood CM. Ionoregulatory and oxidative stress issues associated with the evolution of air-breathing. Acta Histochem 2018; 120:667-679. [PMID: 30177382 DOI: 10.1016/j.acthis.2018.08.012] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Aquatic areas frequently face hypoxic conditions. In order to get sufficient oxygen to support aerobic metabolism, a number of freshwater fish resort to aerial respiration to supplement gill respiration especially in situations with reduced oxygen availability in the water. In many species a concomitant reduction in gill surface area or in gill perfusion reduces possible loss of aerially acquired oxygen to the water at the gills, but it also compromises the ion regulatory capacity of gill tissue. In consequence, the reduced gill contact area with water requires appropriate compensation to maintain ion and acid-base homeostasis, often with important ramifications for other organs. Associated modifications in the structure and function of the gills themselves, the skin, the gut, the kidney, and the physiology of water exchange and ion-linked acid-base regulation are discussed. In air-breathing fish, the gut may gain particular importance for the uptake of ions. In addition, tissues frequently exposed to environmental air encounter much higher oxygen partial pressures than typically observed in fish tissues. Physostomous fish using the swimbladder for aerial respiration, for example, will encounter aerial oxygen partial pressure at the swimbladder epithelium when frequently gulping air in hypoxic water. Hyperoxic conditions or rapid changes in oxygen partial pressures result in an increase in the production of reactive oxygen species (ROS). Accordingly, in air-breathing fish, strategies of ionoregulation may be greatly modified, and the ROS defense capacity of air-exposed tissues is improved.
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Shartau R, Crossley D, Kohl Z, Elsey R, Brauner C. American alligator (Alligator mississippiensis) embryos tightly regulate intracellular pH during a severe acidosis. CAN J ZOOL 2018. [DOI: 10.1139/cjz-2017-0249] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Crocodilian nests naturally experience high CO2 (hypercarbia), which leads to increased blood Pco2 and reduced blood pH (pHe) in embryos; their response to acid–base challenges is not known. During acute hypercarbia, snapping turtle embryos preferentially regulate tissue pH (pHi) against pHe reductions. This is proposed to be associated with CO2 tolerance in reptilian embryos and is not found in adults. In the present study, we investigated pH regulation in American alligator (Alligator mississippiensis (Daudin, 1802)) embryos exposed to 1 h of hypercarbia hypoxia (13 kPa Pco2, 9 kPa Po2). Hypercarbia hypoxia reduced pHe by 0.42 pH unit, while heart and brain pHi increased, with no change in the pHi of other tissues. The results indicate that American alligator embryos preferentially regulate pHi, similar to snapping turtle embryos, which represents a markedly different strategy of acid–base regulation than what is observed in adult reptiles. These findings suggest that preferential pHi regulation may be a strategy of acid–base regulation used by embryonic reptiles.
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Affiliation(s)
- R.B. Shartau
- Department of Zoology, The University of British Columbia, Vancouver, BC V6T 1Z4, Canada
| | - D.A. Crossley
- Department of Biological Sciences, University of North Texas, Denton, TX 76203, USA
| | - Z.F. Kohl
- Department of Biological Sciences, University of North Texas, Denton, TX 76203, USA
| | - R.M. Elsey
- Louisiana Department of Wildlife and Fisheries, Rockefeller Wildlife Refuge, Grand Chenier, LA 70643, USA
| | - C.J. Brauner
- Department of Zoology, The University of British Columbia, Vancouver, BC V6T 1Z4, Canada
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11
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Dhillon RS, Richards JG. Hypoxia induces selective modifications to the acetylome in the brain of zebrafish (Danio rerio). Comp Biochem Physiol B Biochem Mol Biol 2018; 224:79-87. [PMID: 29309913 DOI: 10.1016/j.cbpb.2017.12.018] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2017] [Revised: 12/18/2017] [Accepted: 12/20/2017] [Indexed: 10/18/2022]
Abstract
Reversible protein acetylation is an important regulatory mechanism for modulating protein function. The cellular protein acetylome is in large part dictated by the cellular redox balance, and in particular [NAD+]. While the relationship between hypoxia, redox balance, energy charge and resulting mitochondrial dysfunction has been examined in the context of hypoxia-linked pathologies, little is known about the direct effects of decreases in environmental oxygen on reversible lysine acetylation, and the resulting modifications to mitochondrial metabolism. To address this knowledge gap, we exposed zebrafish (Danio rerio) to 16 h of hypoxia (2.21 kPa) and quantified acetylation levels of 1220 proteins using whole-cell proteomics in samples of brain taken from normoxic and hypoxic zebrafish. In addition, we examined the effects of hypoxia on cytoplasmic and mitochondrial redox status, whole-cell energetics, the activity of the mitochondrial NAD+-dependent deacetylase SIRT3, and electron transport chain complex activities to determine if there is an association between hypoxia-induced metabolic disturbances, protein acetylation, and mitochondrial function. Our results (1) reveal several key changes in the acetylation status of proteins in the brain, primarily within the mitochondria; (2) show significant fluctuations in cytoplasmic and mitochondrial redox status within the brain during hypoxia exposure; and (3) provide evidence that lysine acetylation may be related to large changes in electron transport and ATP-synthase complex activities and adenylate status in zebrafish exposed to hypoxic stress. Together, these data provide new insights into the role of protein modifications in mitochondrial metabolism during hypoxia.
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Affiliation(s)
- Rashpal S Dhillon
- Wisconsin Institute for Discovery, Department of Biomolecular Chemistry, University of Wisconsin-Madison, 330 North Orchard Street, Madison, WI 53715, USA; Department of Zoology, The University of British Columbia, 6270 University Boulevard, Vancouver, BC V6T 1Z4, Canada.
| | - Jeffrey G Richards
- Department of Zoology, The University of British Columbia, 6270 University Boulevard, Vancouver, BC V6T 1Z4, Canada
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Shartau RB, Baker DW, Crossley DA, Brauner CJ. Preferential intracellular pH regulation: hypotheses and perspectives. ACTA ACUST UNITED AC 2017; 219:2235-44. [PMID: 27489212 DOI: 10.1242/jeb.126631] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The regulation of vertebrate acid-base balance during acute episodes of elevated internal PCO2 is typically characterized by extracellular pH (pHe) regulation. Changes in pHe are associated with qualitatively similar changes in intracellular tissue pH (pHi) as the two are typically coupled, referred to as 'coupled pH regulation'. However, not all vertebrates rely on coupled pH regulation; instead, some preferentially regulate pHi against severe and maintained reductions in pHe Preferential pHi regulation has been identified in several adult fish species and an aquatic amphibian, but never in adult amniotes. Recently, common snapping turtles were observed to preferentially regulate pHi during development; the pattern of acid-base regulation in these species shifts from preferential pHi regulation in embryos to coupled pH regulation in adults. In this Commentary, we discuss the hypothesis that preferential pHi regulation may be a general strategy employed by vertebrate embryos in order to maintain acid-base homeostasis during severe acute acid-base disturbances. In adult vertebrates, the retention or loss of preferential pHi regulation may depend on selection pressures associated with the environment inhabited and/or the severity of acid-base regulatory challenges to which they are exposed. We also consider the idea that the retention of preferential pHi regulation into adulthood may have been a key event in vertebrate evolution, with implications for the invasion of freshwater habitats, the evolution of air breathing and the transition of vertebrates from water to land.
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Affiliation(s)
- Ryan B Shartau
- Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada, V6T 1Z4
| | - Daniel W Baker
- Department of Fisheries and Aquaculture, Vancouver Island University, Nanaimo, British Columbia, Canada, V9R 5S5
| | - Dane A Crossley
- Department of Biological Sciences, University of North Texas, Denton, TX 76203-5017, USA
| | - Colin J Brauner
- Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada, V6T 1Z4
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White sturgeon (Acipenser transmontanus) acid-base regulation differs in response to different types of acidoses. J Comp Physiol B 2017; 187:985-994. [PMID: 28283796 DOI: 10.1007/s00360-017-1065-x] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2016] [Revised: 02/02/2017] [Accepted: 02/09/2017] [Indexed: 10/20/2022]
Abstract
White sturgeon (Acipenser transmontanus) completely protect intracellular tissue pH (pHi) despite large reductions in extracellular (blood) pH (pHe), termed preferential pHi regulation, in response to elevated environmental PCO2 (hypercarbia) and in general appear to be relatively resilient to stressors. Preferential pHi regulation is thought to be associated with hypercarbia tolerance in general, but has also recently been observed to protect pHi against metabolic acidoses induced by exhaustive exercise and anoxia in a tropical air breathing catfish. We hypothesized that preferential pHi regulation may also be a general strategy of acid-base regulation in sturgeon. To address this hypothesis, severe acidoses were imposed to reduce pHe, and the presence or absence of preferential pHi regulation was assessed in red blood cells (RBC), heart, brain, liver and white muscle. A respiratory acidosis was imposed using hyperoxia, while metabolic acidoses were induced by exhaustive exercise, anoxia or air exposure. Reductions in pHe occurred following hyperoxia (0.15 units), exhaustive exercise (0.30 units), anoxia (0.10 units) and air exposure (0.35 units); all acidoses reduced RBC pHi. Following hyperoxia, heart, brain and liver pHi were preferentially regulated against the reduction in pHe, similar to hypercarbia exposure. Following all metabolic acidoses heart pHi was protected and brain pHi remained unchanged following exhaustive exercise and air exposure, however, brain pHi was reduced following anoxia. Liver and white muscle pHi were reduced following all metabolic acidoses. These results suggest preferential pHi regulation may be a general strategy during respiratory acidoses but during metabolic acidoses, the response differs between source of acidoses and tissues.
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