Active Transport - The Sodium Pump

Question 1

What is the effect of [K+]o on digoxin inhibition of the sodium pump?

Answer 1

Increasing Potassium concentration on the outside decreases the affinity between cardiac glycosides and the sodium pump, therefore decreasing inhibition

Question 2

What is the therapeutic index?

Answer 2

Dose producing toxicity in 50% of the population

OR

Minimum effective dose for 50% of the population

Question 3

What is hypokalaemia?

Answer 3

Low levels of potassium in blood

Question 4

What is hyperkalaemia?

Answer 4

High levels of potassium in blood

Question 5

What are diuretics?

Answer 5

Drugs e.g.: Flurosemide

• Diuretics increase urine output by the kidney
• Treatment for high BP and excessive fluid retention
• Side effects: increased urinary excretion of potassium

Question 6

How does cardiac glycoside toxicity arise?

Answer 6

• Patient has congestive heart failure, therefore they are prescribed digoxin
• They might develop acute pulmonary oedema (excess fluid on lungs), and to get rid of that fluid, they prescribe diuretics (e.g. Furosemide)
• Diuretics increase urine output but also increase urinary excretion of Potassium
• Patient becomes hypokalaemic, increasing digoxin binding to Sodium pumps, inhibiting that
• Because of the very narrow therapeutic index, the patient develops digoxin toxicity

Question 7

How is cardiac glycoside toxicity solved?

Answer 7

Administering digoxin binding antibody

- Digibind binds to digoxin, causing it to dissociate from the Sodium pump

Question 8

Difference between the primary and secondary active transport?

Answer 8

Primary
- active transport systems directly couple the hydrolysis of ATP to molecular movement

Secondary

• active transport system use the energy stored in the Na+ gradient generated by the Sodium pump
• can be in one direction or opposite directions

Question 9

What is facilitated transport?

Answer 9

Move solutions in either direction of the cell

e.g.: glucose transporters (GLUT1, GLUT2, GLUT3…etc)

Question 10

Where is glucose concentration higher - in or out of cell?

Answer 10

Out of cell

Question 11

Give an example for secondary active co-transporting?

Answer 11

Na+ dependent glucose transport

- they cross the membrane together (different from GLUT transporters)

Question 12

What are the Na+ dependent glucose transporter isoforms?

Answer 12

SGLT1
- 2Na+ : 1 glucose

SGLT2
- 1Na+ : 1 glucose

They reabsorb glucose into the cell in intestines and kidney tubules for example