Browsing by Subject "Oxygen"
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Item Carbonic anhydrase function and evolution in the respiratory gas exchange system of marine fishes(2021-08-15) Dichiera, Angelina Maria; Esbaugh, Andrew; Thomas, Peter; Brandl, Simon J; Brauner, Colin JMany marine fishes have adaptive respiratory strategies to enable sufficient oxygen (O₂) uptake, as well as the excretion of metabolically-produced carbon dioxide (CO₂). A central figure in the intertwined systems of CO₂ excretion and tissue O₂ delivery is the metalloenzyme carbonic anhydrase (CA). In my dissertation I expand, and in some cases challenge, the classical role of CA in CO₂ excretion and its emerging role in tissue O₂ extraction in both the red blood cell (RBC) and tissue membranes. I investigated the role of RBC CA in a diverse group of fishes, and demonstrated basal fishes with a membrane-bound CA isoform in their gills (branchial CA-IV) possess a low-activity RBC CA. Using site-directed mutagenesis, I restored increased function to a basal fish RBC CA to demonstrate that a single amino acid is critical for CA function. Furthermore, phylogenetic analysis suggested high-activity RBC CA may have coevolved with enhanced hemoglobin (Hb) pH sensitivity in teleosts. I explored this relationship and demonstrated RBC CA activity dictated Hb-O₂ offloading rate in almost a 1:1 manner in red drum (Sciaenops ocellatus). RBC CA is best known for its role in CO₂ excretion so this study is the first to demonstrate RBC CA may be rate-limiting for O₂ offloading as well. An additional CA isoform has recently been implicated in tissue O₂ extraction: membrane-bound CA-IV found in the red muscle, heart, and eye. With the plethora of CA-IV isoforms that function in other physiological systems (e.g. acid-base and ion regulation), I sought to define which isoforms should be studied for respiration, using publicly available membrane-bound CA sequences for a comprehensive phylogeny, and paired with tissue distribution analyses. I demonstrated functional divergence in CA-IV isoforms in which some species possess multiple CA-IV isoforms for disparate physiological functions. This highlighted CA-IVa as the primary isoform to target for future respiratory gas exchange studies. Finally, I challenged fish with low O₂ exposure (hypoxia) to understand the role CA-IV may play under environmental stress, and in contribution to whole-animal performance. While fish did not recruit CA-IV under hypoxia acclimation as predicted, they maintained CA-IV protein synthesis to theoretically sustain tissue O₂ extraction. Furthermore, hypoxia acclimation improved swim performance under control conditions; however, anaerobic rather than aerobic processes seem to be driving this performance. Overall, my work presents critical information regarding the emerging roles of CA in tissue O₂ extraction in marine fishes, providing mechanistic and evolutionary insight on the enzyme’s function in respiratory gas exchange.Item Oxygen scavenging styrene-butadiene-styrene block copolymer films for barrier applications(2013-08) Tung, Kevin; Paul, Donald R.; Freeman, B. D. (Benny D.)This dissertation discusses the oxidation behavior of reactive membranes that were produced by solution casting and by melt extrusion. These films, containing styrene-butadiene-styrene (SBS) block copolymer that undergoes catalytic oxidation, are of potential use as an oxygen scavenging polymer (OSP) for barrier applications. A thin film kinetic model was developed to ascertain reaction parameters that were used to describe thick film oxidation behavior. Ultimately complex structures containing these scavengers need to be produced via melt-extrusion. Therefore, processing conditions were established to ensure that melt-processed films have the same oxidation kinetics and capacity as those prepared by solution casting. Blends containing a non-reactive styrene phase and an oxygen-scavenging SBS phase were extruded and, by uptake and permeation experiments, their oxidation behaviors were monitored. The flux behavior and time lag extension as a function of oxygen pressure, film thickness, SBS scavenger and photoinitator contents were measured and compared to the theoretical model. The permeation behavior of the reactive blend films containing SBS showed that time lags can be extended via an oxidative mechanism and barrier properties be improved compared to traditional packaging membrane of native polystyrene.Item Respiratory plasticity of red drum to chronic hypoxia(2022-12-01) Negrete, Benjamin Jr.; Esbaugh, Andrew; Thomas, Peter; Brandl, Simon J; Richards, Jeffrey GOcean deoxygenation (hypoxia) is a pressing concern in the face of climate change as hypoxic areas increase in size, duration, and magnitude with each year. When a fish cannot escape hypoxia, it must be able to make the appropriate physiological adjustments to maintain fitness. Juveniles and adults can display reversible phenotypic changes in low oxygen (O₂), while embryos and larvae may producing fixed traits that are carried to adulthood through developmental plasticity. Across all life stages aerobic metabolism is the most efficient way that fish generate energy, and the most impacted pathway under hypoxia. In my dissertation, I explore the flexible responses that compensate for changes to aerobic metabolism across different life stages of the marine teleost red drum (Sciaenops ocellatus) exposed to chronic, sub-lethal hypoxia. Hypoxia-acclimated juvenile drum demonstrated significant changes in hemoglobin (Hb) isoform expression relative to control. Changes in Hb expression co-occurred with reduced pH sensitivity, and increased O₂ binding affinity. Additionally, this correlated with increased maximum metabolic rate and aerobic scope relative to controls in hypoxia. These results demonstrate an important role for Hb isoforms in maximizing respiratory performance in hypoxia with implications at the whole-animal level. Furthermore, I investigated how acclimated fish respond to exhaustive exercise, and their anaerobic swim performance. I found that hypoxia-acclimated juveniles decreased ATP in the red muscle and increased ATP and glycolytic potential in their white muscle. This phenotype recruited white muscle at lower swim speeds than control fish, indicating a prioritization of glycolytic white muscle swimming over aerobic red muscle. Finally, I assess whole animal respiratory and swim performance in fish exposed to hypoxia during a critical window in early development. These fish show increases in aerobic performance in normoxia, while becoming more vulnerable to hypoxia in later life. I sought to understand the mechanisms and implications of hypoxia-induced respiratory adaptations, and demonstrated the ability of a marine fish to adapt to environmental stress, and how these adaptations changed in different life stages. This work demonstrates the species-specific resiliency and limitations in environmental stress, and illustrates the need for more species-specific work in a changing ocean.