Calcium signalling

Question 1

Calcium (Ca2+)

Answer 1

• is a universal and ubiquitous intracellular messenger
• has the highest gradient across the membrane (at resting potential, there is more extracellular calcium)

Question 2

Why is there less intracellular calcium levels at resting potential?

Answer 2

High concentrations of calcium are toxic to the cytosol

Question 3

Calcium stores in the cell

Answer 3

Is stored in the lumen cells and nuclear envelope and released when needed through receptors of voltage-gated Ca2+ channels

Question 4

What does the cell do regarding high calcium levels?

Answer 4

It removes calcium to maintain a regular low cytosolic Ca2+ concentration

Question 5

Method 1 - removing calcium out of the cell

Answer 5

Uses pumps to remove Ca out of the cell

Question 6

Plasma membrane PMCA pumps (calcium/ATPase)

Answer 6

In: 2H
Out: 1Ca
Energy used: 1ATP

Question 7

Exchanger: Ca K/Na pump

Answer 7

In: 4Na
Out: 1Ca and 1K

Question 8

Exchanger: Ca/Na pump

Answer 8

In: 3Na
Out: 1Ca

Question 9

Method 2 - Sequestering Calcium into intracellular stores

Answer 9

Calcium is stores in endoplasmic reticulum (ER) or sarcoplasmic reticulum (SR) and other organelles such as nuclear envelope, endosomes, lysosomes and mitochondira

Question 10

Why does the cell need to have adequate calcium stores?

Answer 10

Inadequate storage can lead to cell remodelling transformations into malignant cells

Question 11

What is the main storage of calcium?

Answer 11

Endoplasmic reticulum

Question 12

What is the SERCA pump?

Answer 12

SarcoEndo reticulum calcium ATPase pump

Question 13

MCU

Answer 13

Mitochondria calcium uniporter which is active when Ca hits 1yl. Pumps Ca from cytosol into mitochondrial matrix for temporary removal

Question 14

Method 3 - chelating calcium using calcium binding proteins

Answer 14

buffers (e.g calbindin and calquestrin) in the cytosol bind to calcium to prevent Ca ion mobility

Question 15

Calcium sensors e.g protein kinase C

Answer 15

catch calcium and bind directly until the cell resolves its gradient

Question 16

Units of calcium signalling mechanism

Answer 16

Stimulus > generation of calcium mobilising signals > ON mechanism

Question 17

How do our cells use Calcium in signalling?

Answer 17

Skeletal muscle, neurones, pancreatic acinar cells

Question 18

Use in skeletal muscles

Answer 18

calcium is released from the SR and interacts with sensors to trigger contraction and synthesise glucose and ATP for energy
= contraction

Question 19

Use in neurones

Answer 19

produces localised pulse of calcium signal to trigger exocytosis = mobilises Ca from ER

Question 20

Use in pancreatic acinar cells

Answer 20

in the pancreas, calcium activates secretion

Question 21

What is the difference in Ca use between skeletal muscle and neurons, and in the pancreas?

Answer 21

The pancreas in non-excitable and don’t have voltage gated calcium ion channels = they require a stimuli to produce secondary messengers and release Ca stores

Question 22

Ca2+ entry in excitable cells

Answer 22

1. Calcium enters through voltage gated channels
2. Second messengers of electrical signalling initiate different cellular events

Question 23

Ca2+ entry in non-excitable cells

Answer 23

1. Calcium enters through Ca2+ stores which are activated in response to low Ca2+ levels

Question 24

Why are physiological Ca2+ spikes localised in the pancreatic acinar cells?

Answer 24

The spikes occur in the secretory granule, which is surrounded by mitochondria - take up Ca2+ during calcium release. Mitochondria also release ATP where it’s needed after Ca release