APK 2105C Lecture Notes - Lecture 33: Phenoxybenzamine, Vasoconstriction, Alpha-Adrenergic Agonist

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Chapter 5, Lecture 3
Chemical Messengers
Signal transduction mechanisms
o Binding of messenger molecule to target cell receptor
Location of receptor depends on whether the messenger is lipophilic or
Membrane receptor (water-soluble)
Cytosolic receptor (fat-soluble)
Nuclear receptor (fat-soluble)
o Results in changing the activity of proteins OR stimulation of protein synthesis (or
inhibition) in the target cell
Properties of target cell receptors
o Receptors are very specific
Different affinities for specific chemical messengers within a class
Might be able to bind multiple catecholamines but might want to
bind with one type over the other more
Multiple cells will be exposed but only a very will actually be affected
because of this
o Target cells possess many different receptors
Multiple types of messengers can act on any given cell
o Receptor binding and magnitude of target cell
response to a messenger
Graph looks like enzyme activity
Increases and then levels off
Number of receptors that are bound
increases with more concentration of
messenger (ligand receptor binding)
Leveling off is when every single
receptor is bound to a messenger
Chronically low levels of binding will cause
an up-regulation in the number of receptors created
This will increase the chances of receptor binding
Chronically high levels of chemical messengers will cause a down-
regulation in receptorslower target cell response
Ex: chronic drug users
o Cells are bombarded with too much chemical
o Cells down-regulate receptors
o Not as much of an effect on receptorscreates a tolerance
for that drug
o Tries to increase dose of drug to get more effect
Target cell response is also affected by its affinity for the messenger
Will have more binding if there is more affinity
Higher concentration = higher percentage of receptors bound up
to 100%
Higher affinity = faster rate of binding
o Receptor agonists vs. antagonists
Not all receptor binding results in a response
Agonists = ligands that cause cellular response when receptor binding
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