Sodium Linked Transporters

Question 1

What is a sodium linked transporter?

Answer 1

Transporters which couple the free energy of a Na+ gradient to transport of a substance uphill

Question 2

In Na⁺/K⁺ ATPase, one ATP moves how many Na+ and in which direction?

Answer 2

3Na+ from cytosol to outside

Question 3

In Na+/K+ ATPase, one ATP moves how many K+ and in which direction?

Answer 3

2K+ into the cell

Question 4

Is the concentration of K+ high or low inside cells?

Answer 4

Usually high

Question 5

Is the concentration of Na+ high or low outside cells?

Answer 5

High

Question 6

What is the general structure of solute sodium symporters?

Answer 6

• 14 transmembrane helices with an inverted repeat topology
• TM2-6 and TM7-11 are upside down relative to each other

Question 7

How do transporters work together to get glucose from the gut into the blood?

Answer 7

• Glucose-Na+ symporter moves glucose into epithelial cells
• Na+/K+ ATPase transports the Na+ out of the cell
• Glucose then flows down a concentration gradient through GLUT into blood

Question 8

Where is the sugar binding site in sodium-galactose symporters?

Answer 8

At the centre of the inverted repeat

Question 9

What must happen for the sodium-galactose transporter to flip into an inward conformation?

Answer 9

Both sodium and galactose must occupy the binding site

Question 10

How many Na+ from the sodium gradient are required to drive 1 calcium out of the cell in the Na+/Ca+ antiporter?

Answer 10

3 sodiums

Question 11

Why is the Na+/Ca2+ antiporter useful in cardiac myocytes?

Answer 11

• Antiporter mops up any Ca²⁺ from the sarcoplasmic reticulum once muscle contraction has finished

Question 12

What does digoxin inhibit?

Answer 12

Na+/K+ ATPase

Question 13

Why is digoxin useful for the treatment of irregular heartbeat?

Answer 13

• Reduces the Na+ gradient
• This drives the efflux of calcium giving a higher resting calcium gradient
• This allows the muscle cell to become more contractible