WBR235

Author	PageAuthor::Gerald Chi
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Pharmacology, MainCategory::Physiology
Sub Category	SubCategory::Cardiology
Prompt	[[Prompt::A 30-year-old postdoctoral scholar in a research laboratory develops a novel agent that preferentially targets smooth muscle cells in the coronary vessels. After injecting the drug to herself, she begins to have repeated attacks of profound substernal discomfort that prompt evaluation in the emergency room. Physical examination is insignificant, vital signs are within normal range. Electrocardiogram shows modest ST-segment depression in lead I, aVL, and V1-3. Which of the following events is most likely to be produced by the drug?]]
Answer A	AnswerA::Activation of protein kinase A
Answer A Explanation	[[AnswerAExp::Incorrect Activation of protein kinase A causes phosphorylation of the myosin light chain kinase, which turns off its activity and results in vasodilation. ]]
Answer B	AnswerB::Activation of protein kinase G
Answer B Explanation	[[AnswerBExp::Incorrect Activation of protein kinase G activates myosin light chain phosphatase and results in vasodilation. ]]
Answer C	AnswerC::Activation of phospholipase C
Answer C Explanation	[[AnswerCExp::Correct PLC is induced upon ligand binding to Gq protein-coupled receptor. which results in cleavage of PIP2 into IP3 and DAG. IP3 mobilizes calcium from sarcoplasmic reticulum and raises cytoplasmic calcium concentration, while DAG activates the protein kinase C and results in vasoconstriction. ]]
Answer D	AnswerD::Inhibition of calcium binding to the troponin C subunit
Answer D Explanation	[[AnswerDExp::Incorrect Calcium binding to the troponin C subunit is involved in the contraction of cardiac muscles rather than smooth muscles. ]]
Answer E	AnswerE::Decreased expression of gene encoding phosphodiesterase 5
Answer E Explanation	[[AnswerEExp::Incorrect Phosphodiesterase 5 converts cyclic GMP to 5'-GMP. Cyclic GMP activates protein kinase G and causes vasodilation. ]]
Right Answer	RightAnswer::C
Explanation	[[Explanation::The novel agent is likely to cause vasospasm of coronary arteries that produces angina symptoms in the patient. Multiple signaling pathways are involved in modulation of contraction and relaxation of vascular smooth muscles. Educational Objective: References: ]]
Approved	Approved::No
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