USMLE (United States Medical Licensing Examination) Practice Exam 05
Practice exam for USMLE (United States Medical Licensing Examination).
Question 1
MEDIUMA 62-year-old man with long-standing hypertension is started on a medication that reduces afterload by increasing intracellular cGMP in vascular smooth muscle. Two days later, he reports facial flushing and a throbbing headache. Which of the following best describes the mechanism by which increased cGMP causes vascular smooth muscle relaxation?
cGMP (via protein kinase G) promotes vascular smooth muscle relaxation primarily by activating myosin light-chain phosphatase, which dephosphorylates myosin light chains and reduces actin-myosin interaction. Inhibition of L-type calcium channels is more characteristic of dihydropyridine calcium channel blockers. Opening ATP-sensitive K+ channels is a mechanism of drugs like minoxidil.
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