CELL HOMEOSTASIS

Question 1

Under normal conditions what is the approximate [EC] sodium ions?

Answer 1

145mM

Question 2

Under normal conditions what is the approximate [IC] sodium ions?

Answer 2

15mM

Question 3

Why is it important to keep a large gradient of sodium ions between the EC and IC compartment?

Answer 3

A large electrochecmical gradient allows fast action potential to develop and higher conductivity.

Question 4

What is a key transporter that keeps sodium homeostasis?

Answer 4

Sodium/Potassium ATPase

Question 5

How does the Na/K ATPase work?

Answer 5

Extrudes 3 sodium ions and takes in 2 potassium ions coupled by the hydrolysis of ATP.
2

Question 6

How can the rate of transport of the ATPase be affected ?

Answer 6

[Na]
[K]
[ATP]

Question 7

What can inhibit the the Na/K ATPase?

Answer 7

Cardiac glycosides such as ouabain and digoxin.

Question 8

What is the order of hierarchy in terms of concentrations?

Answer 8

Mole
Millimole
Micromole
Nanomole

Question 9

Under normal conditions, what is the [EC] Calcium ions?

Answer 9

1mM (1000000nM)

Question 10

Under normal conditions, what is the [IC] Calcium ions?

Answer 10

0.0001mM (100nM)

Question 11

What is the concentration difference between the outside and the inside of the cell in terms of calcium ions?

Answer 11

10,000 fold difference

Question 12

What are the two mechansims of calcium control?

Answer 12

Na/Ca exchanger

Ca ATPase

Question 13

How does the Na/Ca function?

Answer 13

The exchanger exchanges extracellular Na ions for Ca ions in a ration of 3 to 1 respectively.

Question 14

How is is possible to keep the intracellular concentration of calcium ions so low when there is only a 10 fold concentration difference in sodium ions?

Answer 14

By transporting 3 sodium ions at a time, the sodium gradient is effectively cubed.

Question 15

What family does the Na/Ca exchanger fall into?

Answer 15

SLC8 gene family, a part of the CaCA family. In mammals, 3 forms exist: NCX1-3

Question 16

What are the Ca ATPases?

Answer 16

Cells contain three types of Ca ATPases:
PMCA - plasma membrane
SERCA - endoplasmic reticulum
SPCA - golgi apparatus

Question 17

Calcium is an important second messenger. What are the plasma membrane pathways used in calcium signalling for influx into the cytoplasm?

Answer 17

1. Voltage operated calcium channels (VOCC)
2. Receptor operated calcium channels (ROCC)
3. Mechanically activated calcium channels (MACC)
4. Store operated calcium channels (SOCC)

Question 18

What are examples of SOCC?

Answer 18

1. IP3 receptors - channels activated by IP3 binding

2. Ryanodine receptors - low concentrations of ryanodine activate the channels and higher concentrations inhibit.

Question 19

Caffeine and cADP ribose are examples of activators of what receptors?

Answer 19

Ryanodine

Question 20

What is STIM1

Answer 20

A calcium binding protein that forms a physical link between depleted calcium stores and plasma membrane calcium channels to physically open the channel and refill the stores.