Hypo-osmotic - Hypo-ionic Regulation

Medium osmolarity (mOsm)

0 1000

1000E

CF

osm

olar

ity (

mO

sm)

e.g. Uca, Artemia

marine teleosts

Crustacea:

• Uca - hemolymph Na = 447 mM in175% sw (~ 800 mM)

• Artemia - hemolymph Na = 300 mMin as much as 4-5 M NaCl !!!

500 mM NaCl1000 mOsm

200 mM NaCl400 mOsm

H2O ion(s)

Problems:• osmotic water loss• diffusive salt gain

H2Oions

Solutions:• drink sea water

• ion uptake by gut• active salt extrusion

Marine Teleost

ant. post.mM

Fluid absorption across teleost gut:NO ACTIVE TRANSPORT OF H2O!

Must move ions and cause H2O to move by osmosis

s.w.Na = 450K = 9Cl = 520

Blood:

Na = 200K = 4Cl = 190

Na = 100K = 6Cl = 90

Na = 20K = 0.8Cl = 50

ions H2O

>95% of salts absorbed

~75% of H2Oabsorbed

lumen of gut

blood (serosa)

Cl-

HCO3-

ATP ADP+ Pi

Cl-

H+

Na+ATP

ADP+ Pi

Na+

K+

Na+Cl-

CC - mitochondria-rich chloride cellAC - accessory cell, PC - pavement cell

From Evans et al. (1999) J. Exp. Zool. 283: 641-652.

Apical pit of chloride cell on surfaceof gill lamella

From Evans et al. (1999) J. Exp. Zool. 283: 641-652.

Gill epithelial cell Blood

Isosmotic - Hypo-ionic Regulation

mMNa Cl TMAO + urea mOsm

Sea Water 450 500 0 1000

Hagfish Plasma 549 550 0 1150

Teleost Plasma 160 200 0 400

Elasmo. Plasma 290 300 350-400 1000

S.W.500 mM NaCl1000 mOsm

300 mM NaCl1000 mOsm

ion(s)Problem:Diffusive salt gain

Solution:Active salt excretion

Elasmobranchs retain nitrogenouscompounds as osmotic effectors:

H2N C = O

H2Nurea

CH3

H3C N = O

CH3

trimethylamine oxide(TMAO)

mMNa Cl TMAO + urea mOsm

Sea Water 450 500 0 1000

Plasma 250 250 420 1000

Urine 250 250 110 800

Rectal gland fluid 500 500 20 1000

Urea and TMAO are reabsorbed from theurine.

Salt is excreted via rectal gland and chloridecells in the gills.

Hyperosmotic-Hyperionic Regulation

Medium osmolarity (mOsm)

0 1000

1000E

CF

osm

olar

ity (

mO

sm)

e.g. freshwater fish &crustaceans

e.g. estuarinecrustaceans

150 mM NaCl300 mOsm

2 mM NaCl5 mOsm

H2O ion(s)

Problems:• osmotic water gain• diffusive salt loss

Freshwater crayfish, Astacus

H2Oions

antennalgland

Solutions:• produce copious urine

• urinary salt loss • decrease permeability• active ion uptake

NaCl

Na+ Cl-

Freshwater Fish (Teleost)

Voluminous, dilute urine

Don’t drink the water

Water Gill Epithelium