Nitric Oxide Receptors

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Nitric oxide receptors are intracellular - the receptors are in the nucleus of the target cell.  When a ligand, nitric oxide, binds to the receptor it causes a conformational change.  This initiates a secondary messenger pathway.


1.  Nervous stimulation ie an action potential causes acetylcholine to be release at a synapse.

2.  At a synapse with an endothelial cell, acetylcholine causes an influx of calcium ions into the cell.

3.  Calcium ions activate the enzyme nitric oxide synthase to turn arginine into nitric oxide [1].

4.  Nitric oxide diffuses out of the cell and into the target cell containing the nitric oxide receptor.

5.  Nitric oxide binds to iron in the active site of the enzyme guanylyl cyclase, stimulating the production of cyclic GMP using GTP as an energy source.

6.  cGMP activates secondary messenger pathways which cause the rapid relaxation of smooth muscle cell.

Nitric Oxide

Small, hydrophobic molecule that can diffuse through the cell membrane.  It only acts locally as it has a short half-life of 5-10 seconds.

Nitric oxide is important as it signals blood vessels to dilate by relaxing smooth muscle cells enhancing the blood flow through the vessels.


  1. Alberts et al, (2008) Molecular Biology of the Cell, Garland Science: New York, p888
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