Nitric Oxide

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Nitric oxide (NO) is a gaseous intracellular signalling molecule synthesised from the amino acid arginine, by enzymes called NO synthases. NO is a small, hydrophobic molecule, allowing it to pass easily between cell membranes and spread between cells to exert its effect. One of the main roles of NO in mammalian cells is to act as a smooth muscle relaxant.


Relaxation of smooth muscle in vasculature: Nerves that innervate blood vessels release Acetylcholine, which in turn activates the synthesis of NO from arginine (by action of NO synthases) in the endothelial cells of the blood vessels. NO binds to guanylyl cyclase which stimulates the production of cyclic GMP (cGMP). cGMP causes a cascade which leads to the relaxation of the surrounding smooth muscle in the blood vessel[1].


  1. Alberts et al Molecular Biology of the Cell 5th edition (2008) 887-888

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