BI451 Lecture 11 Osmoregulation F23.pptx

BI451 Osmoregulation and Ion Balance in the Fishes. CH6 OUTLINE Properties of Water and Osmosis Homeostasis Living in Fresh water (hyperosmotic regulation) Living in Sea water (hypo-osmotic regulation) Agnathans, elasmobranches and teleosts Euryhaline fishes-eel example Evolutionary patterns of o...

BI451 Osmoregulation and Ion Balance in the Fishes. CH6 OUTLINE Properties of Water and Osmosis Homeostasis Living in Fresh water (hyperosmotic regulation) Living in Sea water (hypo-osmotic regulation) Agnathans, elasmobranches and teleosts Euryhaline fishes-eel example Evolutionary patterns of osmoregulation Summary I. Properties of Natural Waters SALINITY = grams inorganic matter per kg water = g/kg = ppt (parts per thousand) • freshwater FW = 0.1 to 0.2 ppt • saltwater SW = 34-37 ppt • hypersaline water HSW = >40 ppt • Brackish water BW = 0.5 to 30 ppt • Inland Saline Lakes 6 up to 200 ppt (e.g. Great Salt Lake, Dead Sea) Table 1: Ion Concentration (mmol·L-1) of Natural Fresh Salt Waters [Na+] [Cl-] [Mg2+] [SO42-] [Ca2+] [K+] [HCO3-] Water Water 0.35 0.23 0.21 0.19 0.75 0.08 1.7 470 mM 548 54 28 10 10 10 Osmolality 0.5 – 10 1050 mosM(per kg water) Osmosis (refresher slide) REVIEW II. Maintaining Homeostasis in Aquatic Environments 1. Osmoregulation • Maintenance of osmolarity within body's normal operating limits. 2. Ionoregulation • Closely linked because ion are osmolytes • Control of internal ion concentrations in body fluids • May be specific to the type of ion (eg. Ca2+) III. Strategies to Cope with Different Water Compositions (i) Osmoconformer: body fluid osmotic pressure changes with medium (ii) Osmoregulator: regulate internal osmotic concentrations (iii) Ionic Regulation: control body fluid solute Composition & Osmolarity in Fis Hagfish and elasmobranches: Lamprey and teleosts: All freshwater animals: IV. Fresh Water Hyperosmoregulation Challenges • Bony Fishes & Lampreys • Diffusional salt loss across body surface » Mainly Gills • Osmotic water influx • Incidental water influx during feeding Fig 8-3. Hill & Wyse 1989. Solutions Strategies of IonOsmoregulation in Freshwater Fishes 1. DO NOT DRINK 2. Highly Impermeable Tegument (skin) » deep tight junctions make gill less ion permeable 3. Produce Copious Dilute Urine (kidney = "bilge pump") 4. Active Ion Uptake Via Gills • Freshwater ionocytes (ion transport cells) and Vertebrate Kidney Design (Mammalian kidney: produces concentrated urine) Glomerular Filtration Na+, Cl- Re-uptake Water Re-uptake Excretion Loop of Henle with collecting tubule concentrates filtrate but lacking in fishes reshwater Kidney - “Bilge Pump” • Lampreys & bony fishes • Glomerular kidney » high glomerular filtration rate (GFR) & urinary flow rate(UFR) • High rate of Na+, Cl- reabsorption at Proximal (PT) & Distal Tubules (DT) • Little water reabsorption at underdeveloped/absent intermediate segment (IS) and at collecting tubule (CT) Ion movements across membranes REVIEW The charge (+/-) on ions makes it difficult for them to cross membranes Carrier (ATPases, symporters, or antiporters) or channel proteins are used. Movement against (electro)chemical gradients Energy (ATP) Coupled transport symport Ext antiport Int Ext Int > > < Freshwater Ionocytes Fresh Water • low Na+, Cl-, K+ • variable Ca2+ Blood • high Na+, Cl• low K+, Ca2+ Na+ and H + exchange (direct or indirect) or Cl - and HCO3 – exchange. H + and HCO – are acid-base equivalents providing onnection to Acid-base regulatio CA CA CA Na + /H+ exchange: Na + uptake for H + or acid excretion. Direct or indirect coupling. Cl-/HCO3- exchange: Cl- uptake for HCO3- or base excretion Carbonic anhydrase (CA) provides H+ and HCO3from CO2 hydration reaction Scanning & Transmission Electron Micrographs Showing Ionocytes in Fundulus heteroclitus Sea Water Fresh Water Ionocytes: n & Osmoregulation in Marine Fis Challenges: • Diffusional salt influx across body surface • Osmotic water loss • Salt influx during feeding • Entry of Toxic Divalents (Mg2+, SO42-, Ca2+) Compensation: Strategies of Ion & Osmoregulation in 1. Osmoconformer Marine FishesGlomerular kidney • Hagfish • blood isosmotic with seawater • Mesonephric Kidney » urine blood composition » Mg2+, SO42-, Ca2+, PO42- in glomerular filtrate • Ionic Secretions in Slime » high Na+, Mg2+, SO42-, K+ • Ionocytes in gills » H+ & HCO3- excretion (acidbase regulation) but not NaCl 2. Elasmobranchs Osmoconforming ionregulators Slightly hyperosmotic but hypoionic to seawater Hill and Wyse 1989. Three Major Strategies Retention sites (i) Retain Solutes (e.g. Urea, TMAO) Why? Ureosmoregulation • High [Urea] 100 times greater than in mammals • Slight, inwardly directed osmotic gradient • TMAO retained as a counterbalancing solute Gill • low urea permeability (Boylan. 1967) » 1/50 to 1/100 less permeable than trout gill • active urea transport (Fines et al. 2000). • de novo urea synthesis in gill (Wood et al. 1995)? Kidney • active urea transporters Mechanisms of Urea Retention in Elasmobranchs Gill and kidney are designed to retain urea. FYI Mechanisms of Urea Retention in Elasmobranchs • Urea Reabsorption (Goldstein & Forster 1971) » Na+:Urea Co-transport (Schmidt-Nielsen et al. 1972) » Phoretin blocks urea re-uptake (Hays et al. 1977) » Shark UT cloned (Smith & Wright 1999) » counter current bundle However, kidney Urea 2. Elasmobranchs continued... (ii) Do NOT Drink (iii) Special salt secreting gland: Active Na+Cl- Excretion by Rectal Gland Rectal Gland Secretions • [Na+] & [Cl-] » approximates SW » 2 times plasma • NaCl secretion stimulated by ANP Atrial Natriuretic Peptide Coelacanth • approximately isosmotic to Sea Water • urea & TMAO retention » mechanisms unknown » plasma ion levels less than in Sea Water • rectal gland » function unknown although high NKA activity like shark rectal gland. So presumably NaCl secretion. n & Osmoregulation in Marine Fis Challenges: • Diffusional salt influx across body surface • Osmotic water loss • Salt influx during feeding • Entry of Toxic Divalents (Mg2+, SO42-, Ca2+) Compensation: 3. Marine Teleosts and Lampreys - Hyposmoregulators Strategies (i) Impermeable Tegument (ii) Drink Salt Water » active absorption of ions & water across gut (iii) Active Na+ & Cl- extrusion via Saltwater ionocytes (Chloride Cells) » shallow tight junctions » deep apical crypt » associated with accessory cells (iv) Kidney's Role limited to excretion of toxic divalents (e.g. Mg2+, Ca2+, SO42-) 3ii. Drinking saltwater i) Imbibed SW is desalinated in esophagus (and stomach). NaCl but not water transport. ii) Water entering the intestine is now iso-osmotic with blood. Absorption of NaCl carries water with it. iii) Ca2+ and Mg2+ in imbibed SW is not absorbed but precipitated by secreted HCO3- as carbonates CaCO3 and MgCO3 Drinking saltwater adds to salt 3ii. Drinking saltwater. Divalent cations. Carbonates in fish poop important in marine carbon cycle (Wilson et al. 2009 Science) X-ray of flounder Carbonate precipitates Saltwater Ionocyte (Chloride Cel Salt Water • very high Na+, Cl• Mg2+, SO42-, Ca2+ Blood • high Na+, Cl• low K+, Ca2+ Saltwater Ionocyte (Chloride Cel MRC (CC): AC: 3iv. Kidney Excretes Small Amounts of Concentrated Urine in Sea Water Fishes → water conservation • Aglomerular (lost glomeruli) & Glomerular • Low rate of glomerular filtration & urine flow • Lower Na+, Cl- reabsorption » loss of intermediary & distal tubule in many fishes • Not designed for water reabsorption • Main role excretion of toxic divalents (Mg2+, SO42-, Ca2+) VI. Euryhaline Fishes • Euryhaline (< 1% of species) » broad salinity tolerance (SW to FW) » lampreys, Atlantic stingrays, bull sharks, sturgeon, killifishes, salmon, eels, shad, alewife (gaspereau), striped bass, flounder, some tilapia species • Catadromous » migrate down rivers as adults to spawn in the sea and juveniles back to fresh water to grow » Eels • Anadromous » migrate up rivers as adults to spawn and juveniles downstream to the sea to grow. » Salmon and sea lamprey VI. Euryhaline Fishes asion of Fresh Water from Salt W ancestor R.W. Griffith Ancestral marine jawless fish • Migration between fresh & salt water • Fresh water provided refuge for larvae • Fresh water nutrient poor Lutz 1975 Copeia SW FW Marine Origins of the Vertebrates Arguments for fw origin: glomerular kidney. However: (i) High Pressure Filtration Kidney needed for processing N-wastes (ii) Filtration kidney not restricted to vertebrates » crustaceans have marine origin (iii) Hagfish are osmoconformers » filtration kidney ALSO: Fossil record indicates marine origin » Haikouichthys sp. - early Cambrian (~520 mya) SW FW 5 mm Holland & Chen 2003. BioEssays 23:142. Lower Osmolarity & Ion Concentrations Retained After Re-Invasion of Salt in of Vertebrates r Osmolarity Water & Salinity Body Fluids s for Osmoregulation & Ion Balance Lampreys, Bony Fishes neys form Concentrated Urine Very Long Loops of Henle in Cetaceans t Secreting Glands Elasmobranch - Rectal Gland Birds & Reptiles – Nasal/lingual Salt Glands Coral catfish - Dendritic organ Retention for Osmoregulation Elasmobranchs & Coelancanths isosmotic” SW FW Summary Freshwater Fishes • hyperosmotic regulators » excrete copious, dilute urine » ion uptake cells in gills. Saltwater Fishes • isosmotic » hagfish = osmoconformers » elasmobranchs = isosmotic but hypoionic - urea/TMAO - rectal gland • hyposmotic regulators » lampreys, teleosts »SW MR cells (ion excretory) Euryhaline Salmonids • reciprocal regulation of ion transport Evolutionary patterns in osmoregulation in fishes