Session 7.3: Brief intro to cellular Ca2+ homeostasis

Question 1

how much calcium does the body contain and where is it mostly found

Answer 1

1kg, 99% in bones

Question 2

what are the blood serum calcium levels

Answer 2

8-10mg/dL or 1.9-2.3 mM (50% of which is free calcium)

Question 3

what regulated amount of calcium levels

Answer 3

intake
kidney function - excrete or reabsorb
bone calcium regulation

Question 4

what are the processes regulated by that control calcium levels

Answer 4

endocrine control:

1. calcium ion sensing receptors in parathyroid gland and parathyroid hormone produced
2. 1,25-dihydroxyvitamin D3
3. Calcitonin

Question 5

what is the concentration of calcium outside the cell in comparison to inside the cell and ER

Answer 5

1-2 x 10-3 M -> 1 x10-7 M

ER = 2-3 x10-4 M

Question 6

why is it important to maintain gradient of calcium gradient

Answer 6

changes in intracellular concentration = physiological processes

• muscle contraction
• neurotransmission
• fertilisation
• cell death
• regulation of metabolism
• learning and memory

Question 7

what do changes in calcium concentration look like

Answer 7

inside the cell, changes are usually 2-10 fold can alter how cell responds…changes within microdomains can be much greater
this causes oscillatory and peak plateau responses. the different pattern = different transcriptional programmes

Question 8

how are calcium concentration gradients set up and maintained

Answer 8

so intracellular less than extracellular

• impermeability of calcium through plasma membrane so not leak out (more in)
• pumps and transporters pump calcium out of cytoplasm (more out)
• ca buffer proteins (ca2+-binding proteins) (low levels inside)

Question 9

what are the different ATP dependent mechanism to maintain calcium concentration gradient

Answer 9

Ca2-ATPases: PMCA (out of cell), SERCA (into SR) - both against conc gradient
Transporter mechanisms: Na+, Ca2+ exchanger, sodium in down conc gradient (so dependent of Na/K ATPase), calcium out of cell against conc gradient

Question 10

what are the mechanisms to increase calcium concentration inside cell (cytoplasm)

Answer 10

from outside the cell: ligand gated ion channels (bind agonist, gates, allows ca down conc gradient)
voltage gated calcium channels (senses membrane potential, depolarises, allows ca in)
from outside the SR/ER: IP3 receptors, Ca induced ca released receptors (ryanodine receptors)