Homeostasis: Osmoregulation in elasmobranchs

1. Homeostasis: Osmoregulation in elasmobranchs The difference between marine, eurahyline and fresh water species

2. Osmoregulation • Relationship between solute to solvent concentrations of internal body fluids • The environment the organism lives in • Isotonic? • Hypertonic? • Hypotonic? Osmolarity = solute/solvent concentration

3. water molecules protein molecules semipermeable membrane between two compartments Fig. 5-20, p.86

4. 2% sucrose solution 1 liter of 10% sucrose solution 1 liter of 2% sucrose solution 1 liter of distilled water Hypotonic Conditions Hypertonic Conditions Isotonic Conditions Fig. 5-21, p.87

5. first compartment second compartment hypotonic solution hypertonic solution membrane permeable to water but not to solutions fluid volume rises in second compartment Fig. 5-22, p.87

6. Stepped Art Hypotonic Solution Hypertonic Solution membrane permeable to water but not to solutes Fig. 5-22, p.87

7. The Challenge • Avoid desiccation in an aqueous environment • MARINE ANIMALS • Dehydration • Elimination of excess salt • FRESHWATER ANIMALS • Conserve salts • Eliminate excess water

8. Environmental challenges of elasmobranchs • All ureotelic and ureosmotic except potamytrygonid rays • Marine elasmobranchs surrounded by salt; lose water; • need to get rid of excess organic and inorganic compounds • Euryhaline species environment fluctuates • Must handle salt and fresh conditions • Freshwater species • lose salt and electrolytes; need to get rid of excess water

9. Dealing with Environment • Marine : Maintain serum osmolarity = or greater than seawater primarily w/ urea • Little osmotic loss of water • Dilute Seawater or Freshwater: Serum osmolarity reduced • Little diffusion of water inward

10. Players in osmoregulation • Organs • Kidney, liver, gills, rectal gland • Organic compounds • Urea • TMAO trimethylamine oxide • Inorganic ions • Sodium • Chloride • Other salts

11. Umanitoba - Gary Anderson

12. Body FluidMarine Elasmobranchs • Reabsorb & retain urea and other body fluid solutes in tissues • Serum osmolarity remains just greater than external seawater (hyperosmotic) • Don’t have to drink water like teleosts • Water gained excreted by kidneys • Tri-MethylAmine Oxide (TMAO): Acts to counteract the perturbing effects of urea

13. Marine elasmobranchsPlasma solutes and osmoregulation • Different than marine teleosts • Have high osmolarity • Reabsorb and retain high levels of urea and TMAO in their body fluids • Osmolarity remains hyperosmotic to surrounding seawater • TMAO to stabilize proteins and activate enzymes • Water gained across gills is excreted by kidneys • Any salt gained across gills is excreted by rectal gland and kidney

14. Body fluid of euryhaline elasmobranchs • Ammonotelic in frehwater • As salinity increases • Increase urea production and retention • Decrease urea excretion • Increase Na+ and Cl- • Decrease ammonia excretion • Can not produce and retain as much urea as marine spp. (lower osmolarity) • Ex. D. sabina and H. signifier

15. Body fluid of euryhaline elasmobranchs As salinity decreases • Lower osmolarity (less urea and TMAO) than marine species • Decrease amount of urea produced and reabsorbed • Increased urinary excretion • Loss of sodium and chloride balanced by electrolyte uptake at the gills and reabsorbed by kidneys

16. Bull Shark - Carcharhinus leucas Eeigen Werk

17. Body FluidFresh Water Elasmobranchs • Lost ability to synthesize and retain urea or TMAO • Body fluid solute concentrations relatively low • Freshwater rays abandoned renal reabsorption • Urine is dilute • Ammonotelic • Ex. Potamotrygon rays

18. Potamotrygonidae Raimond Spekking

19. Urea- production, retention and reabsorption • Urea production • Occurs in the liver • Retention • In gills • Reabsorption • In kidneys

20. Urea production in liver Ornithine-urea cycle (OUC) • Glutamine synthetase is crucial enzyme needed for urea production • Euryhaline spp. decrease production of urea when entering fresh water • Freshwater rays lack the enzyme for the biosynthesis to occur • Unsure if urea is produced in other locations • Bacteria hypothesized for being responsible

21. Marine gills retain urea • Do not lose much urea across gills • Gill’s basolateral membrane has high cholesterol to phospholipid ratio levels • Membrane limit diffusion • Active transport of urea by Na+/ urea antiporter energized by Na+/K+ ATPases • Used more for salt regulation and acid/base balance

22. Kidneys reabsorb urea • Reabsorption contributes to high urea levels • Minor site of urea loss • Thought to involve active transport • Use urea-sodium pump • Proven in R. erinacea • Second hypothesis for passive transport that has not been proven • Euryhaline spp. decrease renal reabsorption of urea as enter areas of decreased salinity • Increases rate of urine flow to rid system of excess urea

23. Salt regulation • Rectal gland secretions • Marine spp. surrounded by high salinity • Rectal gland secretes sodium and chloride • Na+/ K+ ATPases used

24. Osmoregulation by the Rectal Gland • Rectal Gland = Salt secreting mechanism • Migratory elasmos - regressive rectal gland • Non-functional in freshwater rays http://fig.cox.miami.edu/~cmallery/150/physiol/rectal.htm

25. Salt regulation • Gills • Salt uptake • Na+/ K+ ATPases even higher in freshwater • Acid/ base balance • Secrete acid • H+ excreted/exchanged for Na+ • Run by Na+/ K+ ATPases • Responsible for ammmonia secretion

26. Salt regulation • Kidney salt excretion • Dilute environment • Urine flow increase • Saltwater • Not solely responsible for salt secretion

27. Endocrine Regulation to Regulate Body Fluid Volume and Solute Concentration • CNP - Released from heart • Increase urine production • Stimulate salt secretion from rectal gland • Inhibit drinking and relax blood vessels • AVT • Increase in plasma osmolality • Reduces urine production • RAS • Antagonistic to CNP, reduces urine flow • Increases drinking • Constricts blood vessels

28. Feeding and osmoregulation • Urea is metabolically expensive • 5 umol ATP for 1 mole urea • Protein in food is main source of N in urea • Elasmobranches must get adequate food to produce the urea • Why ureotelic and not ammonotelic???

29. Literture cited • Hammerschlag N.2006. Osmoregulation in elasmobranches: a review for fish biologists, behaviorists and ecologists.MARINE AND FRESHWATER BEHAVIOUR AND PHYSIOLOGY 39 (3): 209-228 • Speers-Roesch B, Ip YK, Ballantyne JS.2006. Metabolic organization of freshwater, euryhaline, and marine elasmobraches: implications for the evolution of energy metabolism insharks andrays. JOURNAL OF EXPERIMENTAL BIOLOGY 209 (13): 2495- 2508 • Pillans RD, Anderson WG, Good JP, et al.2006. Plasma and erythrocyte solute properties of juvenile bull sharks, Carcharhinus leucas, acutely exposed to increasing environmental salinity. JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY 331 (2): 145-157 • Pillans RD, Good JP, Anderson WG, et al. 2005.Freshwater to seawater acclimation of juvenile bull sharks (Carcharhinus leucas): plasma osmolytes and Na+/K+ ATPase activity in gill, rectal gland, kidney and intestine. JOURNAL OF COMPARATIVE PHYSIOLOGY B-BIOCHEMICAL SYSTEMIC AND ENVIRONMENTAL PHYSIOLOGY 175 (1): 37-44

30. Literature cited • Pillans RD, Franklin CE.2004. Plasma osmolyte concentrations and rectal gland mass of bull sharks Carcharhinus leucas, captured along a salinity gradient. COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY A- MOLECULAR & INTEGRATIVE PHYSIOLOGY 138 (3): 363-