Simple mechanism of Nitric oxide at the cellular level. Read the description below !

Nitric oxide is a potent vasodilator and is used in conditions involving vasoconstriction.
This video is a simple flowchart to explain the mechanism of how NO causes vasodilation
For a more Elaborate understanding you might read this following description

Cyclic-GMP activates  Protein kinase G
This cause reuptake of Ca2+ and the opening of calcium-activated potassium channels.
Ca++ inside the cells fall.
The myosin light-chain kinase (MLCK) can no longer phosphorylate the myosin molecule, thereby stopping the crossbridge cycle and leading to relaxation of the smooth muscle cell

Remember Ca++ increase can cause NO synthase enzyme activation that increases NO. But N.O. leads to fall in Ca++ that causes relaxation of muscle cells

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