S3) Intracellular Calcium Regulation

Question 1

Ca²⁺ concentration varies greatly inside and outside the cell.

What is the value for extracellular [Ca²⁺]?

Answer 1

Extracellular [Ca²⁺] = 1 x10^-3 M

Question 2

Ca²⁺ concentration varies greatly inside and outside the cell.

What is the value for intracellular [Ca²⁺]?

Answer 2

Cytoplasmic [Ca²⁺] = 1 x10^-7 M

Question 3

Ca²⁺ concentration varies greatly inside and outside the cell.

What is the value for ER/SR [Ca²⁺]?

Answer 3

ER/Sarcoplasmic reticulum [Ca²⁺] = 2 x10^-4 M

Question 4

Identify 2 processes which mediate increases in cytoplasmic Ca²⁺ concentration

Answer 4

• Movement of Ca²⁺ across the plasma membrane
• Release of Ca²⁺ from the ER/SR

Question 5

Identify 3 factors which oppose increases in cytoplasmic Ca²⁺ concentration

Answer 5

• Relative impermeability of the plasma membrane to Ca²⁺
• Pumps and transporters that move Ca²⁺ out of the cytoplasm
• Ca²⁺-binding proteins

Question 6

Identify the 3 mechanisms that maintain low [Ca²⁺]_i and reverse increases in [Ca²⁺]_i

Answer 6

• PMCA – pumps calcium out across plasma membrane (ATP)
• SERCA – pumps calcium into SR/ER (ATP)
• NCX (Na⁺, Ca²⁺ exchanger) - sodium enters cell and calcium exits

Question 7

Identify the 4 mechanisms which increase intracellular [Ca²⁺]

Answer 7

- Calcium movement across plasma membrane:

I. Voltage operated Ca²⁺ channels (VOCC)

II. Ligand-gated ion channels (LGIC)

• Calcium movement out of the ER/SR:

I. Ryanodine receptors (Ca²⁺-induced Ca²⁺ release)

II. IP₃ receptors

Question 8

In terms of signalling pathways in action, outline the inotropy of the heart

Answer 8

Both blood-borne adrenaline and sympathetically released noradrenaline can interact with ventricular β_2-adrenoceptors to increase the force of contraction (+ve inotropy)

Question 9

In terms of the Gq signalling pathway in action, outline smooth muscle contraction

Answer 9

• Sympathetically released noradrenaline interacts with vascular smooth muscle α₁-adrenoceptors to cause vasoconstriction

- Parasympathetically released acetylcholine interacts with bronchiolar smooth muscle M₃-muscarinic receptors to cause bronchoconstriction