L3 - Cell Homeostasis - Na & Ca

Question 1

What is the function of the thick ascending limb of Henle’s Loop?

Answer 1

• Reabsorption of NaCl in prefernce to H20.
• It creates the transepithelial osmotic gradient
  resonsible for counter current multiplication.

Question 2

What is on the basolateral membrane of the ascending limb?

Answer 2

The Na/K pump that keeps the intracellular Na levels low.

Question 3

What is on the Apical membrane of the ascending limb?

Answer 3

K/Na/Cl- transporter (NKCC) that brings all 3 ions in.

Question 3

What is on the Apical membrane of the ascending limb?

Answer 3

K/Na/Cl- transporter (NKCC) that brings all 3 ions in.

Question 4

What happens if the Na+ is raised?

Answer 4

• NaCl reabsorption is inhibited, transepithileial osmotic gradient and this leads to DIURESIS and increased Na and Cl in the urine.
• It will take longer for an action potential to develop.
• Causes the ENa to be +30, a decrease in electrical gradient.

Question 5

What is the Na/K pump inhibited by?

Answer 5

Cardiac Glycosides - Ouabain and digoxin

Question 6

How does ouabain work?

Answer 6

binds to the extracellular pore of the protein causing conformational change and blocking.

Question 7

Why is regulation of Ca+ important?

Answer 7

because Ca is an important second messenger in many signalling pathways.

Question 8

How is intracellular Ca+ kept low?

Answer 8

By the Ca+ ATPase and the Na/Ca exchanger.

Question 9

What gene family is the Na/Ca exchanger part of?

Answer 9

• SLC8
• There are 3 forms NCX 1-3

Question 10

What is the function of the Na/Ca exchanger?

Answer 10

• It exchanges extracellular Na for intracellular Ca.
• Electrogenic

Question 11

The Ca+ ATPases

Answer 11

PMCA - plasma membrane calcium pumps -pump calcium across the
membrane outside of the cell.
SPCA - calcium pumps found on the Golgi apparatus.
SERCA - Ca+ pumps found on the sarcoplasmic membrane or
endoplasmic reticulum - pump calcium out of the cytoplasm
into the organelles which act as calcium stores.

Question 12

Role of PMCA

Answer 12

• The major mechanism for controlling Ca+ at resting levels
• Increases in Ca+ causes the activation of Calmodulin.
• Important when there are large influxes of Ca+.

Question 13

IP3 Receptors

Answer 13

Activated following the binding of IP3, expressed in most cell types.

Question 14

Ryanodine Receptors

Answer 14

• Low concentrations of ryanodine activate the channel and higher concentrations inhibit.
• Stimulated by caffeine.
• Natural activator is CDP ribose.