Lecture 9: Intercellular signalling

Question 1

What is intercellular signalling?

Answer 1

Signalling between cells

Question 2

Examples of intercellular signalling molecules

Answer 2

Hormones (proteins, peptides, steroids), neurotransmitters, and dissolved gases

Question 3

Why do cells need to communicate?

Answer 3

1. Communication with neighbouring cells
2. Adaption of metabolism and nutritional requirements
3. To induce/decease growth
4. Respond to danger signals
5. Trigger stem cell differentiation

Question 4

What are the 3 categories of membrane receptors?

Answer 4

1. Receptor linked to ion channels
2. G protein coupled receptors (GPCRs)
3. Receptors linked to enzymes

Question 5

How does intercellular communication typically work?

Answer 5

• Synthesis and release of the signalling molecule
• Transport of molecule to target cell for detection
• Change in cellular behaviour of cell triggered by activation of receptor
• Effect of receptor activation
• Removal of signal which terminates cellular response

Question 6

What triggers the cell to express different intercellular signalling receptors?

Answer 6

Gene expression causes cells to express different sets of receptors.

Question 7

Where are intercellular signalling receptors found?

Answer 7

Receptors can be located in the cytosol or in the nucleus; small molecules and hydrophobic molecules can cross the cell membrane.

Question 8

How can intercellular signalling molecules trigger multiple responses?

Answer 8

A signalling molecule may activate different receptor types or trigger different responses in different cells.
Eg. Adrenaline causes relaxation in smooth muscle cells in the gut and contraction in cardiac muscle cells because of the different receptors on these cells and their signalling pathways.
Eg. Acetylcholine can bind to M1 receptors, M2 receptors and Nicotinic-type receptors.

Question 9

What is endocrine signalling?

Answer 9

Long range signalling that utilises a compound produced by an endocrine gland (eg. hormone) which enters the blood stream

Question 10

What are hormones?

Answer 10

A compound produced by an endocrine gland and released into the bloodstream where it acts on a target cells at a distance location

Question 11

Example of endocrine signalling

Answer 11

Stress response- cortisol binds to nuclear receptor protein which causes a conformational change that allows it to pass into nucleus and bind to regulatory regions of target genes to activate transcription; activate and suppress gene expression producing both metabolic and anti-inflammatory effects.

Question 12

What is paracrine signalling?

Answer 12

Short range signalling between adjacent cells.

Question 13

Example of paracrine signalling

Answer 13

Nitric oxide (NO)- produced when blood vessel endothelial cells are stimulated by acetylcholine. NO diffuses into nearby smooth muscle cells and activates its target enzyme guanylate cyclase to activate it and make GMP from GTP. Cyclic GMP causes the smooth muscle cells to relax, and thus increases blood flow through the blood vessel

Question 14

How is angina treated? Example of paracrine signalling using NO

Answer 14

Nitroglycerin is converted in the body to NO, which is used to improve blood flow in the coronary arteries.

Question 15

What is neuronal signalling?

Answer 15

Signalling involving neurotransmitters which travel across synaptic gaps t adjacent cells (e.g. nerve cells and muscle cells).

Question 16

Example of neuronal signalling

Answer 16

Adrenaline is a neurotransmitter that regulates attentiveness and mental focus.

Question 17

What is autocrine signalling?

Answer 17

Signalling whereby cells secrete signalling molecules that bind their OWN receptors to generate a change in their OWN behaviour.

Question 18

Example of autocrine signalling

Answer 18

Epidermal growth factor (EGF); uncontrolled release of growth factors by cancer cells can lead to autocrine and paracrine signalling, stimulating cell proliferation which can lead to cancer.

Question 19

What is juxtacrine signalling?

Answer 19

Contact-dependent signalling between immediate neighbouring cells that does not require signalling molecules

Question 20

How does juxtacrine communication work?

Answer 20

Communication is via membrane bound molecules such as gap junctions and contact-dependent receptor ligand binding.

Question 21

What are gap junctions?

Answer 21

Channels called connexons which provide neighbouring cells with a direct communication link that can be opened or closed in response to the cell environment

Question 22

Example of juxtacrine signalling

Answer 22

Gap junctions appear in the myometrium of the uterus towards to the end of pregnancy, where they help coordinate uterine contractions during childbirth.