Osmolarity, Tonicity and Cell Preservation

Question 1

What is the most plentiful cation in the plasma?

Answer 1

Sodium ions.

Question 2

What is the most plentiful cation in cells?

Answer 2

Potassium ions.

Question 3

Are chloride ions found in higher concentrations inside or outside the cell?

Answer 3

Much higher outside the cell in the plasma.

Question 4

How is the positive charge of potassium ions inside cells neutralised?

Answer 4

By a variety of anions such as proteins, nucleic acids and phosphorylated proteins.

Question 5

What is the main intracellular anion?

Answer 5

Organic phosphate is the main intracellular anion and is a key intracellular metabolite with roles in ATP production and cell signaling.

Question 6

Are proteins cations or anions?

Answer 6

Anions.

Question 7

Proteins are found in relatively low concentrations but still have a measurable effect on the cell’s polarity. How is this possible?

Answer 7

They can have a highly negative charge (e.g. -17).

Question 8

How does the pH of the plasma differ from the pH of cells?

Answer 8

Plasma is more neutral and more basic than cells at 7.4 compared to 7.1 of cells.

Question 9

How does the osmolarity of plasma differ from cells? What is the significance of this?

Answer 9

It doesn’t, meaning there is not normally a significant osmotic effect (except for some regions of the kidneys where fluids are concentrated/diluted).

Question 10

Osmosis moves water to an area with a higher or lower osmolarity?

Answer 10

Higher (think water moves towards salt, NaCl, which has an osmolarity of 2 mOsmoles, assuming 1mmol/L)

Question 11

What is an osmole?

Answer 11

An osmole is the number of moles of solute that contribute to the osmotic pressure of a solution.

Question 12

How do you calculate the number of mOsmoles?

Answer 12

1mmol/L of MgCl2 would be 3mOsmoles because 3 ions make up MgCl2.
2mmol/L of NaCl would be 4 mOsmoles because 2(2 ions) = 4.
Glucose has a mOsmole of 1 assuming a concentration of 1mmol/L

Question 13

What is tonicity?

Answer 13

Tonicity is the strength of a solution as it affects the final cell volume.

Question 14

What does tonicity depend on?

Answer 14

Tonicity depends on both cell membrane permeability and the solution composition.

Question 15

Describe a hypertonic solution and its effect on a cell.

Answer 15

In hypertonic solutions, the osmolarity of the impermeant solutes outside the cell is greater than those inside the cell. The cell therefore shrinks (water moves out to reduce [solutes outside] and water moves towards areas of higher osmolarity).

Question 16

Describe a hypotonic solution and its effect on a cell.

Answer 16

In hypotonic solutions, the osmolarity of the impermeant solutes outside the cell is the are less than those inside the cell. The cell, therefore, swells in the solution.

Question 17

What is a negative consequence of differences in osmolarity between a cell and its enviroment?

Answer 17

Differences in the concentrations of permeant solutes can result in transient damages to cell volume. If the difference is very large, it can result in cell damage.

Question 18

How are cell volumes maintained?

Answer 18

Ion pumps keep the osmolarity of the cell equal to its surroundings.

Question 19

How are sodium and potassium concentrations maintained?

Answer 19

The Na+K+ ATPase pumps prevent the higher extracellular concentration of Na+ from entering the cell (and causing it to burst)) and vice versa with potassium.

Question 20

How do we preserve tissues that have been cut off from oxygen?

Answer 20

Put in cold temperatures (about 4 degrees) to slow the ischaemic changes.
Perfuse the cell with UW (University of Wisconsin) solution to reduce hypothermic cell swelling and enhance preservation.

Question 21

Why can putting a cell in cold temperatures cause further problems?

Answer 21

The Na+K+ ATPase pump stops functioning below 15 degrees, which is compounded by the lack of oxygen.

Question 22

What are the three main factors that serve to reduce cell swelling in UW-infused tissues?

Answer 22

Lack of Na+ or Cl- (so no influx/efflux possible).
Presence of extracellular impermeant solutes.
Presence of a macromolecular colloid.

Question 23

How can allopurinol and glutathione help preserve cells?

Answer 23

They act as antioxidants, preventing damage from ROS.