Physiology: Biochemistry of the Pancreatic β-cell

Question 1

Name the transporter which allows glucose to enter the β-cell

Answer 1

GLUT2

Question 2

What is the function of the ATP-sensitive K+ channel KATP in insulin secretion?

Answer 2

The ATP-sensitive K+ channel is inhibited by increased ATP levels which are caused by increased glucose metabolism

This results in depolarisation of the cell membrane, allowing the opening of voltage-gated Ca2+ channels

Question 3

What is the function of the second phase of insulin secretion?

Answer 3

More tuned to the requirement, related to glucose intake (amount and duration)

Question 4

What is the function of the voltage-gated Ca2+ channels in insulin secretion?

Answer 4

Open in response to cell membrane depolarisation

An increase in internal Ca2+ concentration leads to fusion of secretory vesicles with the cell membrane and release of insulin

Question 5

β-cells only produce insulin in response to blood glucose arising above what level?

Answer 5

5 mmol/l

Question 6

Name the only cell in the body which produces insulin

Answer 6

β-cell

Question 7

What is the function of glucokinase?

Answer 7

Phosphorylates glucose and acts as a glucose sensor - a change of glucose concentration leads to a dramatic change in glucokinase activity

Question 8

Why is insulin release biphasic?

Answer 8

5% of insulin granules are immediately avaliable for release (RRP - readily releasable pool) Reserve pool must undergo preparatory reactions to be mobilised and avaliable for release - requires signalling processes related to the glucose exposure

Question 9

What is the function of the first phase of insulin secretion?

Answer 9

Prevents a sharp increase in blood glucose

Question 10

Describe the pattern of insulin release

Answer 10

Biphasic

Question 11

What percentage of insulin produced is secreted at a basal rate?

Answer 11

5%

Question 12

Describe the stages of the secretion of insulin

Answer 12

1. Glucose enters β-cells through GLUT2 and is phosphorylated by glucokinase
2. Increased glucose metabolism → increased intracellular ATP concentration
3. ATP inhibits ATP-sensitive K+ channel KATP
4. Depolarisation opens voltage-gated Ca2+ channels
5. Increase in internal Ca2+ concentration leads to fusion of secretory vesicles with the cell membrane and release of insulin