Brief Introduction to Cellular Ca2+ Homeostasis

Question 1

What is Ca2+ homeostasis regulated by?

Answer 1

Intestinal Ca2+ uptake
Ca2+ reabsorption in the kidneys
Bone calcium regulation

Question 2

What are these processes under control by?

Answer 2

Endocrine control
Ca2+ sensing receptor in the parathyroid gland
PTH
Calcitonin

Question 3

Where can you find calcium ions?

Answer 3

Blood

Cytoplasm and ER/SR

Question 4

Is the extracellular or the calcium in the cytoplasm’s concentration greater? By how much?

Answer 4

Blood’s calcium concentration is 10000 times greater.

Question 5

Is the cytoplasmic calcium or the SR/ER calcium’s concentration greater?

Answer 5

SR/ER is greater. By around 1000x times.

Question 6

Give a scale of greater to lesser concentration of calcium.

Answer 6

Blood>SR/ER>Cytoplasm

Question 7

What processes is this difference in calcium ion concentration important for?

Answer 7

Muscle contraction
Neurotransmission/stimulus-secretion coupling
Fertilisation
Cell death (apoptosis, necrosis)
Regulation of metabolism
Learning and memory

Question 8

How are Ca2+ concentration gradients set up and maintained?

Answer 8

There’s a relative impermeability of the plasma membrane to Ca2+.
Pumps and transporters move Ca2+ out of the cytoplasm.
Ca2+ buffer proteins.

Question 9

Give 3 examples of pumps and transportes that move Ca2+ out of the cytoplasm.

Answer 9

Ca2+ ATPase called PMCA
SR/ER Ca2+ ATPase called SERCA
Na+/Ca2+-exchanger called NCX

Question 10

How does the NCX work?

Answer 10

Na+ goes in

Ca2+ goes out

Question 11

Give four examples of mechanisms that increase the Ca2+ concentration in the cytoplasm.

Answer 11

On plasma membrane:
Voltage-operated Ca2+ channels (VOCC)
Ligand-gated ion channels (LGIC)
On ER/SR membrane:
Ca2+ induced Ca2+ release (CICR also called ryanoidine receptors)
IP3 receptors