WBR0936

Author	PageAuthor::William J Gibson
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Biochemistry
Sub Category	SubCategory::Endocrine, SubCategory::Musculoskeletal/Rheumatology
Prompt	[[Prompt::A scientist is studying the mechanism of exercise-induced insulin sensitivity in diabetic patients. A biopsy of the vastus lateralis muscle is obtained from the left leg at rest. 3-6 weeks later, the subjects performed 45-60 minutes of cycling at 70% VO2 max, and immediately thereafter a biopsy was obtained from the right vastus lateralis muscle. The investigator performs immunohistochemistry of the obtained tissues. Which of the following will demonstrate increased localization to the plasma membrane?]]
Answer A	AnswerA::GLUT1
Answer A Explanation	AnswerAExp::GLUT1 is expressed in erythrocytes and the brain. It does not translocate to the cell membrane with exercise.
Answer B	AnswerB::GLUT2
Answer B Explanation	AnswerBExp::GLUT2 is a bidirectional glucose transporter that is expressed in pancreatic islet cells, the liver and the kidney. It does not translocate to the cell membrane with exercise.
Answer C	AnswerC::GLUT3
Answer C Explanation	AnswerCExp::GLUT3 is primarily expressed in neurons and does not translocate to the cell membrane with exercise.
Answer D	AnswerD::GLUT4
Answer D Explanation	AnswerDExp::GLUT4 is an insulin-responsive glucose transporter found in adipose tissue and muscle that translocates to the cell membrane upon exercise.
Answer E	AnswerE::GLUT5
Answer E Explanation	AnswerEExp::GLUT5 is a fructose transporter expressed on the apical border of enterocytes in the small intestine. It does not translocate to the cell membrane with exercise.
Right Answer	RightAnswer::D
Explanation	[[Explanation::Glucose is a charged molecule that requires transporters to enter cells. The glucose transporters found in various cell types in the body are differentially expressed and regulate glucose uptake differently. GLUT4 is the insulin responsive glucose transporter. It is expressed in muscle and adipose tissue, and its cell-surface expression can be increased by exercise. The following table summarizes the glucose transporters. Educational Objective: GLUT4 is an insulin-responsive glucose transporter found in adipose tissue and muscle that translocates to the cell membrane upon exercise. References: First Aid 2013 page 288 First Aid 2012 page 315 Lund S, Holman GD, Schmitz O, Pedersen O. Contraction stimulates translocation of glucose transporter GLUT4 in skeletal muscle through a mechanism distinct from that of insulin. Proc Natl Acad Sci USA. 1995;92(13):5817-21.]]
Approved	Approved::Yes
Keyword	WBRKeyword::Muscle, WBRKeyword::Insulin, WBRKeyword::Glucose, WBRKeyword::Receptor, WBRKeyword::Exercise, WBRKeyword::Transporter
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::