Inositol and cAMP Signaling

Inositol and cAMP signaling constitute major second messenger systems. Some GPCRs are coupled to adenylyl cyclase (AC) and ligand-receptor binding activates AC and increases cAMP production. cAMP activates protein kinase A (PKA) which goes on to phosphorylate and activate target proteins.


Other GPCRs are coupled to phospholipase C (PLC) and ligand-receptor binding allows Gα to activate the enzyme, which cleaves PIP2 into DAG and IP3. IP3 acts on sarcoplasmic reticulum IP3 receptors and allow release of Ca2+ into the cytosol. Depending on the cell type this stimulates contraction, secretion or acts as a second messenger by binding to calmodulin and activating PKA.