MadSci Network: Biochemistry

Re: besides drugs what would inhibit a neurotransmitter attaching to receptor

Date: Mon Feb 28 12:11:59 2000
Posted By: Terry Hebert, Faculty, Universite de Montreal, Biochemistry, Montréal Heart Institute
Area of science: Biochemistry
ID: 951440892.Bc

Hello Heather,
	You raise an interesting question. Drugs that interfere directly with 
the binding of a neurotransmitter (NT) to a receptor are called antagonists 
and they can compete for the binding site. However, a lot of other 
modulating factors can also affect the affinity of the receptor for any 
given NT. Certain drugs can bind at sites other the ligand binding site and 
cause allosteric changes in the conformation of the receptor which in turn 
can alter the affinity of the ligand binding site. A good example of this 
occurs at the NMDA-sensitive class of glutamate receptors. Glutamate binds 
at the ligand binding site and causes the NMDA receptor to open an 
intrinsic cation channel which is also part of its structure. Glycine, 
another neurotransmitter with it's own receptor, can also bind the NMDA 
receptor, but not at the binding site and can potentiate the effects of 
glutamate by an allosteric mechanism. For another class of receptors which 
by the NT GABA, drugs such as benzodiazepines have similar effects. Also, 
one must keep in mind that all of these receptors are transmembrane 
proteins which means they have surfaces exposed to the outside and the 
inside of the cell. Those areas exposed to the inside (so-called 
cytoplasmic domains) are sensitive to modulation by protein kinases (which 
can phosphorylate the receptor), phosphatases (which have the opposite 
effects) and a host of other cellular proteins. Modulation of the 
cytoplasmic domains can have dramatic effects on the extracellular binding 
site thus reducing or increasing the affinity for the NT. So you see, it's 
not just the binding site itself that determines the affinity for the 
ligand but rather the global state of the receptor. Hope this helps,


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