Lecture 31: Osmoregulation 1

What are the Four features of transport epithelia?

1) Asymmetrical distribution of membrane transporters -Solutes selectively transported across membrane 2) Cells interconnected to form impermeable sheet of tissue -Little leakage between cells 3)High cell diversity within tissue 4) Abundant mitochondria -Large energy (ATP) supply Epithelial cells: Important barrier in humans and in fish gills in maintaining osmolarity: Has Polarity ~ Apical side (facing outside/water) ~ Basolateral side (facing the inner environement) _ has ion channels located on different asymmetrically - Tight junctions (so water doesn't leak out, mitochondria (pumps ions against concentration gradient)

What are the two levels that osmo regulation occurs?

1) Intracellular fluid 2) Inside the cells Concept: depends on the animal ~ Bulk flow into water ~ Gas exchange ~ Sea water has salt. Body and water have different osmolarity levels. We have a way to protect our inner environment. The cells are surrounded by blood (extracellular fluid). We have skin (protection) as an epiderm as a barrier.

Epithelial cells use two main routes of transport

1) Transcellular transport -Movement through the cell across membranes 2) Paracellular transport -Movement between cells -"Leaky" vs. "tight" epithelia -Types of transporters •Na+/K+ATPase •Ion channels (Cl-, K+, Na+) •Electroneutral cotransporters •Electroneutral exchangers

Can divide animals into four groups based on terminology. What are the four categories?

1. Osmoconformer: external and internal osmolarity correlate 2. Osmoregulator: ion concentration of blood is regulated. 3. Stenohaline: narrow range of salinity 4. Euryhaline: wide range of osmolarity range 1- Euryhaline osmofonformer allows osmolarity to decrease in parallel with water until death 2- Stenohaline osmoconformer dies after very modest osmotic disruption 3- Euryhaline osmoregulator defends a nearly constatnt internal state but eventually succumbs 4- Stenohaline osmoregulator can defend its internal osmolarity over a narrow range of external osmolarities

Propertiea of mammalian fluids and aquatic environments

Human blood: ~ Salty ~ Osmolarity = 300 mOsM (too high or low detrimental to life) ~Na and Cl are the main contributors ~Other contributors: K, Ca, Mg (a little bit less of a contribution) The table is a little bit complicated. ~ Seawater: high osmolarity, high Mg ~Freshwater: osmolarity <5 ~ Salt Lakes: 50-3000 mOsM

Bony fish (gold fish, zebrafish, cod) are osmoregulators

Hyperosmotic environment - Problem: loss of H20, Ions diffuse in - Soluton: drink LOTS of H20 (small amount of urine), gills remove the NaCl ~Sourrounding environment is hyper osmotic -Inside body= 300 -Outside environment = 1200 Hypo osmotic environment - Problem: Gains H20, Loses NaCl - Soluton: don't dirnk water (large amount of urine), gills uptake LOTS of NaCl ~Surrounding water is hypo osmotic to their body - inside body = 300 - Outside environment = 5

Strategies to meet ionic challenges

Ionoconformer -Exert little control over ion profile within the extracellular space -Exclusively found in marine animals ~ don't fight ion concentration of blood. »For example, many invertebrates Ionoregulator -Control ion profile of extracellular space ~ion concentration of blood is regulated. »For example, most vertebrates

Ionic and Osmotic Challenges

Marine environments •Animals tend to gain salts and lose water ~Surrounding is high in salt, Seawater is Hyperosmotic to animal (tend to loose water) Freshwater environments •Animals tend to lose salts and gain water ~ Water osmolarity is low, hypo-osmotic environment = they tend to loose salt Terrestrial environments •Animals tend to lose water ~can't loose to much water or we will die (humans are terrestrial) Many animals move between environments and must be able to alter their homeostatic mechanisms

a)A perturbing solute is show to increase Km whereas a compatible solute has no effect. b) Urea is shown to increase Km and TMAO decreases Km, but the combination of the two has no effect.

Marine invertebrates and ancient fish (such as lamprey and cartilaginous fish) are omsmoconformers Osmolarity in the body is controlled by solutes in the body. Lamprey and shark are osmoconformer (body salt concentration can be very high) they can use different types of solutes. Types: 1.Proturbing solutes (ex. NaCl) The higher can decrease binding affinity of the enxzyme. Stops enzyme from working. 2.Compatible solute (amino acid) can contribute to the total osmolarity because they are organic chemicals, don't damage enzymatic activity. Can still bind substrate with similar affinity. Can increase osmolarity and enxymatic activity can still work. 3.Counteracting solutes: ~Urea- proturbing solute( the higher the less efficient the enzyme ~TMAO- the higher the better the enzyme can work ~~~~Together (Urea + TMAO) = cause neutralization. This means very high salinity and enzymes can still work.

Osmoconformer vs osmoregulator vs ionoconformer vs ionoregulator table

Most of the osmoconformers live in marine environment (high osmolarity/ 1000 mOsM). None can live in freshwater because if osmolarity 5 the animal will die. This figure shows proportions of NaCl. Bony fish (salmon): very different of 300 mOsM = osmoregulator. NaCl levels way lower than enviorment since NaCl is very low so they are also Ionoregulators. Hagfish: ectracelllular fluid. almost identical NaCl to environment (ionoconformer) and mOsM almost identical to environment and so Osmoconformer. Elasmobranch and Marine bivalve: Osmoconformer and Ionoregulator.

isosmotic vs hyperosmotic vs hyposmotic

Muscle cell into solution. Our cells are surrounded by phospholipids in buffer solution. We can measure the Osmos concentration (salinity). Both are bad for cell: (osmolality(salt) is different from molar concentration) More salt added= water goes out of cell More water added= osmolarity is decreased. Water diffuses into the cell, the cell expands. ~ concept: always refers to something else

Strategies to meet osmotic challenges?

Osmoconformer -Internal and external osmolarity similar »For example, marine invertebrates Omoregulator -Osmolarity constant regardless of external environment »For example, most vertebrates

Saltwater-Freshwater Transitions

Some fish migrate between saltwater and freshwater (diadromous fish) Catadromous -Eels: Live in freshwater, migrate to saltwater to spawn - Salmon: Live in saltwater; migrate to freshwater to spawn Ion transport functions of epithelia must change during migration •Controlled by hormones

Ability to cope with external salinities

Stenohaline -Can tolerate only narrow range Euryhaline -Can tolerate wide range

mOsmo =

measures osmolality, it's a unit.

Fish gill lamellae composed of

•Mitochondria-rich chloride cells •Pavement cells -Some mitochondria-rich -Some mitochondria-poor •Transport likely carried out by mitochondria-rich cells Marine fish have two cell types 1.Chloride cells (mitochondria rich) 2.Pavement cells (supporting cells, provides support for cell to work) ● ● Epithelial cells are asymmetrically placed. ~ NaCl must be transported out to maintain osmolarity ~ They import chloride from the Freshwater fish have three cell types: 1.Pavement cell (supporting cell) 2.PNA+ (positive) cell: Mitochondria rich Chloride cell -> get stained by PNA stain 3.PNA - (negate) cell: Mitochondria rich -> important for ion transport ● PNA - cell: important for Na uptake (low pH in this area) PNA + cell: important for Cl & Ca uptake ~ As a result body uptakes NaCl ● CO2+ H20-> Bicarbonate CA+ carbonate anhydrase Bicarbonate co-exchanger