Glucagon's ability to stimulate hepatic glycogenolysis is mediated by the sequence:

• A Glucagon → IP3 → Ca2+ → calmodulin → glycogen phosphorylase directly
• B Glucagon → Gs → adenylyl cyclase → cAMP → PKA → phosphorylates phosphorylase kinase → activates glycogen phosphorylase ✓
• C Glucagon → Gi → inhibits adenylyl cyclase → dephosphorylates glycogen synthase
• D Glucagon → JAK-STAT pathway → transcription of glycogen phosphorylase gene

Explanation

Glucagon binds its GPCR coupled to Gs, activating adenylyl cyclase to produce cAMP; cAMP activates PKA, which phosphorylates and activates phosphorylase kinase, which in turn phosphorylates glycogen phosphorylase b to the active a form, releasing glucose-1-phosphate from glycogen. The IP3/Ca2+ pathway is used by vasopressin V1 and alpha-1 adrenergic receptors. JAK-STAT is used by cytokines and growth hormone.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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