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ADH Aquaporin-2 — FRCA Primary MCQ

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HardPhysiology - RenalADH Aquaporin-2FRCA Primary

Vasopressin binds basolateral V2 receptors in collecting-duct principal cells. Which sequence most directly increases luminal water permeability?

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Correct answer: D — Gs activation, increased cAMP, protein-kinase-A activation and apical AQP2 insertion

The best answer is “Gs activation, increased cAMP, protein-kinase-A activation and apical AQP2 insertion”. V2 receptors couple through Gs to adenylyl cyclase, increasing cAMP and PKA activity. This promotes trafficking of AQP2 to the apical membrane, permitting water entry from tubular fluid; basolateral AQP3/4 provide the exit pathway. Gi lowers cAMP, and GLUT4 is an insulin-responsive glucose transporter rather than a collecting-duct water channel.

Reference: RCoA, Primary FRCA syllabus: https://www.rcoa.ac.uk/sites/default/files/documents/2026-01/Primary-FRCA-Syllabus.pdf; Updates and perspectives on aquaporin-2 and water balance disorders: https://pmc.ncbi.nlm.nih.gov/articles/PMC8657825/