Document Type

Thesis

Degree Name

Master of Science (MSc)

Department

Biology

Program Name/Specialization

Integrative Biology

Faculty/School

Faculty of Science

First Advisor

Jonathan Mark Wilson

Advisor Role

Supervisor

Abstract

The lungfish possesses a primitive lung and underdeveloped gills, making use of bimodal respiration. Like other freshwater fishes they must regulate ion- and acid-base equilibrium through active ion uptake (driven by pumps and ion transporters), albeit with challenges due to their underdeveloped gills. My thesis aimed to elucidate the role of the sodium proton exchangers (NHE), encoded by the genes slc9a1/nhe1, slc9a2/nhe2 and slc9a3/nhe3, which are hypothesized to contribute towards acid-base regulation. Pharmacologically, amiloride, a sodium-transport inhibitor, and 5-(N-Ethyl N-isopropyl)-Amiloride (EIPA), an NHE specific inhibitor, affected whole-animal titratable acidity and ammonia fluxes, supporting a physiological function of the NHE. Next, a PCR based approach was used that identified expression of all three NHE paralogues in both the gills and kidney. The function of NHE (and associated acid-base transporters) was assessed by challenging lungfish under acidic and basic extremes (of pH 4.0 and 9.0, respectively). After pH 9 acclimation, ammonia excretion transiently decreased and recovered. Gill nhe3 expression was upregulated, while kidney expression was unchanged. However, western blotting did not detect changes in NHE2 or NHE3 protein expression. Overall, my results suggest that nhe3 may be functioning as an Na+ /NH4 + exchanger under high pH conditions. The NHEs likely do not function under the low pH conditions, and changes in expression were not observed. Additional associated ion transporters were also examined. Rhesus glycoprotein C (rhcg), an ammonia gas channel, was downregulated in the gill suggesting an alternative method to nitrogenous waste excretion. The vacuolar proton pump expression also decreased at high pH. In conclusion this thesis finds that the NHEs are present in both acid-base and ionoregulatory organs of the lungfish providing a crucial link into our understanding the evolutionary transition from the aquatic to terrestrial environments in the lobe finned fishes.

Convocation Year

2026

Convocation Season

Spring

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Available for download on Tuesday, October 27, 2026

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