UBC Theses and Dissertations
Patterns of plasma accessible carbonic anhydrase localisation in derived, basal, and developing fishes Nelson, Charlotte
Teleosts comprise half of all vertebrates and have successfully invaded every aquatic habitat on Earth. They owe this success, at least in part, to their unique oxygenation system. This system is comprised of highly pH sensitive hemoglobins (Hb; large Bohr and Root effects), red blood cell (RBC) intracellular pH (pHi) protection by a beta adrenergically stimulated sodium proton exchanger (β-NHE), and a heterogeneous distribution of plasma accessible carbonic anhydrase (paCA; absence at the gills and presence at the tissues). Together, these components enhance oxygen O₂ unloading to the tissues while protecting oxygen uptake at the gills during a generalised acidosis. While the first two components have received much research interest, the third component, a heterogeneous distribution of paCA, has not and is the focus of my thesis. It has been hypothesised that the absence of paCA in the gills of teleosts is due to the presence of the large Root effect and the associated risks to O₂ loading. In my thesis I aimed to address this principal hypothesis with three research chapters. I firstly confirmed the presence of paCA in most tissues, but absence in all four gill arches of the rainbow trout, which until now had been assumed to be true based on data exclusively from gill arch 2. I then investigated rainbow trout through ontogeny, and found that pre-hatch, during embryonic Hb expression branchial paCA is expressed while β-NHE is not; a pattern that exhibits an abrupt switch with hatching. Finally, I investigated several CA characteristics in three basal actinopterygian species for which nothing was known previously. I demonstrated that paCA in the gill was likely lost earlier than predicted by my principal hypothesis, suggesting instead that the loss of branchial paCA is related to the increasing magnitude of the Bohr coefficient and corresponding decrease in Hb buffer capacity. Collectively, my findings suggest that the presence of a large Root effect is unlikely to be the single selective factor for the loss of branchial paCA in teleosts, with implications for our understanding of a group that represents half of all vertebrates.
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