Previous in vitro studies have demonstrated that AQP1, traditionally viewed as a water channel, also facilitates the passage of CO2 and ammonia across cell membranes. This thesis summarizes the first in vivo studies confirming a physiologically-relevant role for AQP1 in acid-base balance and nitrogenous waste excretion. Zebrafish embryos were microinjected with a translation-blocking morpholino oligonucleotide targeted to the zebrafish AQP1 paralog, AQP1a. Closed-system respirometry, total CO2 analysis, tritiated water fluxes and measurement of ammonia excretion were performed on larvae at 4 days post-fertilization (dpf). Knockdown of AQP1a significantly reduced rates of water, CO2 and ammonia excretion. Use of phenylhydrazine, a haemolytic agent, provided evidence that the yolk sac epithelium AQP1a (and not erythrocyte AQP1a) is the major site of CO2 and ammonia movements. Further, the hypothesis that AQP1a and the Rh glycoprotein Rhcg1, another multi-functional gas channel, act in concert to regulate CO2 and ammonia excretion was explored. Exposure to conditions impairing ammonia excretion (such as high external ammonia (HEA) or alkaline water) modulated AQP1a protein expression in 4 dpf zebrafish larvae experiencing knockdown of Rhcg1. Chronic HEA exposure triggered a significant compensatory increase in AQP1a protein abundance in Rhcg1 morphants. Exposure of Rhcg1 morphants to pH 10 water, however, caused a significant decrease in AQP1a protein expression. Interestingly, when AQP1a mRNA and protein levels were examined in Rhcg1 morphants and vice versa, no changes were observed. Overall, zebrafish AQP1a was found to be a multi-functional transporter of water, CO2 and ammonia, though the exact relationship it holds with other such gas channels bears further exploration.

Previous in vitro studies have demonstrated that AQP1, traditionally viewed as a water channel, also facilitates the passage of CO2 and ammonia across cell membranes. This thesis summarizes the first in vivo studies confirming a physiologically-relevant role for AQP1 in acid-base balance and nitrogenous waste excretion. Zebrafish embryos were microinjected with a translation-blocking morpholino oligonucleotide targeted to the zebrafish AQP1 paralog, AQP1a. Closed-system respirometry, total CO2 analysis, tritiated water fluxes and measurement of ammonia excretion were performed on larvae at 4 days post-fertilization (dpf). Knockdown of AQP1a significantly reduced rates of water, CO2 and ammonia excretion. Use of phenylhydrazine, a haemolytic agent, provided evidence that the yolk sac epithelium AQP1a (and not erythrocyte AQP1a) is the major site of CO2 and ammonia movements. Further, the hypothesis that AQP1a and the Rh glycoprotein Rhcg1, another multi-functional gas channel, act in concert to regulate CO2 and ammonia excretion was explored. Exposure to conditions impairing ammonia excretion (such as high external ammonia (HEA) or alkaline water) modulated AQP1a protein expression in 4 dpf zebrafish larvae experiencing knockdown of Rhcg1. Chronic HEA exposure triggered a significant compensatory increase in AQP1a protein abundance in Rhcg1 morphants. Exposure of Rhcg1 morphants to pH 10 water, however, caused a significant decrease in AQP1a protein expression. Interestingly, when AQP1a mRNA and protein levels were examined in Rhcg1 morphants and vice versa, no changes were observed. Overall, zebrafish AQP1a was found to be a multi-functional transporter of water, CO2 and ammonia, though the exact relationship it holds with other such gas channels bears further exploration.

Water management is a serious issue that affects the performance and durability of PEM fuel cells. It is known, from previous experimental investigations, that surface wettability has influence on water behaviour and fuel cell performance. This finding has lead researchers to develop numerical tools for further investigation of the liquid water behaviour in gas channels. The Volume-of-Fluid (VOF) method has been used in a wide range of studies for its advantage of showing the multi-phase interface in a Computational Fluid Dynamics (CFD) simulation to understand liquid water behaviour in gas channels. In this thesis, numerical study has been carried out to examine the behaviour of liquid water in gas channels. The dynamic movement of the liquid water in the channel and the associated pressure drop, water saturation and water coverage of the GDL have been investigated. Firstly, flow diffusion into the GDL was examined to determine its effect on liquid droplet behaviour in a small section of a gas channel. Furthermore, the effects of the percentage of flow diffusion, GDL wettability, pore size, and water inlet velocity were investigated. Fluid diffusion into GDL found to have insignificant impact on liquid water behaviour so further investigations has been carried with a solid GDL surface. Secondly, gas channel geometry effect on liquid water behaviour was studied. Square, semicircle, triangle, trapezoid with a long base and trapezoid with a short base were compared to find suitable cross section geometry to carry wall wettability investigations. Among the examined geometries, the square cross section showed reasonable results for both scenarios of geometry design, fixed Reynolds number and fixed GDL interface. The effect of wall wettability was assessed by comparing nine different wall/GDL wettability combinations for straight and bend channels. Wall wettability found to have an impact on liquid water behaviour but not as much as GDL wettability. It affects liquid water saturation in the channel by a great deal by accumulating water in the channel edges affecting water behaviour. This was also proven in the last test case of a long channel where water accumulation was investigated by running the calculation until the percentage of water saturation is stabilized. It is also concluded that changing wall wettability from hydrophobic to hydrophilic doubles the percentage of channel occupied by liquid water and increases the time to reach steady state.