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Zimmer AM. Ammonia excretion by the fish gill: discoveries and ideas that shaped our current understanding. J Comp Physiol B 2024:10.1007/s00360-024-01561-5. [PMID: 38849577 DOI: 10.1007/s00360-024-01561-5] [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: 12/15/2023] [Revised: 03/06/2024] [Accepted: 05/15/2024] [Indexed: 06/09/2024]
Abstract
The fish gill serves many physiological functions, among which is the excretion of ammonia, the primary nitrogenous waste in most fishes. Although it is the end-product of nitrogen metabolism, ammonia serves many physiological functions including acting as an acid equivalent and as a counter-ion in mechanisms of ion regulation. Our current understanding of the mechanisms of ammonia excretion have been influenced by classic experimental work, clever mechanistic approaches, and modern molecular and genetic techniques. In this review, I will overview the history of the study of ammonia excretion by the gills of fishes, highlighting the important advancements that have shaped this field with a nearly 100-year history. The developmental and evolutionary implications of an ammonia and gill-dominated nitrogen regulation strategy in most fishes will also be discussed. Throughout the review, I point to areas in which more work is needed to push forward this field of research that continues to produce novel insights and discoveries that will undoubtedly shape our overall understanding of fish physiology.
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Affiliation(s)
- Alex M Zimmer
- Department of Biological Sciences, University of New Brunswick, 100 Tucker Park Road, Saint John, Saint John, New Brunswick, E2L 4L5, Canada.
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2
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Breves JP, Shaughnessy CA. Endocrine control of gill ionocyte function in euryhaline fishes. J Comp Physiol B 2024:10.1007/s00360-024-01555-3. [PMID: 38739280 DOI: 10.1007/s00360-024-01555-3] [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: 01/08/2024] [Revised: 02/16/2024] [Accepted: 04/11/2024] [Indexed: 05/14/2024]
Abstract
The endocrine system is an essential regulator of the osmoregulatory organs that enable euryhaline fishes to maintain hydromineral balance in a broad range of environmental salinities. Because branchial ionocytes are the primary site for the active exchange of Na+, Cl-, and Ca2+ with the external environment, their functional regulation is inextricably linked with adaptive responses to changes in salinity. Here, we review the molecular-level processes that connect osmoregulatory hormones with branchial ion transport. We focus on how factors such as prolactin, growth hormone, cortisol, and insulin-like growth-factors operate through their cognate receptors to direct the expression of specific ion transporters/channels, Na+/K+-ATPases, tight-junction proteins, and aquaporins in ion-absorptive (freshwater-type) and ion-secretory (seawater-type) ionocytes. While these connections have historically been deduced in teleost models, more recently, increased attention has been given to understanding the nature of these connections in basal lineages. We conclude our review by proposing areas for future investigation that aim to fill gaps in the collective understanding of how hormonal signaling underlies ionocyte-based processes.
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Affiliation(s)
- Jason P Breves
- Department of Biology, Skidmore College, 815 N. Broadway, Saratoga Springs, NY, 12866, USA.
| | - Ciaran A Shaughnessy
- Department of Integrative Biology, Oklahoma State University, 501 Life Sciences West, Stillwater, OK, 74078, USA
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Gonzalez RJ, Patrick ML, Val AL. Ion uptake in naturally acidic water. J Comp Physiol B 2024:10.1007/s00360-024-01552-6. [PMID: 38652292 DOI: 10.1007/s00360-024-01552-6] [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: 12/21/2023] [Revised: 03/14/2024] [Accepted: 03/30/2024] [Indexed: 04/25/2024]
Abstract
The first studies on ion regulation in fish exposed to low pH, which were inspired by the Acid Rain environmental crisis, seemed to indicate that ion transport at the gills was completely and irreversibly inhibited at pH 4.0-4.5 and below. However, work on characid fish native to the Rio Negro, a naturally acidic, blackwater tributary of the Amazon River, found that they possess ion transport mechanisms that are completely insensitive to pHs as low as 3.25. As more species were examined it appeared that pH-insensitive transport was a trait shared by many, if not most, species in the Order Characiformes. Subsequently, a few other species of fish have been shown to be able to transport ions at low pH, in particular zebrafish (Danio rerio), which show rapid recovery of Na+ uptake at pH 4.0 after initial inhibition. Measurements of rates of Na+ transport during exposure to pharmacological agents that inhibit various transport proteins suggested that characiform fish do not utilize the generally accepted mechanisms for Na+ transport that rely on some form of H+ extrusion. Examination of zebrafish transport at low pH suggest the rapid recovery may be due to a novel Na+/K+ exchanger, but after longer term exposure they may rely on a coupling of Na+/H+ exchangers and NH3 excretion. Further work is needed to clarify these mechanisms of transport and to find other acid-tolerant species to fully gain an appreciation of the diversity of physiological mechansisms involved.
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Affiliation(s)
- R J Gonzalez
- Department of Biology, University of San Diego, 5998 Alcalá Park, San Diego, CA, 92110, USA.
| | - M L Patrick
- Department of Biology, University of San Diego, 5998 Alcalá Park, San Diego, CA, 92110, USA
| | - A L Val
- Laboratório de Ecofisiologia E Evolução Molecular, Instituto Nacional de Pesquisas da Amazônia (INPA), Manaus, Amazonas, Brasil
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Shih SW, Yan JJ, Lu SW, Chuang YT, Lin HW, Chou MY, Hwang PP. Molecular Physiological Evidence for the Role of Na+-Cl− Co-Transporter in Branchial Na+ Uptake in Freshwater Teleosts. Int J Mol Sci 2023; 24:ijms24076597. [PMID: 37047570 PMCID: PMC10094795 DOI: 10.3390/ijms24076597] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2023] [Revised: 03/23/2023] [Accepted: 03/30/2023] [Indexed: 04/05/2023] Open
Abstract
The gills are the major organ for Na+ uptake in teleosts. It was proposed that freshwater (FW) teleosts adopt Na+/H+ exchanger 3 (Nhe3) as the primary transporter for Na+ uptake and Na+-Cl− co-transporter (Ncc) as the backup transporter. However, convincing molecular physiological evidence to support the role of Ncc in branchial Na+ uptake is still lacking due to the limitations of functional assays in the gills. Thus, this study aimed to reveal the role of branchial Ncc in Na+ uptake with an in vivo detection platform (scanning ion-selective electrode technique, SIET) that has been recently established in fish gills. First, we identified that Ncc2-expressing cells in zebrafish gills are a specific subtype of ionocyte (NCC ionocytes) by using single-cell transcriptome analysis and immunofluorescence. After a long-term low-Na+ FW exposure, zebrafish increased branchial Ncc2 expression and the number of NCC ionocytes and enhanced gill Na+ uptake capacity. Pharmacological treatments further suggested that Na+ is indeed taken up by Ncc, in addition to Nhe, in the gills. These findings reveal the uptake roles of both branchial Ncc and Nhe under FW and shed light on osmoregulatory physiology in adult fish.
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Affiliation(s)
- Shang-Wu Shih
- Institute of Cellular and Organismic Biology, Academia Sinica, Taipei 115201, Taiwan
- Department of Life Science, National Taiwan University, Taipei 106319, Taiwan
| | - Jia-Jiun Yan
- Institute of Cellular and Organismic Biology, Academia Sinica, Taipei 115201, Taiwan
| | - Shao-Wei Lu
- Institute of Cellular and Organismic Biology, Academia Sinica, Taipei 115201, Taiwan
| | - Ya-Ting Chuang
- Institute of Cellular and Organismic Biology, Academia Sinica, Taipei 115201, Taiwan
| | - How-Wei Lin
- Institute of Cellular and Organismic Biology, Academia Sinica, Taipei 115201, Taiwan
- Department of Bioscience and Biotechnology, National Taiwan Ocean University, Keelung 202301, Taiwan
| | - Ming-Yi Chou
- Department of Life Science, National Taiwan University, Taipei 106319, Taiwan
| | - Pung-Pung Hwang
- Institute of Cellular and Organismic Biology, Academia Sinica, Taipei 115201, Taiwan
- Department of Life Science, National Taiwan University, Taipei 106319, Taiwan
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Transcriptomic profile comparison reveals conservation of ionocytes across multiple organs. Sci Rep 2023; 13:3516. [PMID: 36864051 PMCID: PMC9981729 DOI: 10.1038/s41598-023-30603-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2022] [Accepted: 02/27/2023] [Indexed: 03/04/2023] Open
Abstract
Single-cell RNA sequencing has recently led to the identification of a flurry of rare, new cell types, such as the CFTR-high ionocytes in the airway epithelium. Ionocytes appear to be specifically responsible for fluid osmolarity and pH regulation. Similar cells exist in multiple other organs and have received various names, including intercalated cell in the kidney, mitochondria-rich cell in the inner ear, clear cell in the epididymis, and ionocyte in the salivary gland. Here, we compare the previously published transcriptomic profile of cells expressing FOXI1, the signature transcription factor expressed in airway ionocytes. Such FOXI1+ cells were found in datasets representing human and/or murine kidney, airway, epididymis, thymus, skin, inner ear, salivary gland, and prostate. This allowed us to assess the similarities between these cells and identify the core transcriptomic signature of this ionocyte 'family'. Our results demonstrate that, across all these organs, ionocytes maintain the expression of a characteristic set of genes, including FOXI1, KRT7, and ATP6V1B1. We conclude that the ionocyte signature defines a class of closely related cell types across multiple mammalian organs.
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Sadauskas-Henrique H, Smith DS, Val AL, Wood CM. Physicochemical properties of the dissolved organic carbon can lead to different physiological responses of zebrafish (Danio rerio) under neutral and acidic conditions. JOURNAL OF EXPERIMENTAL ZOOLOGY PART 2021; 335:864-878. [PMID: 34435751 DOI: 10.1002/jez.2537] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/03/2021] [Revised: 07/28/2021] [Accepted: 08/02/2021] [Indexed: 11/11/2022]
Abstract
Previous studies have suggested that the capacity of natural dissolved organic carbon (DOC) molecules to interact with biological membranes is associated with their aromaticity (SAC340 ); origin (allochthonous versus autochthonous, FI); molecular weight (Abs254/365 ); and relative fluorescence of DOC moieties (PARAFAC analysis). These interactions may be especially important when fish are challenged by acidic waters, which are known to inhibit the active uptake of Na+ and Cl- , while stimulating diffusive ion losses in freshwater fishes. Therefore, zebrafish were acclimated (7 days, pH 7.0) to five natural DOC sources (10 mg C/L), two from the Amazon Basin and three from Canada, together with a "no-added DOC" control. After the acclimation, fish were challenged by exposure to acidic water (pH 4.0) for 3 h. Osmoregulatory parameters were measured at pH 7.0 and 4.0. Acclimation to the five DOC sources did not disturb Na+ , Cl- and ammonia net fluxes, but resulted in differential elevations in Na+ , K+ ATPase and v-type H+ ATPase activities in fish at pH 7.0. However, after transfer to pH.4.0, the control fish exhibited rapid increases in both enzymes. In contrast the DOC- acclimated animals exhibited unchanged (Na+ , K+ ATPase) or differentially increased (v-type H+ ATPase) activities. Na+ , Cl- and ammonia net fluxes remained unchanged in the control fish, but were differentially elevated in most of the DOC treatments at pH 4.0, relative to the same DOC treatments at pH 7.0. Correlations between the osmoregulatory data the DOCs properties highlight that the DOC properties drive different effects on gill physiology.
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Affiliation(s)
- Helen Sadauskas-Henrique
- Laboratory of Ecophysiology and Molecular Evolution, Brazilian National Institute for Research of the Amazon, Manaus, AM, Brazil.,Universidade Santa Cecília (Unisanta), Santos, SP, Brazil
| | - D Scott Smith
- Department of Chemistry and Biochemistry, Wilfrid Laurier University, Waterloo, ON, Canada
| | - Adalberto L Val
- Laboratory of Ecophysiology and Molecular Evolution, Brazilian National Institute for Research of the Amazon, Manaus, AM, Brazil
| | - Chris M Wood
- Laboratory of Ecophysiology and Molecular Evolution, Brazilian National Institute for Research of the Amazon, Manaus, AM, Brazil.,Department of Zoology, University of British Columbia, Vancouver, BC, Canada
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