Nitric oxide (NO) synthesized by endothelial NOS causes vascular smooth muscle relaxation by activating:

• A Adenylyl cyclase → cAMP → PKA → myosin light chain dephosphorylation
• B IP3 receptors → Ca2+ release → calmodulin activation
• C Soluble guanylyl cyclase → cGMP → PKG → myosin light chain dephosphorylation ✓
• D Receptor tyrosine kinase → RAS → MAPK → vasodilation gene expression

Explanation

NO diffuses into smooth muscle cells and binds the haem group of soluble guanylyl cyclase, producing cGMP; cGMP activates PKG (protein kinase G), which phosphorylates myosin light chain phosphatase and MLCK inhibitor proteins, leading to smooth muscle relaxation. cAMP relaxes smooth muscle via different kinase pathways (beta-2 adrenergic). Ca2+ and MAPK pathways cause contraction or proliferation.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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