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Harter TS, Dichiera AM, Esbaugh AJ. The physiological significance of plasma-accessible carbonic anhydrase in the respiratory systems of fishes. J Comp Physiol B 2024:10.1007/s00360-024-01562-4. [PMID: 38842596 DOI: 10.1007/s00360-024-01562-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2023] [Revised: 04/26/2024] [Accepted: 05/13/2024] [Indexed: 06/07/2024]
Abstract
Carbonic anhydrase (CA) activity is ubiquitously found in all vertebrate species, tissues and cellular compartments. Most species have plasma-accessible CA (paCA) isoforms at the respiratory surfaces, where the enzyme catalyzes the conversion of plasma bicarbonate to carbon dioxide (CO2) that can be excreted by diffusion. A notable exception are the teleost fishes that appear to lack paCA at their gills. The present review: (i) recapitulates the significance of CA activity and distribution in vertebrates; (ii) summarizes the current evidence for the presence or absence of paCA at the gills of fishes, from the basal cyclostomes to the derived teleosts and extremophiles such as the Antarctic icefishes; (iii) explores the contribution of paCA to organismal CO2 excretion in fishes; and (iv) the functional significance of its absence at the gills, for the specialized system of O2 transport in most teleosts; (v) outlines the multiplicity and isoform distribution of membrane-associated CAs in fishes and methodologies to determine their plasma-accessible orientation; and (vi) sketches a tentative time line for the evolutionary dynamics of branchial paCA distribution in the major groups of fishes. Finally, this review highlights current gaps in the knowledge on branchial paCA function and provides recommendations for future work.
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Affiliation(s)
- Till S Harter
- Department of Biology, McMaster University, Hamilton, ON, L8S 4K1, Canada.
| | - Angelina M Dichiera
- College of William and Mary, Virginia Institute of Marine Science, Gloucester Point, VA, 23062, USA
| | - Andrew J Esbaugh
- Marine Science Institute, University of Texas at Austin, Port Aransas, TX, 78373, USA
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2
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Nelson C, Dichiera AM, Brauner CJ. Developing rainbow trout (Oncorhynchus mykiss) lose branchial plasma accessible carbonic anhydrase expression with hatch and the transition to pH-sensitive, adult hemoglobin polymorphs. J Comp Physiol B 2024:10.1007/s00360-024-01557-1. [PMID: 38698121 DOI: 10.1007/s00360-024-01557-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2023] [Revised: 03/03/2024] [Accepted: 04/15/2024] [Indexed: 05/05/2024]
Abstract
Salmonids possess a unique respiratory system comprised of three major components: highly pH-sensitive hemoglobins, red blood cell (RBC) intracellular pH (pHi) protection, and a heterogeneous distribution of plasma accessible carbonic anhydrase (paCA), specifically with absence of paCA at the gills. These characteristics are thought to have evolved to enhance oxygen unloading to the tissues while protecting uptake at the gills. Our knowledge of this system is detailed in adults, but little is known about it through development. Developing rainbow trout (Oncorhynchus mykiss) express embryonic RBCs containing hemoglobins that are relatively insensitive to pH; however, availability of gill paCA and RBC pHi protection is unknown. We show that pre-hatch rainbow trout express gill paCA, which is lost in correlation with the emergence of highly pH-sensitive adult hemoglobins and RBC pHi protection. Rainbow trout therefore exhibit a switch in respiratory strategy with hatch. We conclude that gill paCA likely represents an embryonic trait in rainbow trout and is constrained in adults due to their highly pH-sensitive hemoglobins.
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Affiliation(s)
| | | | - Colin J Brauner
- University of British Columbia, Vancouver, BC, V6T 1Z4, Canada
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3
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Nelson C, Standen EM, Allen PJ, Brauner CJ. An investigation of gill and blood carbonic anhydrase characteristics in three basal actinopterygian species: alligator gar (Atractosteus spatula), white sturgeon (Acipenser transmontanus) and Senegal bichir (Polypterus senegalus). J Comp Physiol B 2024; 194:155-166. [PMID: 38459993 DOI: 10.1007/s00360-024-01539-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2023] [Revised: 12/22/2023] [Accepted: 01/19/2024] [Indexed: 03/11/2024]
Abstract
Many teleosts possess a unique set of respiratory characteristics allowing enhanced oxygen unloading to the tissues during stress. This system comprises three major components: highly pH sensitive haemoglobins (large Bohr and Root effects), rapid red blood cell (RBC) intracellular pH (pHi) protection, and a heterogeneous distribution of membrane-bound plasma-accessible carbonic anhydrase (paCA; absence in the gills). The first two components have received considerable research effort; however, the evolutionary loss of branchial paCA has received little attention. In the current study, we investigated the availability of branchial membrane-bound CA, along with several other CA-related characteristics in species belonging to three basal actinopterygian groups: the Lepisosteiformes, Acipenseriformes and Polypteriformes to assess the earlier hypothesis that Root effect haemoglobins constrain branchial paCA availability. We present the first evidence suggesting branchial membrane-bound CA presence in a basal actinopterygian species: the Senegal bichir (Polypterus senegalus) and show that like the teleosts, white sturgeon (Acipenser transmontanus) and alligator gar (Atractosteus spatula) do not possess branchial membrane-bound CA. We discuss the varying respiratory strategies for these species and propose that branchial paCA may have been lost much earlier than previously thought, likely in relation to the changes in haemoglobin buffer capacity associated with the increasing magnitude of the Bohr effect. The findings described here represent an important advancement in our understanding of the evolution of the unique system of enhanced oxygen unloading thought to be present in most teleosts, a group that encompasses half of all vertebrates.
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Affiliation(s)
| | | | - Peter J Allen
- Mississippi State University, Mississippi, 39762, USA
| | - Colin J Brauner
- University of British Columbia, Vancouver, BC, V6T 1Z4, Canada
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4
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Harter TS, Smith EA, Tresguerres M. A novel perspective on the evolutionary loss of plasma-accessible carbonic anhydrase at the teleost gill. J Exp Biol 2023; 226:jeb246016. [PMID: 37694374 PMCID: PMC10629482 DOI: 10.1242/jeb.246016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2023] [Accepted: 08/31/2023] [Indexed: 09/12/2023]
Abstract
The gills of most teleost fishes lack plasma-accessible carbonic anhydrase (paCA) that could participate in CO2 excretion. We tested the prevailing hypothesis that paCA would interfere with red blood cell (RBC) intracellular pH regulation by β-adrenergic sodium-proton exchangers (β-NHE) that protect pH-sensitive haemoglobin-oxygen (Hb-O2) binding during an acidosis. In an open system that mimics the gills, β-NHE activity increased Hb-O2 saturation during a respiratory acidosis in the presence or absence of paCA, whereas the effect was abolished by NHE inhibition. However, in a closed system that mimics the tissue capillaries, paCA disrupted the protective effects of β-NHE activity on Hb-O2 binding. The gills are an open system, where CO2 generated by paCA can diffuse out and is not available to acidifying the RBCs. Therefore, branchial paCA in teleosts may not interfere with RBC pH regulation by β-NHEs, and other explanations for the evolutionary loss of the enzyme must be considered.
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Affiliation(s)
- Till S. Harter
- Marine Biology Research Division, Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093, USA
| | - Emma A. Smith
- Marine Biology Research Division, Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093, USA
| | - Martin Tresguerres
- Marine Biology Research Division, Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093, USA
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5
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Giareta EP, Hauser-Davis RA, Abilhoa V, Wosnick N. Carbonic anhydrase in elasmobranchs and implications of the current climate change scenario. Comp Biochem Physiol A Mol Integr Physiol 2023; 281:111435. [PMID: 37086909 DOI: 10.1016/j.cbpa.2023.111435] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2023] [Revised: 04/16/2023] [Accepted: 04/17/2023] [Indexed: 04/24/2023]
Abstract
The enzyme carbonic anhydrase (CA) has well-known functions in acid-base balance, respiratory gas exchange, and osmoregulation in teleost fishes. However, studies concerning the role of CA in elasmobranchs are still scarce. Therefore, the aim of this study is to present the current status of CA studies in sharks and rays, as well as to identify gaps and emerging needs, in order to guide future studies. This review is organized according to the main roles of CA, with further considerations on climate change and CA effects indicated as paramount, as strategies in the face of climate change can be crucial for species response. The literature review revealed a reduction in publications on CA over the years. In addition, a historical research differentiation is noted, where the first assessments on the subject addressed investigations on basic CA functions, while the most recent studies present a comparative approach among species as well as interdisciplinary discussions, such as ecology and phylogeny. Considering that most elasmobranchs are threatened, future studies should prioritize non-lethal methodologies, in addition to expanding studies to climate change effects on CA.
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Affiliation(s)
| | - Rachel Ann Hauser-Davis
- Laboratório de Avaliação e Promoção da Saúde Ambiental, Instituto Oswaldo Cruz, Fundação Oswaldo Cruz (Fiocruz), Rio de Janeiro, Brazil
| | - Vinícius Abilhoa
- Programa de Pós-Graduação em Zoologia, Universidade Federal do Paraná, Curitiba, Brazil
| | - Natascha Wosnick
- Programa de Pós-Graduação em Zoologia, Universidade Federal do Paraná, Curitiba, Brazil
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6
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Jeffree RA, Markich SJ, Oberhaensli F, Teyssie JL. Internal distributions of a radio-element array in cartilaginous and bony marine fishes: Different and heterogeneous. JOURNAL OF ENVIRONMENTAL RADIOACTIVITY 2021; 237:106709. [PMID: 34438258 DOI: 10.1016/j.jenvrad.2021.106709] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2021] [Revised: 07/27/2021] [Accepted: 07/29/2021] [Indexed: 06/13/2023]
Abstract
This experimental study determined internal distributions of an array of radio-elements (54Mn, 60Co, 65Zn, 134Cs, 241Am, 109Cd, 110mAg, 75Se and 51Cr) accumulated from seawater by three chondrichthyan fish species (Scyliorhinus canicula (dogfish), Raja undulata (undulate ray) and Torpedo marmorata (spotted torpedo)) and three teleost species (Scophthalmus maximus (turbot), Sparus aurata (seabream) and Dicentrarchus labrax (seabass)). The study tested the hypothesis that the chondrichthyan (cartilaginous) fish taxon and teleost (bony) fish taxon have different patterns of bioaccumulation of these radio-elements in six body components (head, digestive tract, liver, kidneys, skin and muscle), consistent with their long period of evolutionary divergence. Comparisons of body component CFs between the two taxa for each radio-element and the full array of radio-elements showed highly significant differences (p ≤ 0.001) between cartilaginous and bony fishes in each body component, confirming the existence of a strong and pervasive phylogenetic signal; however, the subset of radio-elements most determinant of these differences were unique for each body component. Partitioning between the three individual bony species and the three individual cartilaginous species also occurred repeatedly among their body components, particularly for bony fishes. Distributions of these radio-elements among body components were typically highly heterogeneous for both fish taxa.
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Affiliation(s)
- Ross A Jeffree
- Jeffree Conservation & Research, 45 Casuarina Road, Alfords Point, 2234, Australia.
| | - Scott J Markich
- Aquatic Solutions International, "Point Break", North Narrabeen Beach, NSW, 2101, Australia; Department of Earth and Environmental Sciences, Macquarie University, North Ryde, NSW, 2109, Australia
| | - Francois Oberhaensli
- Marine Radioecology Laboratory, IAEA Environment Laboratories, 4 Quai Antoine, MC, 98000, Monaco
| | - Jean-Louis Teyssie
- Marine Radioecology Laboratory, IAEA Environment Laboratories, 4 Quai Antoine, MC, 98000, Monaco
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7
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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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8
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Dichiera AM, McMillan OJL, Clifford AM, Goss GG, Brauner CJ, Esbaugh AJ. The importance of a single amino acid substitution in reduced red blood cell carbonic anhydrase function of early-diverging fish. J Comp Physiol B 2020; 190:287-296. [PMID: 32146532 DOI: 10.1007/s00360-020-01270-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2019] [Revised: 01/27/2020] [Accepted: 02/12/2020] [Indexed: 02/07/2023]
Abstract
In most vertebrates, red blood cell carbonic anhydrase (RBC CA) plays a critical role in carbon dioxide (CO2) transport and excretion across epithelial tissues. Many early-diverging fishes (e.g., hagfish and chondrichthyans) are unique in possessing plasma-accessible membrane-bound CA-IV in the gills, allowing some CO2 excretion to occur without involvement from the RBCs. However, implications of this on RBC CA function are unclear. Through homology cloning techniques, we identified the putative protein sequences for RBC CA from nine early-diverging species. In all cases, these sequences contained a modification of the proton shuttle residue His-64, and activity measurements from three early-diverging fish demonstrated significantly reduced CA activity. Site-directed mutagenesis was used to restore the His-64 proton shuttle, which significantly increased RBC CA activity, clearly illustrating the functional significance of His-64 in fish red blood cell CA activity. Bayesian analyses of 55 vertebrate cytoplasmic CA isozymes suggested that independent evolutionary events led to the modification of His-64 and thus reduced CA activity in hagfish and chondrichthyans. Additionally, in early-diverging fish that possess branchial CA-IV, there is an absence of His-64 in RBC CAs and the absence of the Root effect [where a reduction in pH reduces hemoglobin's capacity to bind with oxygen (O2)]. Taken together, these data indicate that low-activity RBC CA may be present in all fish with branchial CA-IV, and that the high-activity RBC CA seen in most teleosts may have evolved in conjunction with enhanced hemoglobin pH sensitivity.
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Affiliation(s)
- Angelina M Dichiera
- Marine Science Institute, The University of Texas at Austin, 750 Channel View Drive, Port Aransas, TX, 78373-5015, USA.
| | - Olivia J L McMillan
- Zoology Department, The University of British Columbia, 6270 University Blvd., Vancouver, BC, V6T 1Z4, Canada
| | - Alexander M Clifford
- Scripps Institute of Oceanography, The University of California, San Diego, 9500 Gilman Drive #0202, La Jolla, CA, 92093-0202, USA
| | - Greg G Goss
- Department of Biological Sciences, The University of Alberta, 116 St. and 85 Ave., Edmonton, AB, T6G 2R3, Canada.,Bamfield Marine Sciences Centre, 100 Pachena Road, Bamfield, BC, V0R 1B0, Canada
| | - Colin J Brauner
- Zoology Department, The University of British Columbia, 6270 University Blvd., Vancouver, BC, V6T 1Z4, Canada
| | - Andrew J Esbaugh
- Marine Science Institute, The University of Texas at Austin, 750 Channel View Drive, Port Aransas, TX, 78373-5015, USA
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9
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McMillan OJL, Dichiera AM, Harter TS, Wilson JM, Esbaugh AJ, Brauner CJ. Blood and Gill Carbonic Anhydrase in the Context of a Chondrichthyan Model of CO 2 Excretion. Physiol Biochem Zool 2020; 92:554-566. [PMID: 31567050 DOI: 10.1086/705402] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Pacific spiny dogfish (Squalus suckleyi) have been widely used as a representative species for chondrichthyan CO2 excretion. Pacific spiny dogfish have a slower red blood cell (RBC) carbonic anhydrase (CA) isoform than teleost fishes, extracellular CA activity, no endogenous plasma CA inhibitor, and plasma-accessible CA IV at the gills. Thus, both the RBC and plasma compartments contribute to bicarbonate ion (HCO3-) dehydration at the gills for CO2 excretion in contrast to teleost fishes, in which HCO3- dehydration is restricted to RBCs. We compared CA activity levels, subcellular localization, and presence of plasma CA inhibitors in the blood and gills of 13 chondrichthyans to examine the hypothesis that the dogfish model of CO2 excretion applies broadly to chondrichthyans. In general, blood samples from the 12 other chondrichthyans examined had lower RBC CA activity than teleosts, some extracellular CA activity, and no endogenous plasma CA inhibitor. While type IV-like membrane-associated CA was found in the gills in all four of the chondrichthyans examined, S. suckleyi had three times more CA activity (183±13.2 μmol CO2 min-1 mg protein-1) in the microsomal (membrane) fraction of gills than the other three. In addition, unexpected variation in CA characteristics was observed between chondrichthyan species. Thus, in general, it appears that the pattern of CA distribution in fishes can be generally categorized as either chondrichthyan or teleost models. However, further studies should examine the functional significance of the within-chondrichthyan differences we observed and investigate whether CO2 excretion patterns exist along a continuum or in discrete groups.
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Harter TS, Zanuzzo FS, Supuran CT, Gamperl AK, Brauner CJ. Functional support for a novel mechanism that enhances tissue oxygen extraction in a teleost fish. Proc Biol Sci 2019; 286:20190339. [PMID: 31138074 DOI: 10.1098/rspb.2019.0339] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
A successful spawning migration in salmon depends on their athletic ability, and thus on efficient cardiovascular oxygen (O2) transport. Most teleost fishes have highly pH-sensitive haemoglobins (Hb) that can release large amounts of O2 when the blood is acidified at the tissues. We hypothesized that plasma-accessible carbonic anhydrase (paCA; the enzyme that catalyses proton production from CO2) is required to acidify the blood at the tissues and promote tissue O2 extraction. Previous studies have reported an elevated tissue O2 extraction in hypoxia-acclimated teleosts that may also be facilitated by paCA. Thus, to create experimental contrasts in tissue O2 extraction, Atlantic salmon were acclimated to normoxia or hypoxia (40% air saturation for more than six weeks), and the role of paCA in enhancing tissue O2 extraction was tested by inhibiting paCA at rest and during submaximal exercise. Our results show that: (i) in both acclimation groups, the inhibition of paCA increased cardiac output by one-third, indicating a role of paCA in promoting tissue O2 extraction during exercise, recovery and at rest; (ii) the recruitment of paCA was plastic and increased following hypoxic acclimation; and (iii) maximal exercise performance in salmon, and thus a successful spawning migration, may not be possible without paCA.
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Affiliation(s)
- T S Harter
- 1 Department of Zoology, The University of British Columbia , Vancouver, British Columbia, Canada V6T 1Z4
| | - F S Zanuzzo
- 2 Department of Ocean Sciences, Memorial University of Newfoundland , St John's, Newfoundland, Canada A1C 5S7
| | - C T Supuran
- 3 NEUROFARBA Department, Università degli Studi di Firenze , Florence , Italy
| | - A K Gamperl
- 2 Department of Ocean Sciences, Memorial University of Newfoundland , St John's, Newfoundland, Canada A1C 5S7
| | - C J Brauner
- 1 Department of Zoology, The University of British Columbia , Vancouver, British Columbia, Canada V6T 1Z4
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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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12
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Harter TS, Sackville MA, Wilson JM, Metzger DCH, Egginton S, Esbaugh AJ, Farrell AP, Brauner CJ. A solution to Nature's haemoglobin knockout: a plasma-accessible carbonic anhydrase catalyses CO 2 excretion in Antarctic icefish gills. ACTA ACUST UNITED AC 2018; 221:jeb.190918. [PMID: 30291156 DOI: 10.1242/jeb.190918] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2018] [Accepted: 09/27/2018] [Indexed: 01/29/2023]
Abstract
In all vertebrates studied to date, CO2 excretion depends on the enzyme carbonic anhydrase (CA) that catalyses the rapid conversion of HCO3 - to CO2 at the gas-exchange organs. The largest pool of CA is present within red blood cells (RBCs) and, in some vertebrates, plasma-accessible CA (paCA) isoforms participate in CO2 excretion. However, teleost fishes typically do not have paCA at the gills and CO2 excretion is reliant entirely on RBC CA - a strategy that is not possible in icefishes. As the result of a natural knockout, Antarctic icefishes (Channichthyidae) are the only known vertebrates that do not express haemoglobin (Hb) as adults, and largely lack RBCs in the circulation (haematocrit <1%). Previous work has indicated the presence of high levels of membrane-bound CA activity in the gills of icefishes, but without determining its cellular orientation. Thus, we hypothesised that icefishes express a membrane-bound CA isoform at the gill that is accessible to the blood plasma. The CA distribution was compared in the gills of two closely related notothenioid species, one with Hb and RBCs (Notothenia rossii) and one without (Champsocephalus gunnari). Molecular, biochemical and immunohistochemical markers indicate high levels of a Ca4 isoform in the gills of the icefish (but not the red-blooded N. rossii), in a plasma-accessible location that is consistent with a role in CO2 excretion. Thus, in the absence of RBC CA, the icefish gill could exclusively provide the catalytic activity necessary for CO2 excretion - a pathway that is unlike that of any other vertebrate.
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Affiliation(s)
- Till S Harter
- Department of Zoology, The University of British Columbia, Vancouver, BC V6T 1Z4, Canada
| | - Michael A Sackville
- Department of Zoology, The University of British Columbia, Vancouver, BC V6T 1Z4, Canada
| | - Jonathan M Wilson
- Department of Biology, Wilfrid Laurier University, Waterloo, ON N2L 3C5, Canada
| | - David C H Metzger
- Department of Zoology, The University of British Columbia, Vancouver, BC V6T 1Z4, Canada
| | - Stuart Egginton
- Faculty of Biological Sciences, School of Biomedical Sciences, University of Leeds, Leeds LS2 9JT, UK
| | - Andrew J Esbaugh
- Marine Science Institute, University of Texas at Austin, Port Aransas, TX 78373, USA
| | - Anthony P Farrell
- Department of Zoology, The University of British Columbia, Vancouver, BC V6T 1Z4, Canada.,Faculty of Land and Food Systems, The University of British Columbia, Vancouver, BC V6T 1Z4, Canada
| | - Colin J Brauner
- Department of Zoology, The University of British Columbia, Vancouver, BC V6T 1Z4, Canada
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13
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Harter TS, Brauner CJ. The O 2 and CO 2 Transport System in Teleosts and the Specialized Mechanisms That Enhance Hb–O 2 Unloading to Tissues. ACTA ACUST UNITED AC 2017. [DOI: 10.1016/bs.fp.2017.09.001] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
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14
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Carrie D, Gilmour KM. Phosphorylation increases the catalytic activity of rainbow trout gill cytosolic carbonic anhydrase. J Comp Physiol B 2016; 186:111-22. [PMID: 26498599 DOI: 10.1007/s00360-015-0942-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2015] [Revised: 09/30/2015] [Accepted: 10/11/2015] [Indexed: 11/26/2022]
Abstract
Cytoplasmic carbonic anhydrase (CAc) in the gill of teleost fish contributes to ionic regulation and acid–base balance by catalyzing the reversible reaction of CO2 and water, CO2 + H2O ↔ H(+) + HCO3(-). Regulation of CAc abundance and activity therefore is expected to fine-tune responses to ionic or acid–base challenges. The present study investigated the potential for gill CAc of rainbow trout, Oncorhynchus mykiss (tCAc), to undergo reversible phosphorylation. The activity of tCAc was approximately doubled by phosphorylation achieved through in vitro stimulation of endogenous protein kinases; kinase stimulation doubled phospho-threonine content from that observed in tCAc isolated under conditions where both kinases and protein phosphatases were inhibited. In vitro incubation to preferentially stimulate specific kinases implicated protein kinase G (PKG) in mediating the increase in tCAc activity. The kinetic parameters of turnover number (k cat) and substrate affinity (K m) were similarly affected by stimulation of either kinase or phosphatase action. However, phosphorylation via kinase stimulation significantly increased the efficiency of tCAc (V max /K m), and this factor may have contributed to the elevation of tCAc activity. In addition, phosphorylation of tCAc by kinase stimulation significantly increased the inhibition constant (K i) for acetazolamide. These results demonstrate that tCAc is subject to reversible phosphorylation; future work should focus on identifying the physiological situation(s) in which phosphorylation of trout branchial CAc occurs.
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15
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Milsom WK. New insights into gill chemoreception: Receptor distribution and roles in water and air breathing fish. Respir Physiol Neurobiol 2012; 184:326-39. [DOI: 10.1016/j.resp.2012.07.013] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2012] [Revised: 07/15/2012] [Accepted: 07/17/2012] [Indexed: 12/16/2022]
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Carrie D, Gilmour K. Intracellular carbonic anhydrase contributes to the red blood cell adrenergic response in rainbow trout Oncorhynchus mykiss. Respir Physiol Neurobiol 2012; 184:60-4. [DOI: 10.1016/j.resp.2012.07.022] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2012] [Revised: 07/25/2012] [Accepted: 07/26/2012] [Indexed: 11/28/2022]
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17
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Gilmour KM. New insights into the many functions of carbonic anhydrase in fish gills. Respir Physiol Neurobiol 2012; 184:223-30. [PMID: 22706265 DOI: 10.1016/j.resp.2012.06.001] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2012] [Revised: 05/31/2012] [Accepted: 06/01/2012] [Indexed: 01/25/2023]
Abstract
Carbonic anhydrase (CA) is a zinc metalloenzyme that catalyzes the reversible reactions of carbon dioxide and water: CO(2) + H(2)O ↔ H(+) + HCO(3)(-). It has long been recognized that CA is abundant in the fish gill, with attention focused on the role of CA in catalyzing the hydration of CO(2) to provide H(+) and HCO(3)(-) for the branchial ion transport processes that underlie systemic ionic and acid-base regulation. Recent work has explored the diversity of CA isoforms in the fish gill. By linking these isoforms to different cell types in the gill, and by exploiting the diversity of fish species available for study, this work is increasing our understanding of the many roles that CA plays in the fish gill. In particular, recent work has revealed that fish utilize more than one model of CO(2) excretion, that to understand the role of CA and the gill in ionic regulation and acid-base balance means characterizing the transporter and CA complement of individual cell types, and that CA plays roles in branchial sensory mechanisms. The goal of this brief review is to summarize these new developments, while at the same time highlighting key areas in which further research is needed.
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Affiliation(s)
- Kathleen M Gilmour
- Department of Biology, University of Ottawa, 30 Marie Curie, Ottawa, ON, K1N 6N5, Canada.
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Yamamoto H, Goh K, Magishi K, Sasajima T, Yamamoto F. Blood cardioplegia serves as a bicarbonate donor to the myocardium during ischemia: effects of anoxia and hypercapnia on acid-base characteristics of blood cardioplegic solution. Eur Surg Res 2011; 47:267-73. [PMID: 22075972 DOI: 10.1159/000333365] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2011] [Accepted: 08/15/2011] [Indexed: 11/19/2022]
Abstract
OBJECTIVES We investigated the alterations of acid-base characteristics of the blood cardioplegia (BCP) solution during aortic cross-clamping in hearts arrested with BCP and during in vitro-simulated ischemia. METHODS Following aortic cross-clamping, the hearts of 40 patients undergoing cardiac surgery were intermittently infused with an 18°C BCP solution and finally with a 34°C BCP solution prior to aortic cross-clamp release. We measured the pH, partial CO(2) pressure (pCO(2)), [HCO(3)(-)], and [Cl(-)] of the coronary sinus effluent in the final BCP solution. The BCP solution was assessed under in vitro gassing at 34°C with 95% N(2) + 5% CO(2) (n = 6), 50% N(2) + 50% CO(2) (n = 3), or 100% CO(2) (n = 6). RESULTS The coronary sinus effluent, compared with the preinfusion BCP solution, exhibited a significantly lower pH and a greater pCO(2) with no change in the [HCO(3)(-)] level. In vitro, the 95% N(2) + 5% CO(2) gassing (simulated hypoxia) group exhibited a slight increase in [HCO(3)(-)] with no change in pCO(2) or pH whereas the 50% N(2) + 50% CO(2) gassing and the 100% CO(2) gassing (simulated hypoxia and hypercapnia) groups exhibited a significant increase in [HCO(3)(-)] under high pCO(2)-induced acidification. CONCLUSIONS Under anoxia and CO(2) retention during aortic cross-clamping, the BCP solution can be a bicarbonate donor to the myocardium.
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Affiliation(s)
- H Yamamoto
- Department of Cardiovascular Surgery, Akita University, School of Medicine, Akita, Japan.
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Withers PC, Cooper CE. Using A Priori Contrasts for Multivariate Repeated-Measures ANOVA to Analyze Thermoregulatory Responses of the Dibbler (Parantechinus apicalis; Marsupialia, Dasyuridae). Physiol Biochem Zool 2011; 84:514-21. [DOI: 10.1086/661637] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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20
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Respiratory responses to hypoxia or hypercapnia in goldfish (Carassius auratus) experiencing gill remodelling. Respir Physiol Neurobiol 2010; 175:112-20. [PMID: 20934539 DOI: 10.1016/j.resp.2010.09.018] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2010] [Revised: 09/29/2010] [Accepted: 09/30/2010] [Indexed: 11/22/2022]
Abstract
The presence of an interlamellar cell mass (ILCM) on the gills of goldfish significantly decreases the functional lamellar surface area and increases the diffusion distance for gas transfer and thus may impose a serious challenge for the transfer of respiratory gases (O₂ and CO₂). Here we tested the hypothesis that the presence of the ILCM in goldfish acclimated to 7°C impedes the uptake of O2 and excretion of CO₂. While Pa(O₂) remained unaltered, the baseline values of Pa(CO)₂ were significantly higher in goldfish at 7°C with ILCM present (5.55 ± 0.54 mmHg; mean ± SEM) than in goldfish at 25°C without the ILCM (3.98 ± 0.18 mmHg). Carbonic anhydrase (CA) injections relieved the apparent diffusion limitation imposed by the presence of the ILCM on CO₂ excretion (Pw(CO₂) levels dropped to 3.07 ± 0.32 mmHg). Interestingly, the exposure of fish to acute hypoxia evoked similar changes in Pa(O₂) at the two acclimation temperatures. Ethanol (EtOH) exposure was also used as a tool to further investigate the potential effects of the ILCM on branchial solute transfer. The results showed that the ILCM does not impede EtOH uptake in 7°C goldfish. Overall, the results of this study demonstrate that the remodelling of the goldfish gill associated with acclimation to 7°C water, while increasing Pw(CO₂) , has minimal impact on branchial O2 transfer.
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Gas transfer in dogfish: A unique model of CO2 excretion. Comp Biochem Physiol A Mol Integr Physiol 2010; 155:476-85. [DOI: 10.1016/j.cbpa.2009.10.043] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2009] [Revised: 10/26/2009] [Accepted: 10/29/2009] [Indexed: 11/23/2022]
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Gilmour KM, Thomas K, Esbaugh AJ, Perry SF. Carbonic anhydrase expression and CO2 excretion during early development in zebrafish Danio rerio. ACTA ACUST UNITED AC 2010; 212:3837-45. [PMID: 19915126 DOI: 10.1242/jeb.034116] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Carbonic anhydrase (CA) is critical for CO2 excretion in adult fish, but little is known of the expression or function of CA during early development. The present study examined the hypothesis that, as rates of CO2 production increased during early development in zebrafish (Danio rerio), CA would become necessary for effective CO2 excretion, and that the pattern of CA expression during early development would reflect this transition. Real-time RT-PCR was used to examine the mRNA expression of the two main intracellular CA isoforms over a time course of early development ranging from 0 to 120 h post fertilization (h.p.f.). The mRNA expression of zCAb was generally higher than that of zCAc, particularly during the earliest stages of development. Rates of CO2 excretion increased approximately 15-fold from 24 to 48 h.p.f. whereas rates of O2 uptake increased only 6.7-fold over the same period, indicating a relative stimulation of CO2 excretion over O2 uptake. Treatment of 48 h.p.f. larvae with the CA inhibitor acetazolamide resulted in CO2 excretion rates that were 52% of the value in control larvae, a significant difference that occurred in the absence of any effect on O2 uptake. Antisense morpholino oligonucleotides were used to selectively knock down one or both of the main intracellular CA isoforms. Subsequent measurement of gas transfer rates at 48 h.p.f. indicated that CA knockdown caused a significant relative inhibition of CO2 excretion over O2 uptake, regardless of which cytosolic CA isoform was targeted for knockdown. These results suggest that between 24 h.p.f. and 48 h.p.f., developing zebrafish begin to rely on CA to meet requirements for increased CO2 excretion.
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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.
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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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Esbaugh AJ, Gilmour KM, Perry SF. Membrane-associated carbonic anhydrase in the respiratory system of the Pacific hagfish (Eptatretus stouti). Respir Physiol Neurobiol 2009; 166:107-16. [PMID: 19429527 DOI: 10.1016/j.resp.2009.02.005] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2008] [Revised: 02/10/2009] [Accepted: 02/11/2009] [Indexed: 11/29/2022]
Abstract
Like other agnathans, the Pacific hagfish (Eptatretus stouti) lacks red blood cell (RBC) Cl(-)/HCO(3)(-) exchange. Despite this absence of anion exchange, the majority (86.7+/-1.4%) of the total CO(2) carried in the blood is found within the plasma as HCO(3)(-), and thus presumably is inaccessible to RBC carbonic anhydrase (CA). As such, a branchial plasma-accessible CA isozyme in hagfish would be beneficial for mobilizing the considerable plasma HCO(3)(-) stores for CO(2) excretion and blood acid-base balance. The current study used a combination of molecular and biochemical methods to identify two membrane-associated CA isozymes in the respiratory system of E. stouti. Using homology cloning methods, CA IV and XV-like isozymes were identified in the gill and RBC, respectively. Real-time PCR analysis of relative mRNA expression revealed that CA IV was specific to the gill, while CA XV was found in several tissues including the RBC, gill, liver, heart and muscle. Isolation of subcellular fractions of gill and RBC verified the presence of membrane-associated CA activity in each tissue that persisted after standard washing protocols. Unlike CA activity associated with the cytoplasmic fractions, the activity in gill membranes was not inhibited by sodium dodecyl sulphate, while RBC membrane activity was inhibited to a lesser degree than the cytoplasmic fraction. Additionally, incubation of gill membrane fractions with phosphatidylinositol-specific phospholipase C released significant CA activity into the supernatant indicating the presence of a glycophosphatidyl inositol-linkage to the membrane, as found with other CA IV and XV isozymes. These results demonstrate that Pacific hagfish possess gill and RBC plasma-accessible membrane-associated CA that may play important roles in respiratory gas exchange and acid-base balance.
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Affiliation(s)
- Andrew J Esbaugh
- Department of Biology and Centre for Advanced Research in Environmental Genomics, University of Ottawa, Ottawa, Ontario, Canada K1N 6N5.
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Wood CM, Kajimura M, Mommsen TP, Walsh PJ. Is the alkaline tide a signal to activate metabolic or ionoregulatory enzymes in the dogfish shark (Squalus acanthias)? Physiol Biochem Zool 2008; 81:278-87. [PMID: 18419554 DOI: 10.1086/587094] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Experimental metabolic alkalosis is known to stimulate whole-animal urea production and active ion secretion by the rectal gland in the dogfish shark. Furthermore, recent evidence indicates that a marked alkaline tide (systemic metabolic alkalosis) follows feeding in this species and that the activities of the enzymes of the ornithine-urea cycle (OUC) for urea synthesis in skeletal muscle and liver and of energy metabolism and ion transport in the rectal gland are increased at this time. We therefore evaluated whether alkalosis and/or NaCl/volume loading (which also occurs with feeding) could serve as a signal for activation of these enzymes independent of nutrient loading. Fasted dogfish were infused for 20 h with either 500 mmol L(-1) NaHCO3 (alkalosis + volume expansion) or 500 mmol L(-1) NaCl (volume expansion alone), both isosmotic to dogfish plasma, at a rate of 3 mL kg(-1) h(-1). NaHCO3 infusion progressively raised arterial pH to 8.28 (control = 7.85) and plasma [HCO3-] to 20.8 mmol L(-1) (control = 4.5 mmol L(-1)) at 20 h, with unchanged arterial P(CO2), whereas NaCl/volume loading had no effect on blood acid-base status. Rectal gland Na+,K+-ATPase activity was increased 50% by NaCl loading and more than 100% by NaHCO3 loading, indicating stimulatory effects of both volume expansion and alkalosis. Rectal gland lactate dehydrogenase activity was elevated 25% by both treatments, indicating volume expansion effects only, whereas neither treatment increased the activities of the aerobic enzymes citrate synthase, NADP-isocitrate dehydrogenase, or the ketone body-utilizing enzyme beta-hydroxybutyrate dehydrogenase in the rectal gland or liver. The activity of ornithine-citrulline transcarbamoylase in skeletal muscle was doubled by NaHCO3 infusion, but neither treatment altered the activities of other OUC-related enzymes (glutamine synthetase, carbamoylphosphate synthetase III). We conclude that both the alkaline tide and salt loading/volume expansion act as signals to activate some but not all of the elevated metabolic pathways and ionoregulatory mechanisms needed during processing of a meal.
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Affiliation(s)
- Chris M Wood
- Department of Biology, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada.
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26
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Grosell M, Gilmour KM, Perry SF. Intestinal carbonic anhydrase, bicarbonate, and proton carriers play a role in the acclimation of rainbow trout to seawater. Am J Physiol Regul Integr Comp Physiol 2007; 293:R2099-111. [PMID: 17761514 DOI: 10.1152/ajpregu.00156.2007] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Abrupt transfer of rainbow trout from freshwater to 65% seawater caused transient disturbances in extracellular fluid ionic composition, but homeostasis was reestablished 48 h posttransfer. Intestinal fluid chemistry revealed early onset of drinking and slightly delayed intestinal water absorption that coincided with initiation of NaCl absorption and HCO(3)(-) secretion. Suggestive of involvement in osmoregulation, relative mRNA levels for vacuolar H(+)-ATPase (V-ATPase), Na(+)-K(+)-ATPase, Na(+)/H(+) exchanger 3 (NHE3), Na(+)-HCO(3)(-) cotransporter 1, and two carbonic anhydrase (CA) isoforms [a general cytosolic isoform trout cytoplasmic CA (tCAc) and an extracellular isoform trout membrane-bound CA type IV (tCAIV)], were increased transiently in the intestine following exposure to 65% seawater. Both tCAc and tCAIV proteins were localized to apical regions of the intestinal epithelium and exhibited elevated enzymatic activity after acclimation to 65% seawater. The V-ATPase was localized to both basolateral and apical regions and exhibited a 10-fold increase in enzymatic activity in fish acclimated to 65% seawater, suggesting a role in marine osmoregulation. The intestinal epithelium of rainbow trout acclimated to 65% seawater appears to be capable of both basolateral and apical H(+) extrusion, likely depending on osmoregulatory status and intestinal fluid chemistry.
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Affiliation(s)
- Martin Grosell
- Rosensteil School of Marine Atmospheric Sciences, University of Miami, FL 33149-1098, USA.
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Shuttleworth TJ, Thompson J, Munger RS, Wood CM. A critical analysis of carbonic anhydrase function, respiratory gas exchange, and the acid-base control of secretion in the rectal gland of Squalus acanthias. ACTA ACUST UNITED AC 2007; 209:4701-16. [PMID: 17114403 DOI: 10.1242/jeb.02564] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
We compared in vivo responses of rectal gland secretion to carbonic anhydrase (CA) inhibition (10(-4) mol l(-1) acetazolamide) in volume-loaded dogfish with in vitro responses in an isolated-perfused gland stimulated with 5 x 10(-6) mol l(-1) forskolin and removed from systemic influences. We also measured respiratory gas exchange in the perfused gland, described the acid-base status of the secreted fluid, and determined the relative importance of various extracellular and intracellular acid-base parameters in controlling rectal gland secretion in vitro. In vivo, acetazolamide inhibited Cl(-) secretion and decreased pHi in the rectal gland, but interpretation was confounded by an accompanying systemic respiratory acidosis, which would also have contributed to the inhibition. In the perfused gland, M(CO(2)) and M(O(2)) increased in linear relation to increases in Cl(-) secretion rate. CA inhibition (10(-4) mol l(-1) acetazolamide) had no effect on Cl(-) secretion rate or pHi in the perfused gland, in contrast to in vivo, but caused a transitory 30% inhibition of M(CO(2)) (relative to stable M(O(2))) and elevation in secretion P(CO(2)) effects, which peaked at 2 h and attenuated by 3.5-4 h. Secretion was inhibited by acidosis and stimulated by alkalosis; the relationship between relative Cl(-) secretion rate and pHe was almost identical to that seen in vivo. Experimental manipulations of perfusate pH, P(CO(2)) and HCO(3)(-) concentration, together with measurements of pHi, demonstrated that these responses were most strongly correlated with changes in pHe, and were not related to changes in P(CO(2)), extracellular HCO(3)(-), or intracellular HCO(3)(-) levels, though changes in pHi may also have played a role. The acid-base status of the secreted fluid varied with that of the perfusate, secretion pH remaining about 0.3-0.5 units lower, and changing in concert with pHe rather than pHi; secretion HCO(3)(-) concentrations remained low, even in the face of greatly elevated perfusate HCO(3)(-) concentrations. We conclude that pH effects on rectal gland secretion rate are adaptive, that CA functions to catalyze the hydration of CO(2), thereby maintaining a gradient for diffusive efflux of CO(2) from the working cells, and that differences in response to CA inhibition likely reflect the higher perfusion-to-secretion ratio in vitro than in vivo.
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Affiliation(s)
- Trevor J Shuttleworth
- Department of Pharmacology and Physiology, University of Rochester School of Medicine and Dentistry, Rochester, NY 14642, USA
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Wood CM, Bucking C, Fitzpatrick J, Nadella S. The alkaline tide goes out and the nitrogen stays in after feeding in the dogfish shark, Squalus acanthias. Respir Physiol Neurobiol 2007; 159:163-70. [PMID: 17656159 DOI: 10.1016/j.resp.2007.06.008] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2007] [Revised: 06/11/2007] [Accepted: 06/13/2007] [Indexed: 11/20/2022]
Abstract
In light of previous work showing a marked metabolic alkalosis ("alkaline tide") in the bloodstream after feeding in the dogfish shark (Squalus acanthias), we evaluated whether there was a corresponding net base excretion to the water at this time. In the 48 h after a natural voluntary meal (teleost tissue, averaging 5.5% of body weight), dogfish excreted 10,470 micromol kg(-1) more base (i.e. HCO3- equivalents) than the fasted control animals (which exhibited a negative base excretion of -2160 micromol kg(-1)). This large activation of branchial base excretion after feeding thereby prevented a potentially fatal alkalinization of the body fluids by the alkaline tide. The rate peaked at 330 micromol kg(-1) h(-1) at 12.5-24 h after the meal. Despite a prolonged 1.7-fold elevation in MO2 after feeding ("specific dynamic action"), urea-N excretion decreased by 39% in the same 48 h period relative to fasted controls. In contrast, ammonia-N excretion did not change appreciably. The N/O2 ratio declined from 0.51 in fasted animals to 0.19 in fed sharks, indicating a stimulation of N-anabolic processes at this time. These results, which differ greatly from those in teleost fish, are interpreted in terms of the fundamentally different ureotelic osmoregulatory strategy of elasmobranchs, and recent discoveries on base excretion and urea-retention mechanisms in elasmobranch gills.
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Affiliation(s)
- Chris M Wood
- Department of Biology, McMaster University, 1280 Main St. West, Hamilton, Ontario, Canada L8S 4K1.
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Locomotion in Primitive Fishes. ACTA ACUST UNITED AC 2007. [DOI: 10.1016/s1546-5098(07)26007-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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Gilmour KM, Bayaa M, Kenney L, McNeill B, Perry SF. Type IV carbonic anhydrase is present in the gills of spiny dogfish (Squalus acanthias). Am J Physiol Regul Integr Comp Physiol 2006; 292:R556-67. [PMID: 16973930 DOI: 10.1152/ajpregu.00477.2006] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Physiological and biochemical studies have provided indirect evidence for a membrane-associated carbonic anhydrase (CA) isoform, similar to mammalian type IV CA, in the gills of dogfish (Squalus acanthias). This CA isoform is linked to the plasma membrane of gill epithelial cells by a glycosylphosphatidylinositol anchor and oriented toward the plasma, such that it can catalyze the dehydration of plasma HCO(3)(-) ions. The present study directly tested the hypothesis that CA IV is present in dogfish gills in a location amenable to catalyzing plasma HCO(3)(-) dehydration. Homology cloning techniques were used to assemble a 1,127 base pair cDNA that coded for a deduced protein of 306 amino acids. Phylogenetic analysis suggested that this protein was a type IV CA. For purposes of comparison, a second cDNA (1,107 base pairs) was cloned from dogfish blood; it encoded a deduced protein of 260 amino acids that was identified as a cytosolic CA through phylogenetic analysis. Using real-time PCR and in situ hybridization, mRNA expression for the dogfish type IV CA was detected in gill tissue and specifically localized to pillar cells and branchial epithelial cells that flanked the pillar cells. Immunohistochemistry using a polyclonal antibody raised against rainbow trout type IV CA revealed a similar pattern of CA IV immunoreactivity and demonstrated a limited degree of colocalization with Na(+)-K(+)-ATPase immunoreactivity. The presence and localization of a type IV CA isoform in the gills of dogfish is consistent with the hypothesis that branchial membrane-bound CA with an extracellular orientation contributes to CO(2) excretion in dogfish by catalyzing the dehydration of plasma HCO(3)(-) ions.
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Affiliation(s)
- K M Gilmour
- Department of Biology, University of Ottawa, 30 Marie Curie, Ottawa, ON, Canada K1N 6N5.
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Perry SF, Gilmour KM. Acid-base balance and CO2 excretion in fish: unanswered questions and emerging models. Respir Physiol Neurobiol 2006; 154:199-215. [PMID: 16777496 DOI: 10.1016/j.resp.2006.04.010] [Citation(s) in RCA: 181] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2005] [Revised: 04/14/2006] [Accepted: 04/15/2006] [Indexed: 11/22/2022]
Abstract
Carbon dioxide (CO(2)) excretion and acid-base regulation in fish are linked, as in other animals, though the reversible reactions of CO(2) and the acid-base equivalents H(+) and HCO(3)(-): CO(2)+H(2)O<-->H(+)+HCO(3)(-). These relationships offer two potential routes through which acid-base disturbances may be regulated. Respiratory compensation involves manipulation of ventilation so as to retain CO(2) or enhance CO(2) loss, with the concomitant readjustment of the CO(2) reaction equilibrium and the resultant changes in H(+) levels. In metabolic compensation, rates of direct H(+) and HCO(3)(-) exchange with the environment are manipulated to achieve the required regulation of pH; in this case, hydration of CO(2) yields the necessary H(+) and HCO(3)(-) for exchange. Because ventilation in fish is keyed primarily to the demands of extracting O(2) from a medium of low O(2) content, the capacity to utilize respiratory compensation of acid-base disturbances is limited and metabolic compensation across the gill is the primary mechanism for re-establishing pH balance. The contribution of branchial acid-base exchanges to pH compensation is widely recognized, but the molecular mechanisms underlying these exchanges remain unclear. The relatively recent application of molecular approaches to this question is generating data, sometimes conflicting, from which models of branchial acid-base exchange are gradually emerging. The critical importance of the gill in acid-base compensation in fish, however, has made it easy to overlook other potential contributors. Recently, attention has been focused on the role of the kidney and particularly the molecular mechanisms responsible for HCO(3)(-) reabsorption. It is becoming apparent that, at least in freshwater fish, the responses of the kidney are both flexible and essential to complement the role of the gill in metabolic compensation. Finally, while respiratory compensation in fish is usually discounted, the few studies that have thoroughly characterized ventilatory responses during acid-base disturbances in fish suggest that breathing may, in fact, be adjusted in response to pH imbalances. How this is accomplished and the role it plays in re-establishing acid-base balance are questions that remain to be answered.
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Affiliation(s)
- S F Perry
- Department of Biology and Centre for Advanced Research in Environmental Genomics, University of Ottawa, 30 Marie Curie, Ottawa, Ont., Canada.
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Esbaugh AJ, Tufts BL. The structure and function of carbonic anhydrase isozymes in the respiratory system of vertebrates. Respir Physiol Neurobiol 2006; 154:185-98. [PMID: 16679072 DOI: 10.1016/j.resp.2006.03.007] [Citation(s) in RCA: 116] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2005] [Revised: 03/14/2006] [Accepted: 03/20/2006] [Indexed: 01/12/2023]
Abstract
Carbonic anhydrase is a ubiquitous metalloenzyme that catalyzes the reversible hydration/dehydration of carbon dioxide. To date, 16 different CA isozymes have been identified in mammals, and several novel isozymes have also been identified in non-mammalian vertebrates. These isozymes are involved in many physiological processes; however, one of the most important roles is facilitating the transport and subsequent excretion of carbon dioxide. As such, CA isozymes are found at virtually every step of the process, including the metabolic site of CO(2) production (muscle), the circulating red blood cells, and the primary respiratory surface (gills/lungs). This review will examine the structural characteristics that are integral to CAs participation in respiration, as well as highlight the specific roles and tissues that the different CA isozymes are involved in.
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Affiliation(s)
- A J Esbaugh
- Department of Biology, Queen's University, Kingston, Ont., Canada K7L 3N6.
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Georgalis T, Gilmour KM, Yorston J, Perry SF. Roles of cytosolic and membrane-bound carbonic anhydrase in renal control of acid-base balance in rainbow trout, Oncorhynchus mykiss. Am J Physiol Renal Physiol 2006; 291:F407-21. [PMID: 16571594 DOI: 10.1152/ajprenal.00328.2005] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We tested the hypothesis that cytosolic and membrane-associated carbonic anhydrase (CA IV) are involved in renal urinary acidification and bicarbonate reabsorption in rainbow trout. With the use of homological cloning techniques, a 1,137-bp cDNA was assembled that included an open reading frame encoding for a deduced protein of 297 amino acids. Phylogenetic analysis revealed that this protein was likely a CA IV isoform. With the use of this sequence and a previously described trout cytosolic isoform [tCAc (13)], tools were developed to quantify and localize mRNA and protein for the two CA isoforms. Unlike tCAc, which displayed a broad tissue distribution, trout CA IV mRNA (and to a lesser extent protein) was highly and preferentially expressed in the posterior kidney. The results of in situ hybridization, immunocytochemistry, and standard histological procedures demonstrated that CA IV was likely confined to epithelial cells of the proximal tubule with the protein being expressed on both apical and basolateral membranes. The CA IV-containing tubule cells were enriched with Na(+)-K(+)-ATPase. Similar results were obtained for tCAc except that it appeared to be present in both proximal and distal tubules. The levels of mRNA and protein for tCAc increased significantly during respiratory acidosis (hypercapnia). Although tCA IV mRNA was elevated after 24 h of hypercapnia, tCA IV protein levels were unaltered. By using F3500, a membrane-impermeant (yet filtered) inhibitor of CA, in concert with blood and urine analyses, we demonstrated that CA IV (and possibly other membrane-associated CA isoforms) plays a role in urinary acidification and renal bicarbonate reabsorption.
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Affiliation(s)
- T Georgalis
- Dept. of Biology and Centre for Advanced Research in Environmental Genomics, Univ. of Ottawa, 10 Marie Curie, Ottawa, ON, Canada K1N 6N5
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Georgalis T, Perry SF, Gilmour KM. The role of branchial carbonic anhydrase in acid-base regulation in rainbow trout (Oncorhynchus mykiss). J Exp Biol 2006; 209:518-30. [PMID: 16424102 DOI: 10.1242/jeb.02018] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
SUMMARYThe objective of the present study was to examine the branchial distribution of the recently identified rainbow trout cytoplasmic carbonic anhydrase isoform (tCAc) and to investigate its role in the regulation of acid-base disturbances in rainbow trout (Oncorhynchus mykiss). In situ hybridization using an oligonucleotide probe specific to tCAc revealed tCAc mRNA expression in both pavement cells and mitochondria-rich cells (chloride cells). Similarly, using a homologous polyclonal antibody,tCAc immunoreactivity was localized to pavement cells and mitochondria-rich cells in the interlamellar region and along the lamellae of the gills. Exposure of rainbow trout to hypercarbia (∼0.8% CO2) for 24 h resulted in significant increases in tCAc mRNA expression (∼20-fold;quantified by real-time PCR) and protein levels (∼1.3-fold; quantified by western analysis) but not enzyme activity (assessed on crude gill homogenates using the delta-pH CA assay). Inhibition of branchial CA activity in vivo using acetazolamide reduced branchial net acid excretion significantly by 20%. This effect was enhanced to a 36% reduction in branchial net acid excretion by subjecting the trout to hypercarbia (∼0.8%CO2) for 10 h prior to acetazolamide injection, an exposure that significantly increased branchial net acid excretion. The results of the present study support the widely held premise that branchial intracellular CA activity (tCAc) plays a key role in regulating acid-base balance in freshwater teleost fish.
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Affiliation(s)
- T Georgalis
- Department of Biology and Centre for Advanced Research in Environmental Genomics, University of Ottawa, Ottawa, Ontario, K1N 6N5, Canada
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Wood CM, Kajimura M, Mommsen TP, Walsh PJ. Alkaline tide and nitrogen conservation after feeding in an elasmobranch (Squalus acanthias). ACTA ACUST UNITED AC 2005; 208:2693-705. [PMID: 16000539 DOI: 10.1242/jeb.01678] [Citation(s) in RCA: 100] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
We investigated the consequences of feeding for acid-base balance, nitrogen excretion, blood metabolites and osmoregulation in the Pacific spiny dogfish. Sharks that had been starved for 7 days were surgically fitted with indwelling stomach tubes for gastric feeding and blood catheters for repetitive blood sampling and were confined in chambers, allowing measurement of ammonia-N and urea-N fluxes. The experimental meal infused via the stomach tube consisted of flatfish muscle (2% of body mass) suspended in saline (4% of body mass total volume). Control animals received only saline (4% of body mass). Feeding resulted in a marked rise in both arterial and venous pH and HCO3- concentrations at 3-9 h after the meal, with attenuation by 17 h. Venous P(O2) also fell. As there were negligible changes in P(CO2), the response was interpreted as an alkaline tide without respiratory compensation, associated with elevated gastric acid secretion. Urea-N excretion, which comprised >90% of the total, was unaffected, while ammonia-N excretion was very slightly elevated, amounting to <3% of the total-N in the meal over 45 h. Plasma ammonia-N rose slightly. Plasma urea-N, TMAO-N and glucose concentrations remained unchanged, while free amino acid and beta-hydroxybutyrate levels exhibited modest declines. Plasma osmolality was persistently elevated after the meal relative to controls, partially explained by a significant rise in plasma Cl-. This marked post-prandial conservation of nitrogen is interpreted as reflecting the needs for urea synthesis for osmoregulation and protein growth in animals that are severely N-limited due to their sporadic and opportunistic feeding lifestyle in nature.
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Affiliation(s)
- Chris M Wood
- Department of Biology, McMaster University, 1280 Main St West, Hamilton, Ontario, Canada L8S 4K1.
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Perry SF, Gilmour KM, Swenson ER, Vulesevic B, Chew SF, Ip YK. An investigation of the role of carbonic anhydrase in aquatic and aerial gas transfer in the African lungfishProtopterus dolloi. J Exp Biol 2005; 208:3805-15. [PMID: 16169956 DOI: 10.1242/jeb.01780] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
SUMMARYExperiments were performed on bimodally breathing African lungfish Protopterus dolloi to examine the effects of inhibition of extracellular vs total (extracellular and intracellular) carbonic anhydrase (CA) activity on pulmonary and branchial/cutaneous gas transfer. In contrast to previous studies on Protopterus, which showed that the vast majority of CO2 is excreted into the water through the gill and/or skin whereas O2 uptake largely occurs via the lung, P. dolloi appeared to use the lung for the bulk of both O2uptake (91.0±2.9%) and CO2 excretion (76.0±6.6%). In support of the lung as the more important site of CO2 transfer,aerial hypercapnia (PCO2=40 mmHg) caused a significant rise in partial pressure of arterial blood CO2(PaCO2) whereas a similar degree of aquatic hypercapnia was without effect on PaCO2. Intravascular injection of low levels (1.2 mg kg-1) of the slowly permanent CA inhibitor, benzolamide, was without effect on red blood cell CA activity after 30 min, thus confirming its suitability as a short-term selective inhibitor of extracellular CA. Benzolamide treatment did not affect CO2 excretion, blood acid–base status or any other measured variable within the 30 min measurement period. Injection of the permeant CA inhibitor acetazolamide (30 mg kg-1) resulted in the complete inhibition of red cell CA activity within 10 min. However, CO2excretion (measured for 2 h after injection) and arterial blood acid–base status (assessed for 24 h after injection) were unaffected by acetazolamide treatment. Intra-arterial injection of bovine CA (2 mg kg-1) caused a significant increase in overall CO2excretion (from 0.41±0.03 to 0.58±0.03 mmol kg-1h-1) and an increase in air breathing frequency (from 19.0±1.3 to 24.7±1.8 breaths min-1) that was accompanied by a slight, but significant, reduction in PaCO2 (from 21.6±1.6 to 19.6±1.8 mmHg).The findings of this study are significant because they (i) demonstrate that, unlike in other species of African lungfish that have been examined, the gill/skin is not the major route of CO2 excretion in P. dolloi, and (ii) suggest that CO2 excretion in Protopterus may be less reliant on carbonic anhydrase than in most other fish species.
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Affiliation(s)
- S F Perry
- Department of Biology, University of Ottawa, Canada.
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Esbaugh AJ, Perry SF, Bayaa M, Georgalis T, Nickerson J, Tufts BL, Gilmour KM. Cytoplasmic carbonic anhydrase isozymes in rainbow trout Oncorhynchus mykiss: comparative physiology and molecular evolution. ACTA ACUST UNITED AC 2005; 208:1951-61. [PMID: 15879075 DOI: 10.1242/jeb.01551] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
It is well established that the gills of teleost fish contain substantial levels of cytoplasmic carbonic anhydrase (CA), but it is unclear which CA isozyme(s) might be responsible for this activity. The objective of the current study was to determine if branchial CA activity in rainbow trout was the result of a general cytoplasmic CA isozyme, with kinetic properties, tissue distribution and physiological functions distinct from those of the red blood cell (rbc)-specific CA isozyme. Isolation and sequencing of a second trout cytoplasmic CA yielded a 780 bp coding region that was 76% identical with the trout rbc CA (TCAb), although the active sites differed by only 1 amino acid. Interestingly, phylogenetic analyses did not group these two isozymes closely together, suggesting that more fish species may have multiple cytoplasmic CA isozymes. In contrast to TCAb, the second cytoplasmic CA isozyme had a wide tissue distribution with high expression in the gills and brain, and lower expression in many tissues, including the red blood cells. Thus, unlike TCAb, the second isozyme lacks tissue specificity and may be expressed in the cytoplasm of all cells. For this reason, it is referred to hereafter as TCAc (trout cytoplasmic CA). The inhibitor properties of both cytoplasmic isozymes were similar (Ki acetazolamide 1.21+/-0.18 nmol l(-1) and 1.34+/-0.10 nmol l(-1) for TCAc and TCAb, respectively). However, the turnover of TCAb was over three times greater than that of TCAc (30.3+/-5.83 vs 8.90+/-1.95 e4 s(-1), respectively), indicating that the rbc-specific CA isoform was significantly faster than the general cytoplasmic isoform. Induction of anaemia revealed differential expression of the two isozymes in the red blood cell; whereas TCAc mRNA expression was unaffected, TCAb mRNA expression was significantly increased by 30- to 60-fold in anaemic trout.
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Affiliation(s)
- A J Esbaugh
- Department of Biology, Queen's University, Kingston, ON, Canada K7L 3N6.
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Tresguerres M, Katoh F, Fenton H, Jasinska E, Goss GG. Regulation of branchial V-H(+)-ATPase, Na(+)/K(+)-ATPase and NHE2 in response to acid and base infusions in the Pacific spiny dogfish (Squalus acanthias). ACTA ACUST UNITED AC 2005; 208:345-54. [PMID: 15634853 DOI: 10.1242/jeb.01382] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
To study the mechanisms of branchial acid-base regulation, Pacific spiny dogfish were infused intravenously for 24 h with either HCl (495+/- 79 micromol kg(-1) h(-1)) or NaHCO(3) (981+/-235 micromol kg(-1) h(-1)). Infusion of HCl produced a transient reduction in blood pH. Despite continued infusion of acid, pH returned to normal by 12 h. Infusion of NaHCO(3) resulted in a new steady-state acid-base status at approximately 0.3 pH units higher than the controls. Immunostained serial sections of gill revealed the presence of separate vacuolar proton ATPase (V-H(+)-ATPase)-rich or sodium-potassium ATPase (Na(+)/K(+)-ATPase)-rich cells in all fish examined. A minority of the cells also labeled positive for both transporters. Gill cell membranes prepared from NaHCO(3)-infused fish showed significant increases in both V-H(+)-ATPase abundance (300+/-81%) and activity. In addition, we found that V-H(+)-ATPase subcellular localization was mainly cytoplasmic in control and HCl-infused fish, while NaHCO(3)-infused fish demonstrated a distinctly basolateral staining pattern. Western analysis in gill membranes from HCl-infused fish also revealed increased abundance of Na(+)/H(+) exchanger 2 (213+/-5%) and Na(+)/K(+)-ATPase (315+/-88%) compared to the control.
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Affiliation(s)
- Martin Tresguerres
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta T5G 2E9, Canada.
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Jensen FB. Red blood cell pH, the Bohr effect, and other oxygenation-linked phenomena in blood O2 and CO2 transport. ACTA ACUST UNITED AC 2004; 182:215-27. [PMID: 15491402 DOI: 10.1111/j.1365-201x.2004.01361.x] [Citation(s) in RCA: 198] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The discovery of the S-shaped O2 equilibrium curve and the Bohr effect in 1904 stimulated a fertile and continued research into respiratory functions of blood and allosteric mechanisms in haemoglobin (Hb). The Bohr effect (influence of pH/CO2 on Hb O2 affinity) and the reciprocal Haldane effect (influence of HbO2 saturation on H+/CO2 binding) originate in the Hb oxy-deoxy conformational change and allosteric interactions between O2 and H+/CO2 binding sites. In steady state, H+ is passively distributed across the vertebrate red blood cell (RBC) membrane, and intracellular pH (pHi) changes are related to changes in extracellular pH, Hb-O2 saturation and RBC organic phosphate content. As the Hb molecule shifts between the oxy and deoxy conformation in arterial-venous gas transport, it delivers O2 and takes up CO2 and H+ in tissue capillaries (elegantly aided by the Bohr effect). Concomitantly, the RBC may sense local O2 demand via the degree of Hb deoxygenation and release vasodilatory agents to match local blood flow with requirements. Three recent hypotheses suggest (1) release of NO from S-nitroso-Hb upon deoxygenation, (2) reduction of nitrite to vasoactive NO by deoxy haems, and (3) release of ATP. Inside RBCs, carbonic anhydrase (CA) provides fast hydration of metabolic CO2 and ensures that the Bohr shift occurs during capillary transit. The formed H+ is bound to Hb (Haldane effect) while HCO3- is shifted to plasma via the anion exchanger (AE1). The magnitude of the oxylabile H+ binding shows characteristic differences among vertebrates. Alternative strategies for CO2 transport include direct HCO3- binding to deoxyHb in crocodilians, and high intracellular free [HCO3-] (due to high pHi) in lampreys. At the RBC membrane, CA, AE1 and other proteins may associate into what appears to be an integrated gas exchange metabolon. Oxygenation-linked binding of Hb to the membrane may regulate glycolysis in mammals and perhaps also oxygen-sensitive ion transport involved in RBC volume and pHi regulation. Blood O2 transport shows several adaptive changes during exposure to environmental hypoxia. The Bohr effect is involved via the respiratory alkalosis induced by hyperventilation, and also via the pHi change that results from modulation of RBC organic phosphate content. In teleost fish, beta-adrenergic activation of Na+/H+ exchange rapidly elevates pHi and O2 affinity, particularly under low O2 conditions.
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Affiliation(s)
- F B Jensen
- Institute of Biology, University of Southern Denmark, Odense, Denmark
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41
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Gilmour KM, Perry SF. Branchial membrane-associated carbonic anhydrase activity maintains CO2excretion in severely anemic dogfish. Am J Physiol Regul Integr Comp Physiol 2004; 286:R1138-48. [PMID: 14988082 DOI: 10.1152/ajpregu.00219.2003] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Plasma CO2reactions in Pacific spiny dogfish ( Squalus acanthias) have access to plasma and gill membrane-associated carbonic anhydrase (CA). Acute severe experimental anemia and selective CA inhibitors were used to investigate the role of extracellular CA in CO2excretion. Anemia was induced by blood withdrawal coupled to volume replacement with saline. Lowering hematocrit from 14.2 ± 0.4% (mean ± SE; N = 31) to 5.2 ± 0.1% ( N = 31) had no significant impact on arterial or venous CO2tensions (PaCO2and PvCO2, respectively) over the subsequent 2 h. Pco2was maintained despite the reduction in red cell number and a significant 32% increase in cardiac output (V̇b), both of which have been found to cause PaCO2increases in teleost fish. By contrast, treatment of anemic dogfish with the CA inhibitors benzolamide (1.3 mg/kg) or F3500 (50 mg/kg), to selectively inhibit extracellular CA, elicited rapid and significant increases in PaCO2of 0.68 ± 0.17 Torr ( N = 6) and 0.53 ± 0.11 Torr ( N = 7), respectively, by 30 min after treatment. These findings provide a functional context in which extracellular CA in dogfish contributes substantially to CO2excretion. Additionally, the apparent lack of effect of V̇bchanges on Pco2suggests that, in contrast to teleost fish, CO2excretion in dogfish does not behave as a diffusion-limited system.
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Affiliation(s)
- K M Gilmour
- Bamfiels Marine Station, British Columbia, Canada V0R 1BO.
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Gilmour KM, Desforges PR, Perry SF. Buffering limits plasma HCO3− dehydration when red blood cell anion exchange is inhibited. Respir Physiol Neurobiol 2004; 140:173-87. [PMID: 15134665 DOI: 10.1016/j.resp.2004.02.001] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/06/2004] [Indexed: 11/19/2022]
Abstract
Theory suggests that HCO3- dehydration in the plasma of rainbow trout is limited by both the absence of carbonic anhydrase (CA) activity and the low non-bicarbonate buffer capacity of the plasma (betaplasma). The potential for betaplasma to limit plasma HCO3- dehydration was assessed in rainbow trout in which HCO3- dehydration via the red blood cell (RBC) was inhibited using the anion exchange blocker 4,4'-diisothiocyanostilbene-2,2'-disulphonic acid (DIDS). DIDS administration reduced the rate of RBC HCO3- dehydration by 68-80% for at least 6h, resulting in the elevation of arterial CO2 tension (PaCO2) by 3.07 +/- 0.45 Torr (N = 6). Addition of bovine CA to the circulation of DIDS-treated trout caused PaCO2 to decrease significantly. This effect was increased significantly in rainbow trout in which betaplasma was elevated experimentally by intravascular injection of N-[2-hydroxyethyl]piperazine-N'-[2-ethanesulfonic acid] (HEPES), supporting the hypothesis that CA-catalysed HCO3- dehydration in the plasma of rainbow trout is limited by proton availability.
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Affiliation(s)
- K M Gilmour
- Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, Ont., Canada K1S 5B6.
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Cooper AR, Morris S. Osmotic, sodium, carbon dioxide and acid-base state of the Port Jackson shark, Heterodontus portusjacksoni, in response to lowered salinity. J Comp Physiol B 2003; 174:211-22. [PMID: 14685759 DOI: 10.1007/s00360-003-0404-2] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/20/2003] [Indexed: 10/26/2022]
Abstract
In marine elasmobranch fish the consequences for CO2 and acid-base state of moving into low salinity water are not well described. Sub-adult Port Jackson sharks, Heterodontus portusjacksoni, occasionally enter brackish water and survive in 50% seawater (SW). The unidirectional Na efflux and content, plasma volume, glomerular filtration rate (GFR), body mass, as well as CO2 and acid-base state in H. portusjacksoni were investigated following transfer from 100% SW to 75% SW and then to 50% SW. A rapid water influx resulted in a doubling of the plasma volume within 24 h in sharks in 75% SW and an 11% increase in body weight. Osmotic water influx was only partially offset by a doubling of the GFR. There was a approximately 40% decrease in plasma [Na] through a transiently elevated Na clearance and haemodilution. The result was a decrease in the inward gradient for Na+ together with reductions of nearly 50% in CO2 and buffer capacity. The sharks remained hypo-natric to 50% SW by partially conforming to the decrease in external osmotic pressure and avoided the need for active Na+ uptake. The gradient for Na+ efflux would by extrapolation approach zero at approximately 27% SW which may of itself prove a lethal internal dilution. In sharks transferred to 75% SW, a small transient hypercapnia and a later temporary metabolic alkalosis were all largely explained through anaemia promoting loss of CO2 and buffer capacity. In sharks transferred to 50% SW the metabolic alkalosis persisted until the end of the 1-week trial. Within the erythrocytes, increased pH was consequent on the large decrease in haemoglobin content exhibited by the sharks, which caused a large reduction in intracellular buffer. In water as dilute as 50% SW there was no evidence of specific effects on the mechanisms of management of CO2 or H+ excretion but rather significant and indirect effects of the severe haemodilution.
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Affiliation(s)
- A R Cooper
- School of Biological Sciences, University of Sydney, 2006 Sydney, NSW, Australia
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Stabenau EK, Heming T. Pulmonary carbonic anhydrase in vertebrate gas exchange organs. Comp Biochem Physiol A Mol Integr Physiol 2003; 136:271-9. [PMID: 14511746 DOI: 10.1016/s1095-6433(03)00177-6] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Carbonic anhydrase (CA) catalyzes the interconversion of CO(2) and HCO(3)(-). Intracellular (extravascular) and intravascular (extracellular) CA has been identified and localized in the lungs of reptiles and mammals. Less information is known, however, on the presence of intravascular CA in the lungs of amphibians and avians. In the present study, perfusion studies were used to compare the catalytic activity of pulmonary intravascular CA in reptiles and mammals. In addition, SDS-resistant CA activity was examined in microsomal fractions prepared from gill/lung tissue from representative animals in each vertebrate class. Finally, the CNO(-) sensitivity of the microsomal CA activity was compared. No SDS-resistant CA activity was found in gill microsomal fractions of several fish species. In contrast, the data suggest that SDS-resistant, intravascular pulmonary CA activity is present in air-breathing vertebrates with vastly differing lung morphologies and that the kinetics of inhibition is remarkably comparable between the vertebrate classes.
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Affiliation(s)
- Erich K Stabenau
- Department of Biology, Bradley University, 1501 W. Bradley Ave., Peoria, IL 61625, USA.
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Richards JG, Heigenhauser GJF, Wood CM. Exercise and recovery metabolism in the Pacific spiny dogfish (Squalus acanthias). J Comp Physiol B 2003; 173:463-74. [PMID: 12851779 DOI: 10.1007/s00360-003-0354-8] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/02/2003] [Indexed: 11/28/2022]
Abstract
We examined the effects of exhaustive exercise and post-exercise recovery on white muscle substrate depletion and metabolite distribution between white muscle and blood plasma in the Pacific spiny dogfish, both in vivo and in an electrically stimulated perfused tail-trunk preparation. Measurements of arterial-venous lactate, total ammonia, beta-hydroxybutyrate, glucose, and L-alanine concentrations in the perfused tail-trunk assessed white muscle metabolite fluxes. Exhaustive exercise was fuelled primarily by creatine phosphate hydrolysis and glycolysis as indicated by 62, 71, and 85% decreases in ATP, creatine phosphate, and glycogen, respectively. White muscle lactate production during exercise caused a sustained increase (approximately 12 h post-exercise) in plasma lactate load and a short-lived increase (approximately 4 h post-exercise) in plasma metabolic acid load during recovery. Exhaustive exercise and recovery did not affect arterial PO2, PCO2, or PNH3 but the metabolic acidosis caused a decrease in arterial HCO3- immediately after exercise and during the first 8 h recovery. During recovery, lactate was retained in the white muscle at higher concentrations than in the plasma despite increased lactate efflux from the muscle. Pyruvate dehydrogenase activity was very low in dogfish white muscle at rest and during recovery (0.53 +/- 0.15 nmol g wet tissue(-1) min(-1); n=40) indicating that lactate oxidation is not the major fate of lactate during post-exercise recovery. The lack of change in white muscle free-carnitine and variable changes in short-chain fatty acyl-carnitine suggest that dogfish white muscle does not rely on lipid oxidation to fuel exhaustive exercise or recovery. These findings support the notion that extrahepatic tissues cannot utilize fatty acids as an oxidative fuel. Furthermore, our data strongly suggest that ketone body oxidation is important in fuelling recovery metabolism in dogfish white muscle and at least 20% of the ATP required for recovery could be supplied by uptake and oxidation of beta-hydroxybutyrate from the plasma.
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Affiliation(s)
- J G Richards
- Department of Biology, McMaster University, Hamilton, Ontario, Canada, L8S 4K1.
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Perry SF, Gilmour KM. Sensing and transfer of respiratory gases at the fish gill. THE JOURNAL OF EXPERIMENTAL ZOOLOGY 2002; 293:249-63. [PMID: 12115900 DOI: 10.1002/jez.10129] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The gill is both a site of gas transfer and an important location of chemoreception or gas sensing in fish. While often considered separately, these two processes are clearly intricately related because the gases that are transferred between the ventilatory water and blood at the gill are simultaneously sensed by chemoreceptors on, and within, the gill. Modulation of chemoreceptor discharge in response to changes in O(2) and CO(2) levels, in turn, is believed to initiate a series of coordinated cardiorespiratory reflexes aimed at optimising branchial gas transfer. The past decade has yielded numerous advances in terms of our understanding of gas transfer and gas sensing at the fish gill, particularly concerning the transfer and sensing of carbon dioxide. In addition, recent research has moved from striving to construct a single model that covers all fish species, to recognition of the considerable inter-specific variation that exists with respect to the mechanics of gas transfer and the cardiorespiratory responses of fish to changes in O(2) and CO(2) levels. The following review attempts to integrate gas transfer and gas sensing at the fish gill by exploring recent advances in these areas.
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Affiliation(s)
- Steve F Perry
- Department of Biology, University of Ottawa, Ottawa, Ontario, K1N 6N5 Canada.
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Szebedinszky C, Gilmour KM. The buffering power of plasma in brown bullhead (Ameiurus nebulosus). Comp Biochem Physiol B Biochem Mol Biol 2002; 131:171-83. [PMID: 11818239 DOI: 10.1016/s1096-4959(01)00492-4] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Brown bullhead (Ameiurus nebulosus) blood plasma was found to exhibit an unusually high non-bicarbonate buffer capacity (beta) in relation to that of other teleost fish. In brown bullhead, the non-bicarbonate buffer capacity of plasma (beta(plasma)), at -5.72 +/- 0.34 mmol l(-1) pH unit(-1) (mean +/- S.E.M., N=30), constituted 37% of whole blood beta and was 2.5 times higher than beta(plasma) in rainbow trout (-2.33 +/- 0.42 mmol l(+/-1) pH unit(-1); N=7). The strong buffering power of bullhead plasma was not the result of unusually high plasma protein levels. Size separation chromatography in conjunction with a spectrophotometric assay for buffering capacity were used to isolate a plasma fraction of high buffering power. SDS-polyacrylamide gel electrophoresis revealed that this fraction contained four proteins, but was dominated by a protein of approximately 68-70 kDa molecular mass. On the basis of the amino acid composition of this fraction, the dominant protein was identified as albumin. In comparison to other fish albumins, bullhead albumin appears to be histidine-rich (6.7%). Thus, the unusually high non-bicarbonate buffer capacity of bullhead plasma appears to stem from the presence in the plasma of a histidine-rich albumin.
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Affiliation(s)
- Cheryl Szebedinszky
- Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, ON, Canada K1S 5B6
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Desforges PR, Harman SS, Gilmour KM, Perry SF. Sensitivity of CO2 excretion to blood flow changes in trout is determined by carbonic anhydrase availability. Am J Physiol Regul Integr Comp Physiol 2002; 282:R501-8. [PMID: 11792660 DOI: 10.1152/ajpregu.2002.282.2.r501] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The blood transit time through the gills of rainbow trout (Oncorhynchus mykiss) was modified by manipulation of cardiac output (Vb). The experiments tested the hypothesis that efficiency of CO2 excretion is sensitive to changes in blood flow owing to chemical equilibrium limitations. An extracorporeal blood shunt was used to continuously monitor blood gases in fish in which Vb was elevated (by 13.3 +/- 2.4 ml x min(-1) x kg(-1)) by intravascular saline injection or reduced (by 10.8 +/- 1.8 ml x min(-1) x kg(-1)) by removal of plasma. The arterial partial pressure of CO2 (Pa(CO2); an index of CO2 excretion efficiency) was increased with elevated Vb and was decreased with reduced Vb such that the changes in Pa(CO2) exhibited a significant positive sigmoidal relationship with the changes in Vb (r2 =0.75; P < 0.05). In contrast, there was no significant relationship between changes in the arterial partial pressure of O2 (Pa(O2); an index of O2 uptake efficiency) and changes in Vb (r2 = 0.07; P > 0.05). The intravenous administration of carbonic anhydrase (CA; 10 mg/kg) before vascular volume loading eliminated the increase in Pa(CO2) with increased Vb that was observed in control fish.
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Affiliation(s)
- Patrick R Desforges
- Department of Biology, University of Ottawa, K1N 6N5, Ontario K1S 5B6, Canada
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Perry SF, McKendry JE. The relative roles of external and internal CO2versusH+ in eliciting the cardiorespiratory responses ofSalmo salarandSqualus acanthiasto hypercarbia. J Exp Biol 2001; 204:3963-71. [PMID: 11807114 DOI: 10.1242/jeb.204.22.3963] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
SUMMARYFish breathing hypercarbic water encounter externally elevated PCO2 and proton levels ([H+]) and experience an associated internal respiratory acidosis, an elevation of blood PCO2 and [H+]. The objective of the present study was to assess the potential relative contributions of CO2versus H+ in promoting the cardiorespiratory responses of dogfish (Squalus acanthias) and Atlantic salmon (Salmo salar) to hypercarbia and to evaluate the relative contributions of externally versus internally oriented receptors in dogfish.In dogfish, the preferential stimulation of externally oriented branchial chemoreceptors using bolus injections (50 ml kg–1) of CO2-enriched (4 % CO2) sea water into the buccal cavity caused marked cardiorespiratory responses including bradycardia (–4.1±0.9 min–1), a reduction in cardiac output (–3.2±0.6 ml min–1 kg–1), an increase in systemic vascular resistance (+0.3±0.2 mmHg ml min–1 kg–1), arterial hypotension (–1.6±0.2 mmHg) and an increase in breathing amplitude (+0.3±0.09 mmHg) (means ± s.e.m., N=9–11). Similar injections of CO2-free sea water acidified to the corresponding pH of the hypercarbic water (pH 6.3) did not significantly affect any of the measured cardiorespiratory variables (when compared with control injections). To preferentially stimulate putative internal CO2/H+ chemoreceptors, hypercarbic saline (4 % CO2) was injected (2 ml kg–1) into the caudal vein. Apart from an increase in arterial blood pressure caused by volume loading, internally injected CO2 was without effect on any measured variable.In salmon, injection of hypercarbic water into the buccal cavity caused a bradycardia (–13.9±3.8 min–1), a decrease in cardiac output (–5.3±1.2 ml min–1 kg–1), an increase in systemic resistance (0.33±0.08 mmHg ml min–1 kg–1) and increases in breathing frequency (9.7±2.2 min–1) and amplitude (1.2±0.2 mmHg) (means ± s.e.m., N=8–12). Apart from a small increase in breathing amplitude (0.4±0.1 mmHg), these cardiorespiratory responses were not observed after injection of acidified water.These results demonstrate that, in dogfish and salmon, the external chemoreceptors linked to the initiation of cardiorespiratory responses during hypercarbia are predominantly stimulated by the increase in water PCO2 rather than by the accompanying decrease in water pH. Furthermore, in dogfish, the cardiorespiratory responses to hypercarbia are probably exclusively derived from the stimulation of external CO2 chemoreceptors, with no apparent contribution from internally oriented receptors.
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Affiliation(s)
- S F Perry
- Department of Biology, University of Ottawa, 30 Marie Curie, Ottawa, Ontario, Canada K1N 6N5.
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Abstract
That ventilation in fish is driven by O2 has long been accepted. The O2 ventilatory drive reflects the much lower capacitance of water for O2 than for CO2, and is mediated by O2 receptors that are distributed throughout the gill arches and that monitor both internal and external O2 levels. In recent years, however, evidence has amassed in support of the existence of a ventilatory drive in fish that is keyed to CO2 and/or pH. While ventilatory responses to CO2/pH may be mediated in part by the O2 drive through CO2/pH-induced changes in blood O2 status, CO2/pH also appear to stimulate ventilation directly. The receptors involved in this pathway are as yet unknown, but the experimental evidence available to date supports the involvement of branchial CO2-sensitive chemoreceptors with an external orientation. Internally-oriented CO2-sensitive chemoreceptors may also be involved, although evidence on this point remains equivocal. In the present paper, the evidence for a CO2/pH-keyed ventilatory drive in fish will be reviewed.
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Affiliation(s)
- K M Gilmour
- Department of Biology, Carleton University, 1125 Colonel By Drive, Ont, K1S 5B6, Ottawa, Canada.
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