Dr Chris Glover - Research
Ion transport physiology
Ion homeostasis is perhaps the single most critical process ensuring the survival of osmoregulating aquatic animals. These organisms maintain their body ion concentrations at levels either significantly greater (in freshwater) or lower (in saltwater) than their surroundings. They are therefore constantly faced with diffusive ion loss or gain. To maintain body ion levels, and thus the optimal functioning of the cells and body systems that operate only in a narrow ionic concentration range, requires efficient mechanisms for ion excretion and absorption. Investigating these systems helps establish the capacity of aquatic organisms to survive in water of different salinities. It may also aid the understanding of factors such as sensitivity to waterborne contaminants, the ideal salinities for aquacultural rearing, natural habitat distribution, and can also provide insight into human diseases (e.g. cystic fibrosis). The remarkable capacity of some of these organisms to rapidly and comprehensively switch cellular physiology with changes in salinity remains to be adequately elucidated.
Investigating ion transport relies extensively on biochemical and physiological tools, such as enzyme assays and measurement of ion fluxes using radioisotopes. Increasingly molecular techniques, such as quantitative PCR are providing important insights.
Research in this area has previously included studies characterising sodium transport pathways in freshwater invertebrates, and the impacts of natural organic matter on ion transport. Ongoing work examining the ion transport capacities of inanga, an endemic amphidromous fish and component of the whitebait catch, is funded by the Royal Society’s Marsden Fund.
Selected references:
Glover, C.N. 2007. Cellular and molecular approaches to the investigation of piscine osmoregulation: current and future perspectives. In: Fish Osmoregulation (Eds. B.G. Kapoor, B. Baldisserotto, J. Mancera), Science Publishers Inc., Enfield, New Hampshire, pp. 177-234.
Glover, C.N. and Wood, C.M. 2005. Sodium metabolism disruption by humic substances in Daphnia magna: mechanistic investigation and effect of “real world” natural organic matter. Physiological and Biochemical Zoology, 78: 1005-1016.
Glover, C.N. and Wood, C.M. 2005. Physiological characterisation of a pH- and calcium-dependent sodium uptake mechanism in the freshwater crustacean, Daphnia magna. Journal of Experimental Biology, 208: 951-959.
Epithelial transport of toxicants and nutrients
To exert their beneficial or harmful effects on organisms, nutrients and toxicants must first traverse an epithelial surface (generally the gill or gut in aquatic animals). This process is one of the key regulatory points controlling eventual biological impact. As such it is often critical to understand absorption in order to understand nutrition and toxicity. Mechanistic knowledge of how nutrients are absorbed can ensure that optimal levels are delivered in diets, and that supplementation will not surreptitiously exclude the absorption of other vital nutrients that may share uptake pathways. Likewise, knowing mechanisms of toxicant transport can inform how absorption, and toxicity, will change in the presence of contaminant mixtures and in response to physiological acclimation. This approach has played a key role in the development of the latest environmental risk assessment tools for metals.
A number of in vivo and in vitro tools are utilised in the lab, including whole organ perfusion, isolated tissue preparations, and membrane vesicle approaches. These techniques often use the sensitivity of radiotracers, coupled with pharmacological agents to probe mechanisms of epithelial transport. Molecular characterisation of transporters can be used to lend structural support to the functional evidence gathered.
Transport of metals such as zinc and copper (both alone and in complexes with amino acids) across the intestinal surfaces of fish has been a major focus of past research. Absorption of amino acids in rainbow trout has also been examined.
Selected references:
Glover, C.N. and Wood, C.M. 2008. Histidine absorption across apical surfaces of freshwater rainbow trout intestine: mechanistic characterisation and the influence of copper. Journal of Membrane Biology, 221: 87-95.
Glover, C.N., Bury, N.R. and Hogstrand, C. 2003. Zinc uptake across the apical membrane of freshwater rainbow trout intestine is mediated by high affinity, low affinity and histidine-facilitated pathways. Biochimica et Biophysica Acta- Biomembranes, 1614: 211-219.
Bury, N.R., Walker, P.A. and Glover, C.N. 2003. Nutritive metal uptake in teleost fish. Journal of Experimental Biology, 206: 11-23.
Aquatic toxicology
Understanding the threat posed by pollutants in our waters is more complicated than it may initially appear. Factors such as water chemistry, contaminant speciation, concentration, routes of exposure (e.g. waterborne versus dietary), and a range of biological parameters (e.g. animal size, developmental stage, nutritional status, physiological processes, toxicological defences etc.) will all influence toxicological impact. For many aquatic toxicants we have a sound understanding of their mechanisms of action, and the roles these various factors may play in controlling their impact. For emerging contaminants (e.g. pharmaceuticals and nanoparticles) and pollutant mixtures we know very little. The sensitivity of New Zealand’s native fauna to aquatic toxicants is almost completely uncharacterised.
Research in this area takes a mechanistic approach, combining analytical chemistry, biogeochemical modelling, molecular biology, biochemistry, cell culture, physiology, behaviour and ecology to develop an understanding of how chemicals cause toxicity, and the risks they pose in the aquatic milieu.
Previous research in aquatic toxicology has included studies investigating the toxicity of dietary pesticides and metals to salmonid fish, toxicity of silver to freshwater invertebrates and the application of proteomic techniques to study toxicity in non-model species.
Selected references
Glover, C.N., Petri, D., Tollefsen, K.-E., Jørum, N., Handy, R.D. and Berntssen, M.H.G. 2007. Assessing sensitivity of Atlantic salmon (Salmo salar) to dietary endosulfan exposure using tissue biochemistry and histology. Aquatic Toxicology, 84: 367-378.
Glover, C.N., Playle, R.C. and Wood, C.M. 2005. Heterogeneity of natural organic matter amelioration of silver toxicity to Daphnia magna: effect of source and equilibration time. Environmental Toxicology and Chemistry, 24: 2934-2940.
Hogstrand, C., Balesaria, S. and Glover, C.N. 2002. Application of genomics and proteomics for study of the integrated response to zinc exposure in a non-model fish species, the rainbow trout. Comparative Biochemistry and Physiology B, 133: 523-535.
Seafood safety
Seafood is an important source of nutrients in the human diet, but may also contain contaminants with the potential to cause considerable harm. In recent years this has been an increasingly controversial area of research, with ongoing scientific debates regarding the risk posed by consuming methylmercury in fish during pregnancy, and the relative safety of cultured versus wild fish, for example. In many cases the toxicological impacts of seafood consumption may be offset by its nutritional benefits, but only rarely are both beneficial and harmful effects considered in risk assessment. Understanding the impact of seafood on the human consumer requires knowledge of the interactions between the varying chemical components of seafood. In addition knowledge of the transfer, metabolism, and fate of a contaminant as it traverses the lower levels of the food chain can provide critical information relevant to risk characterisation.
These investigations incorporate many of the standard biochemical and physiological techniques from mammalian and aquatic toxicology. Research in mammalian systems has, however, focussed on neurological impairment, and consequently neurobehavioural assessments feature prominently. Advances in the availability of large-scale gene expression screening technologies (microarrays) are also integrated into the research programme.
Research in this area has been performed in conjunction with colleagues at the National Institute of Nutrition and Seafood Research in Bergen, Norway and King’s College, London. It has included work examining the impacts of methylmercury in seafood on behaviour and neural gene expression in a mammalian model, and the potential for pesticides in aquacultural feeds to carry-over into the human food chain.
Selected references:
Glover, C.N., Zheng, D., Jayashankar, S., Sales, G.D., Hogstrand, C. and Lundebye, A.-K. Neural gene expression and neurobehavioural impacts of developmental methylmercury exposure in mice: effect of methylmercury speciation. In preparation.
Folven, K.I., Glover, C.N., Malde, M.K. and Lundebye, A.-K. Does selenium modify neurobehavioural impacts of developmental methylmercury exposure in mice? In review.
Berntssen, M.H.G., Glover, C.N., Robb, D.H.F., Jakobsen, J.-V. and Petri, D. 2008. Accumulation and elimination kinetics of dietary endosulfan in Atlantic salmon (Salmo salar). Aquatic Toxicology, 86: 104-111.