Antidiuretic hormone increases the water permeability of the collecting duct. Which intracellular sequence correctly describes this action?
- A Binding to V2 receptors activates adenylyl cyclase, and the resulting cAMP promotes insertion of aquaporin-2 channels into the apical membrane ✓
- B Binding to V1 receptors activates phospholipase C, and IP3-mediated calcium influx inserts aquaporin-1 into the basolateral membrane
- C Binding to V2 receptors opens apical sodium channels, creating the osmotic gradient that draws water out of the lumen
- D Binding to V1 receptors activates protein kinase A, phosphorylating aquaporin-2 and increasing its apical expression
Correct answer: A. Binding to V2 receptors activates adenylyl cyclase, and the resulting cAMP promotes insertion of aquaporin-2 channels into the apical membrane
Explanation
ADH binds Gs-coupled V2 receptors on principal cells of the collecting duct, raising cAMP and activating protein kinase A. PKA phosphorylates aquaporin-2 stored in cytoplasmic vesicles, triggering its trafficking to the apical membrane, where it permits luminal water entry down the medullary osmotic gradient. Aquaporin-3 and -4 are constitutively present basolaterally. V1 receptors act via phospholipase C and mediate vasoconstriction, not water permeability, which eliminates options B and D.
Reference: Guyton and Hall Textbook of Medical Physiology, 14th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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