Author
James S. Ballantyne
Other affiliations: University of St Andrews, University of Ottawa
Bio: James S. Ballantyne is an academic researcher from University of Guelph. The author has contributed to research in topics: Urea & Na+/K+-ATPase. The author has an hindex of 34, co-authored 112 publications receiving 3666 citations. Previous affiliations of James S. Ballantyne include University of St Andrews & University of Ottawa.
Topics: Urea, Na+/K+-ATPase, Glutamine, Lipid oxidation, Fatty acid
Papers published on a yearly basis
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TL;DR: The reciprocal expression of Na+/K+-ATPase isoforms α1a and α1b during seawater acclimation suggests they may have different roles in the gills of freshwater and marine fishes; ion uptake in freshwater fish and ion secretion in marine fishes.
Abstract: The upregulation of gill Na+/K+-ATPase activity is considered critical for the successful acclimation of salmonid fishes to seawater. The present study examines the mRNA expression of two recently discovered alpha-subunit isoforms of Na+/K+-ATPase (alpha1a and alpha1b) in gill during the seawater acclimation of three species of anadromous salmonids, which vary in their salinity tolerance. Levels of these Na+/K+-ATPase isoforms were compared with Na+/K+-ATPase activity and protein abundance and related to the seawater tolerance of each species. Atlantic salmon (Salmo salar) quickly regulated plasma Na+, Cl- and osmolality levels within 10 days of seawater exposure, whereas rainbow trout (Oncorhynchus mykiss) and Arctic char (Salvelinus alpinus) struggled to ionoregulate, and experienced greater perturbations in plasma ion levels for a longer period of time. In all three species, mRNA levels for the alpha1a isoform quickly decreased following seawater exposure whereas alpha1b levels increased significantly. All three species displayed similar increases in gill Na+/K+-ATPase activity during seawater acclimation, with levels rising after 10 and 30 days. Freshwater Atlantic salmon gill Na+/K+-ATPase activity and protein content was threefold higher than those of Arctic char and rainbow trout, which may explain their superior seawater tolerance. The role of the alpha1b isoform may be of particular importance during seawater acclimation of salmonid fishes. The reciprocal expression of Na+/K+-ATPase isoforms alpha1a and alpha1b during seawater acclimation suggests they may have different roles in the gills of freshwater and marine fishes; ion uptake in freshwater fish and ion secretion in marine fishes.
194 citations
TL;DR: The reduced availability of glutamine coupled with the low levels of nonesterified fatty acids in the blood reduces the availability of molecules essential for tumor growth, which may provide marine elasmobranchs with a “systemic” resistance to cancer.
Abstract: Elasmobranchs are of metabolic interest for several reasons, including their primitive evolutionary position, their osmotic strategy and their low incidence of neoplasia. Some aspects of the metabolism of elasmobranch fishes are unique when compared with those of the other vertebrates. Although many features of their metabolism can be attributed to their primitive evolutionary position (e.g., fewer isoforms of enzymes and other proteins), some unique features appear to be related to the unusual solute system (urea and methylamines) used by elasmobranchs. The solute system exerts widespread effects, which has an impact on the metabolism of lipids, ketone bodies and amino acids and the structure of proteins and membranes. Effects of urea on the transport of lipid may influence aspects of lipid metabolism, reducing extrahepatic lipid catabolism via effects on nonesterified fatty acid transport and enhancing a need for reliance on ketone bodies. Amino acid metabolism of elasmobranchs is also heavily influenced by the need for continuous synthesis of urea with glutamine as the nitrogen donor. These effects, in turn, may play a role in their low incidence of cancer. Specifically, the reduced availability of glutamine (an important nutrient for rapidly growing cells) coupled with the low levels of nonesterified fatty acids in the blood reduces the availability of molecules essential for tumor growth. This metabolic design may thus provide marine elasmobranchs with a “systemic” resistance to cancer.
191 citations
TL;DR: It is suggested that high stocking density has the effect of mobilizing triglyceride sources, promoting gluconeogenesis from glycerol, but has little effect on protein metabolism.
170 citations
TL;DR: Cortisol was administered to brook charr (Salvelinus fontinalis) in the form of slow-release intraperitoneal implants to investigate the effect of chronic cortisol stimulation (up to 60 days) on various aspects of intermediary metabolism, and to determine whether such cortisol-induced changes were comparable to those seen in chronically fasted charr as mentioned in this paper.
128 citations
TL;DR: This work proposes that a unique combination of active urea transport and modification of the phospholipid bilayer membrane is responsible for decreasing the gill permeability to urea and facilitating urea retention by the gills of Squalus acanthias.
Abstract: In elasmobranch fishes, urea occurs at high concentrations (350–600 mM) in the body fluids and tissues, where it plays an important role in osmoregulation. Retention of urea by the gill against thi...
126 citations
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TL;DR: The mechanism of mitochondrial RIRR highlights the central role of mitochondria-formed ROS, and all of the known ROS-producing sites and their relevance to the mitochondrial ROS production in vivo are discussed.
Abstract: Byproducts of normal mitochondrial metabolism and homeostasis include the buildup of potentially damaging levels of reactive oxygen species (ROS), Ca2+, etc., which must be normalized. Evidence suggests that brief mitochondrial permeability transition pore (mPTP) openings play an important physiological role maintaining healthy mitochondria homeostasis. Adaptive and maladaptive responses to redox stress may involve mitochondrial channels such as mPTP and inner membrane anion channel (IMAC). Their activation causes intra- and intermitochondrial redox-environment changes leading to ROS release. This regenerative cycle of mitochondrial ROS formation and release was named ROS-induced ROS release (RIRR). Brief, reversible mPTP opening-associated ROS release apparently constitutes an adaptive housekeeping function by the timely release from mitochondria of accumulated potentially toxic levels of ROS (and Ca2+). At higher ROS levels, longer mPTP openings may release a ROS burst leading to destruction of mitochondria, and if propagated from mitochondrion to mitochondrion, of the cell itself. The destructive function of RIRR may serve a physiological role by removal of unwanted cells or damaged mitochondria, or cause the pathological elimination of vital and essential mitochondria and cells. The adaptive release of sufficient ROS into the vicinity of mitochondria may also activate local pools of redox-sensitive enzymes involved in protective signaling pathways that limit ischemic damage to mitochondria and cells in that area. Maladaptive mPTP- or IMAC-related RIRR may also be playing a role in aging. Because the mechanism of mitochondrial RIRR highlights the central role of mitochondria-formed ROS, we discuss all of the known ROS-producing sites (shown in vitro) and their relevance to the mitochondrial ROS production in vivo.
2,893 citations
TL;DR: The fish gill is a multipurpose organ that, in addition to providing for aquatic gas exchange, plays dominant roles in osmotic and ionic regulation, acid-base regulation, and excretion of nitrogenous wastes.
Abstract: The fish gill is a multipurpose organ that, in addition to providing for aquatic gas exchange, plays dominant roles in osmotic and ionic regulation, acid-base regulation, and excretion of nitrogenous wastes Thus, despite the fact that all fish groups have functional kidneys, the gill epithelium is the site of many processes that are mediated by renal epithelia in terrestrial vertebrates Indeed, many of the pathways that mediate these processes in mammalian renal epithelial are expressed in the gill, and many of the extrinsic and intrinsic modulators of these processes are also found in fish endocrine tissues and the gill itself The basic patterns of gill physiology were outlined over a half century ago, but modern immunological and molecular techniques are bringing new insights into this complicated system Nevertheless, substantial questions about the evolution of these mechanisms and control remain
2,371 citations
TL;DR: This review attempts to delineate common themes on the physiological and metabolic roles of cortisol in teleost fishes and to suggest new approaches that might overcome some of the inconsistencies on the role of this multifaceted hormone.
Abstract: Cortisol is the principal corticosteriod in teleost fishes and its plasma concentrations rise dramatically during stress. The relationship between this cortisol increase and its metabolic consequences are subject to extensive debate. Much of this debate arises from the different responses of the many species used, the diversity of approaches to manipulate cortisol levels, and the sampling techniques and duration. Given the extreme differences in experimental approach, it is not surprising that inconsistencies exist within the literature. This review attempts to delineate common themes on the physiological and metabolic roles of cortisol in teleost fishes and to suggest new approaches that might overcome some of the inconsistencies on the role of this multifaceted hormone. We detail the dynamics of cortisol, especially the exogenous and endogenous factors modulating production, clearance and tissue availability of the hormone. We focus on the mechanisms of action, the biochemical and physiological impact, and the interaction with other hormones so as to provide a conceptual framework for cortisol under resting and/or stressed states. Interpretation of interactions between cortisol and other glucoregulatory hormones is hampered by the absence of adequate hormone quantification, resulting in correlative rather than causal relationships.
2,139 citations
TL;DR: Fish have strategies to protect them from the ammonia pulse following feeding, and this also protects them from increases in external ammonia, as a result starved fish are more sensitive to external ammonia than fed fish.
856 citations
855 citations