WBR0444

Author	[[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Serge Korjian)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Physiology
Sub Category	SubCategory::Renal
Prompt	[[Prompt::A researcher is studying the intracellular signaling pathways of anti-diuretic hormone (ADH) prior to its terminal hormonal effects. He observes that ADH molecules have several different binding sites in renal tissues. Which of the following intracellular signaling pathways is utilized by ADH V2 receptors to increase water reabsorption in the collecting ducts?]]
Answer A	AnswerA::G-coupled receptor pathway that eventually activates protein kinase A
Answer A Explanation	AnswerAExp::G-coupled receptor pathway that eventually activates protein kinase A is the signaling pathway of ADH V2.
Answer B	AnswerB::Receptor or intrinsic tyrosine kinase signaling pathway that eventually utilizes adapter protein
Answer B Explanation	AnswerBExp::This pathway is utilized by insulin and other growth factors, not ADH.
Answer C	AnswerC::G-coupled receptor pathway that eventually activates protein kinase C
Answer C Explanation	AnswerCExp::This pathway is utilized by ADH V1.
Answer D	AnswerD::G-coupled receptor pathway that eventually inhibits the activity of adenylyl cyclase
Answer D Explanation	AnswerDExp::Gi-coupled receptor pathway inactivates adenylyl cyclase. On the contrary, ADH V2 receptor activate adenylyl cyclase by acting on the Gs-coupled receptors.
Answer E	AnswerE::G-coupled receptor pathway that eventually activates leads to formation of inositol triphosphate
Answer E Explanation	AnswerEExp::This pathway is utilized by ADH V1.
Right Answer	RightAnswer::A
Explanation	[[Explanation::There are several signal transduction pathways utilized by receptors to conduct impulses or to execute downstream functions. Receptors are classified based on these downstream effector pathways. The major receptor subtypes are: G protein-coupled receptors, receptor tyrosine kinases, integrin-RTK receptors, toll-like receptors, ligand or voltage-gated ion channels, and nuclear and cytoplasmic receptors. It is important to note that the signaling pathway utilized by ADH V2 receptors (AVPR2) is different from ADH V1 receptors (AVPR1). The ADH V2 receptor is a G-protein coupled receptor that activates the stimulative regulative G-protein (Gs) pathway that activates adenylyl cyclase. The latter catalyzes the conversion of ATP to cyclic AMP (cAMP) that activates protein kinase A. The activity of PKA causes the insertion of aquaporin-2 (AQP2) channels (water channels) allowing water reabsorption down an osmotic gradient at the luminal surface of the collecting duct cells. ADH binds the AVPR2 receptors on the basolateral membrane of the cells lining the collecting ducts. On the other hand, ADH V1 utilizes another signaling pathway; the Gq-coupled receptor pathway that activates phospholipase C and ultimately leads to formation of inositol triphosphate (IP3) and diacyl glycerol (DAG) and activation of protein kinase C. Educational Objective: ADH V2 receptor activates the Gs-coupled receptor pathway that activates adenylyl cyclase. The latter catalyzes the conversion of ATP to cyclic AMP (cAMP) that activates protein kinase A leading to aquaporin-2 insertion on the luminal surface of collecting duct cells. References: ]]
Approved	Approved::No
Keyword	WBRKeyword::signaling, WBRKeyword::pathway, WBRKeyword::G couple, WBRKeyword::receptor, WBRKeyword::protein, WBRKeyword::kinase A, WBRKeyword::Anti, WBRKeyword::diuretic, WBRKeyword::hormone, WBRKeyword::ADH
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Order in Linked Questions	LinkedOrder::