Physiology 3140A Lecture Notes - Lecture 15: Vascular Endothelial Growth Factor, Paracrine Signalling, Synaptic Plasticity
2 May 2018
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Cell Physiology 3140 Lecture 15
Receptor and Cell Signalling
October 20 2017
Multicellular organisms: made up of cells
- Cells communicate by sending and receiving signals
- Signals originate from:
o Environment
o Other cells
o Enable us to stay alive
- Communicate by sending out signals from hormones, neurotransmitter, chemicals released, etc.
- OR cells get communicated with some physical things (that receptors pick up on) including:
o Photons of light
o Heat + lack of heat
o Vibration
o Sound
o These can be considered a type of ligand; receptors get this information and use the
information to communicate into the cell cell can respond by releasing a chemical, being
another signal that transmits to other cells
Forms of intercellular signaling
CONTACT DEPENDENT SIGNALLING:
- Signaling molecules remain bound to surface of signaling cell
- Activate target cells that come into contact with signaling cell
- Important in developmental biology
- Critical for development of tissues, synaptic plasticity
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- In brain, the synapses are changing constantly – synapses are always modifying themselves; adding
or losing synapses, alter strength of existing synapses - in response to something you are doing
o Take place by modifying interactions between cells
o Molecules present on the target cell and the signaling/input cell being able to receive that
▪ E.g. Ephrin, integrin
- Target cell will express a cell surface signal a signaling cell will have a ligand to interact with it
- How a lot of tissues are formed or cells migrate to find out what they are supposed to be by finding
these receptors
o Not releasing chemicals, but have feelers on their cell surface
o Moving along and looking for their receptor -> know that is they are supposed to land, make
contact + develop
ENDOCRINE SIGNALLING
- Endocrine cells release hormones into the bloodstream - transported throughout body (signaling
over long distances)
- Hormones act on target cells that express a receptor for the ligand
- Hormone signaling is a relatively slow (minutes-hours-days)
- Long distance signaling release hormone get into blood system and travel around the body
- Find target cell based on the receptors that are expressed on the surface of the target cells
o Target cell can be on the other end of the body
- Target cell that will respond to it, will ONLY be those that express that specific receptor; no receptor
= not effected by the hormone
o There could be other cells present, but will not be effected by the hormone because they lack
the receptor
- Transported throughout the body, signaling over long distance, hormone acts only on target cell with
specific receptor
- LONG TERM EVENTS
o Over minutes to hours to days
o Due to the nuclear event engagement; changes in gene expression, protein expression this
can take a long time
- Engage many tissues and organs in the body
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find more resources at oneclass.com
PARACRINE SIGNALLING (Para = near)
- Secreted signaling molecules act as local mediators that impact
target cells only in the immediate environment
- Example of ligands:
o Platelet-derived growth factor (PDGF)
▪ Wound healing
o Fibroblast growth factor (FGF)
▪ Cell growth, differentiation
- NEAR SIGNALLING
- Signaling cell that is releasing something (hormone or substance; a local mediator)
o Local mediator interacts with cells in the IMMEDIATE environment
o Looking at within a tissue rather than multi-organ
- Endocrine signal engages a number of different organs in the body BUT paracrine signaling engages a
tissue or a local environment within the tissue because they are LOCAL mediators
- Why would the signal only want to be local?
o What characteristic about the ligand would indicate that it has to be a local event?
o Local mediator has a short half life – degrades spontaneously, can be broken down by
enzyme, or bind to receptors on cell surface and be taken up into the cells (internalized by
the cell)
o Important characteristic of the local mediator that determines whether it can act locally or
can be distributed around the body
▪ The hormones that act further away in the body have to be stable enough to get into
the blood, travel through the blood, and get to the target organ not degraded
immediately by enzyme or taken up by cells **IMPT**
AUTOCRINE SIGNALLING (Auto = self)
- Cell releases a signaling molecule that acts back upon receptors expressed on its own surface to
control its activity
- Examples of ligands:
o Cytokine interleukin-1 in monocytes
o Vascular endothelial growth factor (VEGF) in cancer cells
- It has a receptor on its cell surface for that molecule
o A method for the cell to signal to itself that something is happening
o Note: other cells around it can have the receptor
- CELL THAT RELEASES THE LIGAND, HAS A RECEPTOR FOR THAT LIGAND
- Purpose of the ligand-receptor interaction: tell the cell that released the ligand to do a certain job
- Cell may be releasing molecules (e.g. hormone) that is going away from the cells; endocrine or
paracrine
o BUT the cell that released it also has those receptors that way the cell knows that it did
its job!
- OR it can be multiple substances being released; hormone, molecules
o It does not have to be the same molecule!
o Often release substance from granules in the cell there are multiple substances in the
granule
▪ Some may be autocrine, and some endocrine factors
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find more resources at oneclass.com
Document Summary
Signals originate from: environment, other cells, enable us to stay alive. Communicate by sending out signals from hormones, neurotransmitter, chemicals released, etc. Signaling molecules remain bound to surface of signaling cell. Activate target cells that come into contact with signaling cell. Target cell will express a cell surface signal a signaling cell will have a ligand to interact with it. Endocrine cells release hormones into the bloodstream - transported throughout body (signaling over long distances) Hormones act on target cells that express a receptor for the ligand. Hormone signaling is a relatively slow (minutes-hours-days) Long distance signaling release hormone get into blood system and travel around the body. Find target cell based on the receptors that are expressed on the surface of the target cells: target cell can be on the other end of the body. Target cell that will respond to it, will only be those that express that specific receptor; no receptor.
