Lecture 5.5 Calcium Homeostasis

Question 1

what regulates whole body calcium homeostasis

Answer 1

interstitial Ca2+ uptake
Calcium readsorption in the kidneys
Bone calcium regulation

Question 2

what controls the calcium processes

Answer 2

Ca sensing receptors in the parathyroid gland
parathyroid hormone
1,25 - dihydroxyvitamin D3
calcitonin

Question 3

how is calcium concentration distributed in and around the cell?
Why is this important? (only need a couple examples)

Answer 3

high extracellulary - 1.3 mMoles
Very low intracellulary - 100 nMoles
quite high in the endoplasmic recticulum - 0.2mMoles

changing the ca conc intracellulary via these ion gradients is used in many physiological and pathalogical cell processes such as:

muscle contraction
neurotansmission
fertilzation
apoptosis
regulation of metabolism
learning and metabolism

Question 4

how do we set up and maintain ca2+ gradients?

Answer 4

the plasma membrane is fairly impermeable to calcium
pumps and transporters move ca out of the cytoplasm
ca buffer proteins bind to calcium

ATP dependent ca2+ ATPases (PMCA,SERCA) will remove calcium to the extracellular matrix and Endopalsmic recticulm respectively.

transporter mechansims such as NCX - na2+ in ca2+ out

all of this keeps ca2+ conc very low in the cytoplasm

Question 5

what are the mechanisms to increase Ca2+ in the cell

Answer 5

influx of ca across the plasma membrane via voltage operated Ca 2+ channels (VOCC)
and ligand gated ion channels

Calcium induced calcium release from the ER via CICR (ryanodine) receptors and IP3 receptors

Question 6

what does a calcium change look like ?

Answer 6

are usually 2 - 10 times the base level in seconds
small areas can change by greater than this in milliseconds
possible to have complex patterns of ca infulx/outflux (oscillation), and non uniform changes to act as specific cell signals