title: Some of the most interesting things we know, and don't know, about the biochemistry and physiology of elasmobranch fishes (sharks, skates and rays).
abstract: The urea-retaining strategy of elasmobranchs has shaped their biochemistry and physiology; from their metabolic organization to the structure of their membranes. It has also affected their capacity to live in freshwater. Although much new information has been uncovered in the past 30years, many unanswered questions remain. These include: a) why was urea selected as the major organic osmolyte, b) why is glutamine used as a nitrogen donor, c) why was plasma albumin lost in marine elasmobranchs, d) what membranes are involved in urea retention in the gills, e) how do urea and trimethylamine N-oxide (TMAO) affect membranes, and f) why retain urea in freshwater. Hypotheses are presented for future investigations but some questions may require a time machine to answer.
authors.affiliation: Department of Integrative Biology, University of Guelph, Guelph, ON N1G 2W1, Canada. Electronic address: jballant@uoguelph.ca.
authors.forename: James S
authors.initials: JS
authors.lastname: Ballantyne
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D018940:Elasmobranchii / Q000378:metabolism* / Q000502:physiology; D005618:Fresh Water; D012754:Sharks / Q000378:metabolism / Q000502:physiology; D012860:Skates, Fish / Q000378:metabolism / Q000502:physiology; D014508:Urea / Q000378:metabolism
chemical_list: D014508:Urea