Osmoregulation in MarineTeleosts

Cl- cells

Image credit: cornell.edu; Karnaky 1986

amazon.co.uk

Image credit: amazon.com

Osmoregulation:

• Regulation of osmotic pressure of internal fluids

Osmoregulation:

• Regulation of osmotic pressure of internal fluids• Osmosis

Osmoregulation:

• Regulation of osmotic pressure of internal fluids• Osmosis• Excretion, ingestion, absorption

Three common marine strategies:

1. Osmoconform• Agnathan hagfish & many marine invertebrates• Conform internal [ion] to [external medium]

Three common marine strategies:

1. Osmoconform• Agnathan hagfish & many marine invertebrates• Conform internal [ion] to [external medium]• Evidence of marine origin for vertebrate life?

Image credit: hawaiianatolls.org ; sagepub.com

Image credit: templecuttingedge.files.wordpress.com; abdn.ac.uk; sagepub.com

Three common marine strategies:

2. Osmoconform and ion regulate• Sharks, coelacanth and some amphibians• Plasma concentrations > seawater• NaCl concentration ~ 1/3 seawater

Three common marine strategies:

2. Osmoconform and ion regulate• Sharks• Plasma concentrations > seawater • NaCl concentration ~1/3 seawater• Urea & Trimethylamine N-oxidase (TMAO)• Internal fluids ~5% saltier than seawater

Image credit: templecuttingedge.files.wordpress.com; abdn.ac.uk; sagepub.com

Three common marine strategies:

2. Osmoconform and ion regulate• Sharks• Plasma concentrations > seawater • NaCl concentration ~1/3 seawater• Urea & Trimethylamine N-oxidase (TMAO)• Internal fluids ~5% saltier than seawater

• Rectal gland

Image credit: templecuttingedge.files.wordpress.com; abdn.ac.uk; sagepub.com

Three common marine strategies:

3. Osmoregulate• Teleosts • Regulate Na+ & Cl- ~1/3 seawater• Salt removal• Esophagus• Intestines• Gill chloride cells

Image credit: wikipedia.com; sagepub.com

Other regulators:

• Marine birds/reptiles

• Salt gland• Allows to drink saltwater and consume aquatic

(salty) plants and animals

Image credit: nicerweb.com; wordpress.com

Other regulators:

• Plants – mangroves

1. Roots prevent salt from entering but allow water in2. Excrete salt from glands on leaves3. Concentrate salt in old leaves, flowers, bark

Image credit: wikimedia.org

Three common marine strategies:

Units = mosmol

Solutes Seawater 1) Invertebrates & hagfish

2) Sharks 3) Teleosts

Na+ 470 500 350 180

Cl- 570 500 350 180

Urea 0 0 230 0

TMAO 0 0 170 0

Total 1040 1000 1100 360

Marine teleosts

• The problem• Internal fluids hypotonic to seawater• Constant water loss• Constant ion gain

Image credit: mrupp.info

Marine teleosts

• The problem• Internal fluids hypotonic to seawater• Constant water loss• Constant ion gain

• The answer• Drink constantly• Absorb NaCl and water from ingested seawater• Keep water• Excrete NaCl

Image credit: mrupp.info

How do they pull this off?

Image credit: mrupp.info

How do they pull this off?

American Physiological Society

• August Krogh Distinguished Lectureship

• Bodil Schmidt-Nielsen (1994)

• Jared Diamond (1995)

• Knut Schmidt-Nielsen (1996)

• George Somero (2000)

• Peter Hochachka (2001)

• David Evans (2008)

The characters:

• August Krogh• 1874-1949• Danish• 1920 Nobel Prize

for capillary blood flow

• Gas exchange• Respiration• Diffusion

• Homer Smith• 1896-1962• American• Kidney function

and structure• MDIBL

• Ancel Keys• 1904-2004• American• Krogh’s post-doc

in early 1930s• Influence of diet

on health

Image credit: nndb.com; niehs.nih.gov

The characters:

• August Krogh• 1874-1949• Danish• 1920 Nobel Prize

for capillary blood flow

• Gas exchange• Respiration• Diffusion

• Homer Smith• 1896-1962• American• Kidney function

and structure• MDIBL

• Ancel Keys• 1904-2004• American• Krogh’s post-doc

in early 1930s• Influence of diet

on health

Image credit: nndb.com; niehs.nih.gov

The characters:

• August Krogh• 1874-1949• Danish• 1920 Nobel Prize

for capillary blood flow

• Gas exchange• Respiration• Diffusion

• Homer Smith• 1896-1962• American• Kidney function

and structure• MDIBL

• Ancel Keys• 1904-2004• American• Krogh’s post-doc

in early 1930s• Influence of diet

on health

Image credit: nndb.com; niehs.nih.gov

Basis for question:

• Krogh, Smith, Keys, understood that marine fish were hyposmotic to seawater

• Consequences = dehydrate & gain salts

• How do they regulate against this?

Krogh with freshwater fish:

• Salt uptake from head region

• Probably gills

• Guessed at Cl-/HCO3- & Na+/NH4

+ exchangers

Smith with marine fish:• Continual drinking

• Intestines remove ions and water

• Extrarenal ion elimination pathway• Excess ions excreted through gills?

Image credit: Evans 2008

Keys with marine eels:

• Perfused heart-gill preparation

Image credit: Keys 1931

Keys with marine eels:

• Perfused heart-gill preparation

Image credit: Keys 1931

Keys with marine eels:

• Perfused heart-gill preparation

• Gills site of active Cl- excretion

These studies formed the framework for the model of ion regulation we use today

Image credit: Keys 1931

Chloride Cells - gill morphology

Image credit: imageshack.us; webshots.com

Image credit: Karnaky 1986; webshots.com

Chloride Cells - gill morphology

Chloride Cells

Image credit: Karnaky 1986; Degnan et al. 1977

Chloride Cells - Cl- current & opercular epitheliumChloride Cells - Cl- current & opercular epithelium

Ussing Chamber

Image credit: warneronline.com

Apical(seawater)

Basolateral(blood)

Opercular epithelium

Chloride Cells - Cl- current & opercular epitheliumChloride Cells - Cl- current & opercular epithelium

Ussing Chamber

Image credit: warneronline.com

Apical(seawater)

Basolateral(blood)

Current injection electrodeVoltage

recording electrode

Opercular epithelium

Chloride Cells - Cl- current & opercular epitheliumChloride Cells - Cl- current & opercular epithelium

Ussing Chamber

Image credit: warneronline.com

Apical(seawater)

Basolateral(blood)

Current injection electrodeVoltage

recording electrode

Cl-

Opercular epithelium

Chloride Cells - Cl- current & opercular epithelium

Image credit: Degnan et al. 1977

Chloride Cells - Cl- current & opercular epithelium

Image credit: Degnan et al. 1977

Chloride Cells - Cl- current & opercular epithelium

Image credit: Foskett and Scheffey 1982

Chloride Cells - the mechanism

Image credit: Evans 2008

Chloride Cells - the mechanism

Image credit: Evans 2008

-70 mV

-15 mV

Discussion Questions

• Trade-offs

• Energy required to kep up this process• Why no osmoconform and ion regulate as sharks do?• Euryhaline fish?

• Early, simplistic experimental approaches lost?

Chloride cells - Cystic Fibrosis (CF)• Caused by mutation in CFTR protein• In humans, creates

• sweat• digestive juices• mucous

• CF patients with CFTR failure• Cl- buildup thicker, nutrient-rich mucous in lungs

bacterial infection• Increased Na+ & Cl- uptake decreased water

reabsorption dehydrated thick mucous• Lungs, pancreas, intestine

• Most common fatal, inherited disease in U.S.• Life expectancy = 36 yrs

Three common marine strategies:

1. Osmoconform• Agnathan hagfish & many marine invertebrates• Conform internal [ion] to [external medium]• Blue crab example• Salinity < 28 ppt: regulate• Salinity > 28 ppt: conform

Image credit: flyingfishshop.com