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Harter TS, Smith EA, Salmerón C, Thies AB, Delgado B, Wilson RW, Tresguerres M. Soluble adenylyl cyclase is an acid-base sensor in rainbow trout red blood cells that regulates intracellular pH and haemoglobin-oxygen binding. Acta Physiol (Oxf) 2024; 240:e14205. [PMID: 39031444 DOI: 10.1111/apha.14205] [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: 02/12/2024] [Revised: 06/12/2024] [Accepted: 07/04/2024] [Indexed: 07/22/2024]
Abstract
AIM To identify the physiological role of the acid-base sensing enzyme, soluble adenylyl cyclase (sAC), in red blood cells (RBC) of the model teleost fish, rainbow trout. METHODS We used: (i) super-resolution microscopy to determine the subcellular location of sAC protein; (ii) live-cell imaging of RBC intracellular pH (pHi) with specific sAC inhibition (KH7 or LRE1) to determine its role in cellular acid-base regulation; (iii) spectrophotometric measurements of haemoglobin-oxygen (Hb-O2) binding in steady-state conditions; and (iv) during simulated arterial-venous transit, to determine the role of sAC in systemic O2 transport. RESULTS Distinct pools of sAC protein were detected in the RBC cytoplasm, at the plasma membrane and within the nucleus. Inhibition of sAC decreased the setpoint for RBC pHi regulation by ~0.25 pH units compared to controls, and slowed the rates of RBC pHi recovery after an acid-base disturbance. RBC pHi recovery was entirely through the anion exchanger (AE) that was in part regulated by HCO3 --dependent sAC signaling. Inhibition of sAC decreased Hb-O2 affinity during a respiratory acidosis compared to controls and reduced the cooperativity of O2 binding. During in vitro simulations of arterial-venous transit, sAC inhibition decreased the amount of O2 that is unloaded by ~11%. CONCLUSION sAC represents a novel acid-base sensor in the RBCs of rainbow trout, where it participates in the modulation of RBC pHi and blood O2 transport though the regulation of AE activity. If substantiated in other species, these findings may have broad implications for our understanding of cardiovascular physiology in vertebrates.
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Affiliation(s)
- Till S Harter
- Marine Biology Research Division, Scripps Institution of Oceanography, University of California San Diego, La Jolla, California, USA
| | - Emma A Smith
- Marine Biology Research Division, Scripps Institution of Oceanography, University of California San Diego, La Jolla, California, USA
| | - Cristina Salmerón
- Department of Pharmacology, University of California San Diego, La Jolla, California, USA
| | - Angus B Thies
- Marine Biology Research Division, Scripps Institution of Oceanography, University of California San Diego, La Jolla, California, USA
| | - Bryan Delgado
- Marine Biology Research Division, Scripps Institution of Oceanography, University of California San Diego, La Jolla, California, USA
| | - Rod W Wilson
- Biosciences Department, College of Life and Environmental Sciences, University of Exeter, Exeter, UK
| | - Martin Tresguerres
- Marine Biology Research Division, Scripps Institution of Oceanography, University of California San Diego, La Jolla, California, USA
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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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Montgomery DW, Kwan GT, Davison WG, Finlay J, Berry A, Simpson SD, Engelhard GH, Birchenough SNR, Tresguerres M, Wilson RW. Rapid blood acid-base regulation by European sea bass (Dicentrarchus labrax) in response to sudden exposure to high environmental CO2. J Exp Biol 2022; 225:jeb242735. [PMID: 35005768 PMCID: PMC8917447 DOI: 10.1242/jeb.242735] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2021] [Accepted: 12/20/2021] [Indexed: 11/22/2022]
Abstract
Fish in coastal ecosystems can be exposed to acute variations in CO2 of between 0.2 and 1 kPa CO2 (2000-10,000 µatm). Coping with this environmental challenge will depend on the ability to rapidly compensate for the internal acid-base disturbance caused by sudden exposure to high environmental CO2 (blood and tissue acidosis); however, studies about the speed of acid-base regulatory responses in marine fish are scarce. We observed that upon sudden exposure to ∼1 kPa CO2, European sea bass (Dicentrarchus labrax) completely regulate erythrocyte intracellular pH within ∼40 min, thus restoring haemoglobin-O2 affinity to pre-exposure levels. Moreover, blood pH returned to normal levels within ∼2 h, which is one of the fastest acid-base recoveries documented in any fish. This was achieved via a large upregulation of net acid excretion and accumulation of HCO3- in blood, which increased from ∼4 to ∼22 mmol l-1. While the abundance and intracellular localisation of gill Na+/K+-ATPase (NKA) and Na+/H+ exchanger 3 (NHE3) remained unchanged, the apical surface area of acid-excreting gill ionocytes doubled. This constitutes a novel mechanism for rapidly increasing acid excretion during sudden blood acidosis. Rapid acid-base regulation was completely prevented when the same high CO2 exposure occurred in seawater with experimentally reduced HCO3- and pH, probably because reduced environmental pH inhibited gill H+ excretion via NHE3. The rapid and robust acid-base regulatory responses identified will enable European sea bass to maintain physiological performance during large and sudden CO2 fluctuations that naturally occur in coastal environments.
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Affiliation(s)
| | - Garfield T. Kwan
- Marine Biology Research Division, Scripps Institution of Oceanography, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA
- National Oceanic and Atmospheric Administration Fisheries Service, Southwest Fisheries Science Center, 8901 La Jolla Shores Drive, La Jolla, CA 92037, USA
| | - William G. Davison
- Biosciences, Geoffrey Pope Building, University of Exeter, Exeter, EX4 4QD, UK
| | - Jennifer Finlay
- Biosciences, Geoffrey Pope Building, University of Exeter, Exeter, EX4 4QD, UK
| | - Alex Berry
- Biosciences, Geoffrey Pope Building, University of Exeter, Exeter, EX4 4QD, UK
| | - Stephen D. Simpson
- Biosciences, Geoffrey Pope Building, University of Exeter, Exeter, EX4 4QD, UK
| | - Georg H. Engelhard
- Centre for Environment, Fisheries & Aquaculture Science (Cefas), Pakefield Road, Lowestoft, NR330HT, UK
- School of Environmental Sciences, University of East Anglia, Norwich, NR4 7TJ, UK
| | - Silvana N. R. Birchenough
- Centre for Environment, Fisheries & Aquaculture Science (Cefas), Pakefield Road, Lowestoft, NR330HT, UK
| | - Martin Tresguerres
- Marine Biology Research Division, Scripps Institution of Oceanography, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA
| | - Rod W. Wilson
- Biosciences, Geoffrey Pope Building, University of Exeter, Exeter, EX4 4QD, UK
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