Cell to Cell Communication Flashcards
What is a mediator?
Chemical, peptide or protein that conveys information from one cell to another
Released in response to a stimulus and produces a biological response
e.g. contraction of SM, secretion from gland
What is the criteria that establishes a substance as a mediator?
1) Released from cells in sufficient amounts to produce a biological action on target cells within an appropriate time frame
2) Application of an authentic sample of the mediator reproduces the original biological effect
3) Interference with the synthesis, release or action (e.g. receptor selective drugs, enzyme inhibitors) ablates or modulates the original response
What is signal transduction?
Process of converting an extracellular signal to an intracellular signal
Generally how does cell signalling work?
Chemical mediators (extracellular signal molecules e.g. hormones NTs) diffuse in and bind to specific receptors on target cells
This initiates intracellular signals that alter cell behaviour through effector proteins - cell signalling
What are the types of cell signalling?
Contact-dependent
Paracrine
Autocrine
Neuronal
Endocrine
What is contact-dependent signalling?
Has shortest range
e.g. in development - Delta-notch signalling
e.g. in immune response - T cell receptors interact with receptors on APCs
What is paracrine signalling?
Extracellular mediators that act locally
Mediators stored in vesicles in cells - exocytosis (proteins, charged molecules)
Or synthesised on demand (steroid hormones) as can directly cross membrane
e.g. Histamine - vesicles
Nitric oxide
Eicosanoids (prostaglandins)
What is autocrine signalling?
Mediators released by the cell act on the cell itself
What is neuronal signalling?
Uses synapses
Restricts signalling to specific target cells
Synapse can be varying distances from cell body
Fast
Neurotransmitters
e.g. ACh - released as NM junction and heart
Noradrenaline - released at heart
What is endocrine signalling?
Over long distances
Mediators secreted into bloodstream - hormones
Slow
Not specific - cant control where in body it goes but can control which cells have the receptor
What can hormones be?
Proteins e.g. insulin
AA derived e.g. adrenaline
Steroids e.g. estradiol
- All lipid soluble
How are chemical mediators synthesised?
1) Synthesis of small molecular mediators is regulated by specific enzymes
2) Synthesis of peptides is regulated by transcription
- Mediators a cell produces depends on which genes are active
- Cells can produce multiple types of mediators
- Secretory vesicles can store more than one type of mediator e.g. ATP + peptide
What are the two groups of chemical mediators?
1) Pre-formed mediators stored in vesicles - exocytosis
- Molecules reach high conc inside vesicles so rapid communication
e.g. noradrenaline, insulin
2) Produced on demand - diffusion or constitutive secretion
- Longer to act
e.g. nitric oxide, prostaglandins
What is a common regulator of secretion for the mediators?
Ca2+
How is neurotransmitter action terminated?
So that neurotransmission accurately represents action potential frequency
- Enzymes e.g. ACh esterase at cholinergic synapses
- Uptake of NT back into neurones or supporting cells
- Specific transporters in membrane for diff NTs
- Vehicular transporters load NTs into synaptic vesicles
