cell to cell communication

mediator

is a chemical, peptide or protein that conveys information from one cell to another

it is considered a mediator if:

1. it is released from cells in sufficient amounts to produce a biological action on target cells within an appropiate time frame

2. application of an authentic sample mediator reproduces the original biological effect

3. interference with the synthesis, release or action ablates or modulates the original response

What were the original names given to acetylcholine by Otto Loewi and Henry Dale?

Vagusstoff.

contact dependent signalling

• requires direct contact between the signalling and the target cell

• usually gap junctions (proteins) or membrane bound signalling molecules

paracrine signalling

• cells release signaling molecules that bind to and activate nearby cells (acts locally)

• mediators are stored in vesicles and are synthesised on demand

autocrine signalling

• a cell releases a signaling molecule that binds to receptors on its own surface, triggering a response within the cell. This allows a cell to self-regulate its activities.

neuronal signalling

• Uses synapses

• Restricts signaling to specific target cells

• Synapses may be short or long distances from neuronal cell bodies

• Chemical mediators of neuronal signaling are neurotransmitters

endocrine signalling

•   A cell signals to cells distributed widely in the body

•   Signaling mediators are secreted into the bloodstream (hormones)

• A hormone can be a protein, steroid or amino acid derived

2 ways chemical mediators are synthesised:

1. synthesis of small molecular mediators are regulated by enzymes (which mediators a cell makes will depend on which enzymes are active)

2. synthesis of peptides is regulated by transcription (which mediators a cell produces is dependent on which genes are active (cells can produce multiple types of mediator and secretory vesicles can store more than 1 type of mediator))

2 groups of chemical mediators

• mediators which are pre-formed, stored in vesicles from which they are released by exocytosis. this allows for rapid communication and can include small molecule mediators and peptides

• mediatoes produced on demand and released by diffusion or constitutive secretion. this takes longer to act