Cardiovascular System MCAT Practice Question
A 58-year-old man with a 15-year history of poorly controlled hypertension presents to clinic with persistent blood pressure of 162/98 mmHg despite lifestyle modifications. Laboratory studies reveal elevated plasma renin activity and serum aldosterone levels. A renal artery duplex ultrasound is normal, ruling out secondary causes. Vascular biopsy of a small resistance artery demonstrates increased expression of angiotensin II type 1 (AT1) receptors on vascular smooth muscle cells compared to normotensive controls. Which of the following best explains the molecular mechanism by which increased AT1 receptor signaling contributes to the sustained elevation in vascular tone in this patient?
Answer choices
- AAT1 receptor activation via Gq proteins stimulates phospholipase C, generating inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG), leading to intracellular calcium mobilization and protein kinase C activationCorrect answer
- BAT1 receptor activation directly opens ATP-sensitive potassium channels, causing hyperpolarization and smooth muscle relaxation
- CAngiotensin II binding to AT1 receptors enhances adenylyl cyclase activity, increasing cAMP production and promoting smooth muscle contraction
- DAT1 receptor signaling phosphorylates and inactivates myosin light chain phosphatase, preventing smooth muscle relaxation
- EAT1 receptor activation functions as a ligand-gated calcium channel, depolarizing the smooth muscle cell membrane independent of G-protein signaling
- FAT1 receptor engagement stimulates soluble guanylate cyclase, increasing cGMP levels and activating vasodilatory pathways
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